Chapter 11: Landscape Evolution in

Chapter 11: LANDSCAPE EVOLUTION in virginia

G. Richard Whittecar Old Dominion University, Norfolk, VA 23464, [email protected] Wayne L. Newell U. S. Geological Survey, Reston, VA 20192, [email protected] L. Scott Eaton James Madison University, Harrisonburg, VA 22807, [email protected]

INTRODUCTION in bedrock type and structure. River valleys, long-term avenues of transportation for the sediment headed for deposition along Landscapes in Virginia formed in response to both local the coast, commonly contain floodplain, terrace and toe-slope processes and global-scale dynamics. Landforms at any one deposits which reflect the history of processes within that river’s location result from the combined influences of rock type, rock drainage basin. The longest and most extensive records of large- structures, weathering, erosion, and sedimentation. At the same scale surface processes exist in marine and estuarine deposits time, each landform is a piece of a broader mosaic generated of the Coastal Plain and continental shelf. Thus, a synthesis by regional processes and dynamics. Mantle processes drive of landscape evolution in Virginia must integrate sedimentary tectonic plate movements; long-term erosion and deposition records preserved on the continental shelf and Coastal Plain with induce isostatic uplift of orogenic belts and subsidence of the history of streams and eroded landscapes of the Appalachian continental shelves; axial wobble and ocean-current fluctuations provinces. push climatic change; ice-sheet growth and collapse cause the We develop this synthesis in three steps, first by providing level of oceans and of ice-peripheral bulges to rise and fall— a practical geological description of Virginia’s physiographic these regional processes fluctuate at different rates and affect provinces. We also review recent studies in Virginia that shed local conditions at different intensities through time. It is the light on the landscape evolution in the Commonwealth. Before complex interaction of these processes over millions of years concluding with suggestions for future research, the chapter that created Virginia’s landscapes. explains the geological ’s largest rivers. Erosional, transportational, and depositional processes alter Because most of the watersheds for the state’s large streams cross the landscape and provide evidence of the timing of land-forming more than one physiographic province, the collective histories events in Virginia. Hilltops and side-slopes principally carry of these large rivers encapsulate much of our understanding of Figureremnants 1 (half of local page) erosional processes, as controlled by variations the landscape evolution of Virginia (Figure 1).

Figure 1. Map of Virginia’s drainage basins, major streams, and important cities and towns. Basin boundaries - heavy lines.

159 The Geology of Virginia

PHYSIOGRAPHY OF VIRGINIA southern consists of sediments eroded from the upland core of Delmarva to the north and transported Overview southward by waves and longshore drift. The western Coastal Plain boundary approximately parallels the Fall Zone, trending Much of Virginia’s boundaries follow natural features from the mouth of Great Falls on the Potomac River southward (Figure 1). The northern boundary is the southern shore of through Fredericksburg, Richmond, and Emporia. the Potomac River which encompasses both fluvial and tidal We begin our tour of Virginia in the Piedmont, the province environments. The Atlantic Ocean defines the eastern margin with the oldest rocks and most complex geological history, of Virginia. The southern border with North Carolina is a and then progress west across the other provinces born in the generally east-west surveyed line that originally extended from Appalachian orogeny—the Blue Ridge, the Valley of Virginia, a now-closed “Currituck Inlet” on the Atlantic shore (Henry, the Ridge and Valley, and the Allegheny Plateau (Figure 2). The 1770; Byrd, 1841) to the Mississippi and Ohio Rivers. The geologic framework and character of the post-orogenic terrains present western border, defined in 1863 during the Civil War, in Virginia—the­­ Lowlands embedded within the largely follows mountainous divides running northeast from Piedmont, and the Coastal Plain blanket farther east—reflect Cumberland Gap, Tennessee to Harpers Ferry, West Virginia at the superposition of rifting, uplift, and subsequent erosion and the confluence of the Shenandoah and Potomac Rivers. sedimentation along the Atlantic margin upon the results of Within Virginia, the physiography largely reflects the that orogeny. The distribution and characteristics of regolith susceptibility of different rock types and patterns to weathering in all these regions reflect the history of geomorphic processes and erosion. Because a physiographic region contains hills operating on the bedrock substrate through geologic time. This and valleys with relatively similar morphology, each region in history thus controls pathways for groundwater flow and the Virginia includes a distinctive suite of relief, rocks, and geologic usefulness and economic value of near-surface materials. structures. Arrayed from northeast-to-southwest across the central and western portions of the Commonwealth, these belts The Piedmont of mountains and valleys follow the trends of the Appalachian orogen with its major rock assemblages and Rising to the west of the Fall Zone, the Virginia Piedmont contractional tectonic structures. Extensional Mesozoic grabens presents rolling convex hills and large entrenched streams that superimposed onto these orogenic belts often contain low-relief grade to sea level at or near the Fall Line. The terrain is generally landforms underlain by relatively mildly deformed sediments underlain by multi-grade metamorphic rocks later pierced by and intrusions. large granitic and other intrusions (Rader and Evans, 1993). To the east, overprinted on this general trend of linear ridges The metamorphic fabric commonly includes steeply-dipping and valleys is the seaward-dipping, gently-inclined wedge of foliation and joints. Harder rock units, including quartzite and Coastal Plain sediments. Generally undeformed, these deposits siliclastic fault zones, frequently form ridges. Valleys generally accumulated from the erosion of the Appalachians since the form along zones of closely-spaced fractures that provide Figure 2 (full page) early . Most Coastal Plain deposits on the western important, secondary porosity that facilitates penetration of shore of the are derived from Virginia’s groundwater and deep weathering. Overall relief, a function of upland interior. However, on the eastern shore of the Bay, the both the degree of stream incision and the number of obdurate-

Figure 2. Map of physiographic features and provinces in Virginia. The shaded area represents the Fall Zone, a transitional boundary across a highly dissected belt of Coastal Plain remnants. ML = Mesozoic Lowlands. Locations of scarp segments after Ator et al. (2005); province and sub-province boundaries after Bailey (1999).

160 Chapter 11: Landscape Evolution in Virginia rock hills, generally increases westward across the Piedmont usually occurs as an isovolumetric residuum that preserves the (Figure 3). original rock fabric and thus maintains a structured permeability The chemically meta-stable mineralogy of most rocks in formed from the void spaces left by the dissolved, labile the Piedmont and long periods of humid-temperate climate in minerals. Commonly, the thin zone of transition from saprolite Virginia resulted in a thick regolith of saprolite and saprolitized to weathered rock to fresh rock is the frontier of chemical surficial deposits under the low-gradient, upland surfaces of the weathering where both the permeability of joint zones and the Piedmont. Chemical weathering processes alter and remove porosity of rock increase through time (Pavich et al., 1989). large volumes of feldspar, mica, hornblende, and other soluble As the Piedmont drainage systems evolve, relatively fresh minerals leaving more resistant minerals, such as , zircon, bedrock exposures usually occur only in the stream bottoms magnetite, ilmenite, and clays. Barring drastic changes in base where flooding has scoured through the regolith, usually in the level, equilibrium thicknesses of saprolite often reach 10 m (33 channels of higher-order streams (Costa and Cleaves, 1984). ft) thick; locally, regolith exceeds 25 m (80 ft) (Hack, 1982; Elsewhere, hard rocks rarely crop out. On eroded slopes and Cleaves, 2000). other surfaces formed over particularly dense lithologies (e.g., Ultimate weathering products can occur in the regolith diabase, greenstone), spheroidally-weathered core stones under broad landscape uplands. There, in the upper portion of studded within saprolite can breach the surface. Cobble- and the regolith, volumetric changes due to leaching can remove boulder-size rubble of angular quartz can occur concentrated all semblance of metamorphic rock fabric, leaving authigenic around outcrops of relatively insoluble veins. Thin zones of and degraded clay minerals and oxides of iron and aluminum quartz and quartzite pebble-cobble lag often cap many of the low- toFigure dominate. 3 (half Deeper page) in the profile beneath uplands, and gradient upland surfaces; the lag deposits are insoluble remnants immediately below the colluvium along many hillsides, saprolite of the down-wasting of massive thicknesses of crystalline rocks.

Figure 3. Shaded DEM image illustrating the Blue Ridge Upland and Blue Ridge Escarpment in southwestern Virginia. View is to the NNW from south-central Virginia. The escarpment is the continuous band of high relief that separates the Piedmont from the southern Blue Ridge southwest of Roanoke. The New River basin drains northwestward across the Appalachian fold belt and flows through a gorge incised into the Appalachian Plateau. The James River flows east through a gorge (JR Gorge) incised through the northern . The Roanoke River and its tributaries (visible in the foreground) also flow eastward. Headwater streams in the Roanoke River network erode steep valleys along the Blue Ridge Escarpment, and occasionally pirate streams originally flowing on the Blue Ridge Upland. Image courtesy of P.S. Prince.

161 The Geology of Virginia

Where abundant on hillsides, such resistant sediments form in this area closely resembles the physiography of the Piedmont stone lines and become concentrated in stream gravels and older province; across this “inner Piedmont” or “foothill zone” the stream terraces (e.g., Whittecar, 1985) and may be interlayered regional topography of the Blue Ridge terrain steepens slightly with colluvium derived from loess caps (Feldman et al., 2000). and more resistant bedrock knobs rise above the rolling upland The properties and distribution of these weathered materials (Hack, 1982). In that area the Piedmont-Blue Ridge geological within the Piedmont regolith influence several aspects of the boundary is a Paleozoic thrust fault that separates high-grade geomorphic system. Weathering generates materials easier metamorphic rocks from older, lower grade Blue Ridge cover to erode and transport. Silt-dominated regolith, such as many rocks and Grenville core rocks to the west (Rader and Evans, saprolite bodies, can develop soil pipes that rapidly transmit 1993). In the Piedmont the aligned valleys of water and sediment across hilly landscapes through shallow the Mountain Run Fault Zone lie along that boundary. Farther subsurface interflow (e.g., Schoeneberger and Amoozegar, 1990; south the geological boundary is also a terrain suture (Rader and Vepraskas et al., 1991). Over time such megapores may promote Evans, 1993) but with no notable topographic break. development of rills and gullies (e.g., Jones, 1971; Dunne, 1980, South of the Roanoke River basin lie the Blue Ridge 1990; Bryan and Jones, 1997). Weathering of different rock types Upland and the Blue Ridge Escarpment. The distinctive feature can produce different thicknesses of saprolite and contrasting of the southern Blue Ridge (Figure 2), the upland is a broad, suites of soil minerals (e.g., Cleaves, 2000). Most often, felsic low-relief plateau studded with a few high-relief mountain igneous and metamorphic rocks contain fewer labile minerals, ranges (e.g., Mt. Rogers and surrounding peaks). Dubbed the so they generate thicker regolith characterized by kaolinite. “Floyd surface” by Erickson and Harbor (1998), this upland Weathering processes produce permeabilities near the base of ends abruptly on the east where bound by the escarpment; an the saprolite that are markedly larger than the permeability of the erosional break that averages 300-500 m (980-1640 ft) relief and weathered and unweathered bedrock below (Buol et al., 2000); stretches from Virginia southward into Georgia (Harbor et al., thus the zone of saturation just above the saprolite-rock interface 2000; Pazzaglia and Gardner, 2000; Spotila et al., 2004; Prince tends to be the near-surface aquifer with the most pronounced and Henika, 2010a, b)(Figure 3). By contrast, in central and groundwater flows. Landscapes underlain by large amounts northern Virginia, only a few low-relief uplands surrounded by of mafic minerals tend to develop thinner saprolite that forms precipitous slopes cap the Blue Ridge crest at isolated locations soils with higher volumes of 2:1 expandable clays (Pavich et (e.g., Wintergreen resort area, Nelson County; Big Meadows al., 1989; Sherwood et al., 2010). On the Piedmont landscape, area, Shenandoah National Park). this fresh rock/weathered rock zone plays a major role in the The position of the continental divide changes dramatically headward erosion of springs and the eventual entrenchment of between the southern and northern portions of the Blue Ridge evolving drainage systems along fracture-controlled weathering province. In the southern Blue Ridge the continental divide zones (e.g., Newell, 1970). The result of these processes is a follows the crest of the Blue Ridge escarpment and separates fabric of topographic elements that reflect both the geometry of the New River watershed from the Roanoke and James drainage fracture systems and the trends of resistant rock types. basins (Figure 1). The New River watershed drains the southern Blue Ridge upland towards the Mississippi River and the Gulf The Blue Ridge of Mexico. Between Roanoke and Blacksburg, the continental divide shifts northward into West Virginia, from the Blue Ridge Much of the highest topographic relief in Virginia occurs escarpment to the Allegheny Front (the eastern edge of “flat in the Blue Ridge Mountains (Figure 2), a belt of mountainous lying” rocks of the Allegheny Plateau). This shift reflects that terrain underlain by meta-igneous and meta-sedimentary rocks. throughout the northern Blue Ridge in Virginia, the Roanoke, Local relief on the Blue Ridge terrain increases to several hundred James, and Potomac Rivers breach the crest of the Blue Ridge; meters along the crest of the Blue Ridge. Although zones of high sediment and water gathered from the Valley of Virginia and relief and the presence of saprolite characterize the Blue Ridge, ridges farther west are transported eastward along those routes neither is uniformly distributed; elevated regions with relatively to the Atlantic. subdued relief exist and broad regions with shallow and exposed Other than along the eastern escarpment of the southern Blue bedrock “balds” are common. Differences in mineralogy, rock Ridge in Virginia, much of the relief in this province stems from solubility, fracture orientations, and local erosional history the lithology and structure of the bedrock. Rocks of the Blue of the high-relief landscapes explain many, but not all, of Ridge are older than the Piedmont Paleozoic meta-sediments, the high elevation, steep topography, and hillslope features but are commonly of lower metamorphic grade; some patches present across the Blue Ridge terrain. Other important factors of higher-grade Grenville-age core rocks lie exposed due to to evaluate include the influence of cold-climate processes at removal of Neoproterozoic cover rocks by erosion (Rader and higher altitudes during the and the potential impact Evans, 1993). High-angle tectonic joint sets influence some of tectonic processes. valley patterns and, where combined with spheroidal exfoliation In this paper we use the geologic boundaries of the Blue joints, commonly define the shapes of outcrops of the meta- Ridge and Piedmont provinces, knowing that these do not igneous rocks. In general, though, across the Blue Ridge terrane coincide with topographically-based boundaries (e.g., Hack, the regional structural fabric is commonly more broadly and 1982). These differences become confusing in northern Virginia openly folded than in the Piedmont, often with low-angle where “the Blue Ridge” is a relatively narrow range with high cleavage and schistosity. relief situated at the western edge of the Blue Ridge geologic Along the topographic crest of the Blue Ridge, broad open province (Figure 2). Most of the northern Blue Ridge province meadows, bedrock tors with sparse slope deposits, and local

162 Chapter 11: Landscape Evolution in Virginia concentrations of large-boulder fields hold evidence of a colder, Valley and Ridge on the west. A wide belt of low hills, terraces, wetter climate with intense, higher-frequency slope processes and flood plains (Figure 2), the Valley of Virginia is largely during the Pleistocene (Whittecar and Ryter, 1992; Eaton et underlain by the and carbonate rocks al., 2003a; Litwin et al., 2004). One effect of the increased (Rader and Evans, 1993) which outcrop from northern Alabama topographic relief and the frequency of more rigorous climates to eastern New York State. Sinkholes and depressional swales at higher altitudes is that regolith with different textures forms occur commonly on many carbonate-rich units (e.g., Hubbard, on the Blue Ridge slopes underlain by distinctively different 1983, 1988). Because most of these beds lie within the limbs of rock types. Coarse colluvium collects downslope of high knobs, plunging folds, the greatest concentrations of prominent karst balds, and tors of various crystalline rocks and quartzite beds; in features develop along linear outcrop belts (e.g., Hyland, 2005). contrast, finer-grained saprolite and transported regolith develop This regional lowland contains geologic structures similar to the on more weatherable granites and meta-sediments other than folded and faulted Ridge and Valley to the west, and so this area quartzite. In first- and second-order stream hollows, catastrophic is usually mapped as a part of that province (e.g., Bailey, 1999). rain storms eventually strip away saprolite plus colluvium Unlike the Ridge and Valley, however, few resistant sandstone transported from ridge slopes (e.g., Eaton et al., 2003b). units surface in the Valley of Virginia so karstic processes East of the Blue Ridge divide, steep ravines fall away to dominate the low-relief landscape. For our discussion we hollows with narrow flood plains. Balds and landslide scars on separate these two geomorphically-distinct regions to emphasize the confining mountain slopes are the source areas of numerous the importance of subsurface drainage through the relatively catastrophic debris flows and flood deposits, usually triggered soluble carbonate rocks and fractured shale beds in the Valley by extreme rainfall during stagnating orographic storms of Virginia. (Clark, 1987; Wieczorek et al., 2000). Such storms, commonly Non-karstic landforms also occur commonly in the Valley associated with intense thunder storms and hurricanes, deluge of Virginia. Prominent hills form many places where chert- intense rainfall onto steep mountain slopes. Extreme over- rich units and sandstone lenses within the carbonates develop saturation of steep slope deposits can overcome the threshold protective residual soil mantles. At least one local promontory, for stability and cause numerous, nearly synchronous debris Mole Hill west of Harrisonburg, marks the neck of an flows to cascade down slopes and valleys. At the confluence of volcano (e.g., Wampler and Dooley, 1975; Gaithright and several tributaries carrying these flows, cumulative volumes of Frischmann, 1986; Tso and Surber, 2006). Local mountains coarse sediment form an alluvial fan in confined valley spaces, with high relief, including the Massanutten Mountain range, deposited at grade for a kilometer or more down the valley. The arise from the lowland where in-folded and faulted masses of headwaters’ flood plains are largely constructed during these resistant sandstone/quartzite cap a thick sequence of extreme discharge events and modified later by the flow of water Ordovician shales which overlie the more soluble carbonates. and sediment. Downstream from these zones of constructive Due to the high solubility-induced relief along both the topography, the streams commonly have enough power to erode east and west borders of the Valley of Virginia, large volumes and deposit alluvium and develop classic equilibrium profiles of coarse siliciclastic sediment eroded from the Blue Ridge as they transport water and sediment eastward across the and the Ridge and Valley lie draped over buried carbonate Piedmont. Ancient terraces and inactive fan surfaces, some that landscapes and line the margins of stream valleys (King, 1950; may predate the Quaternary, indicate that changes in base level Hack, 1965). Some of these alluvial fans and terraces contain and other perturbations altered the equilibrium of this dynamic relatively old sediment (e.g., Whittecar and Duffy, 2000). system multiple times throughout geologic time (e.g., Dunford- These ancient deposits function as shallow aquifers in the karst Jackson, 1978; Youngblood, 1998; Eaton et al., 2003a; Hancock system and contribute to the dissolution of the while and Harbor, 2003). protecting the resulting insoluble residue (terra rosa) from Western slopes of the northern Blue Ridge Mountains are erosion. The resulting topography and surficial deposits include commonly steep with outcrops and talus formed of resistant inset sequences of alluvial fans, flights of river terraces, and quartzite, greenstone and meta-sediments. Talus deposits intervening hills of residual regolith and outcrops. Most of these cascade precipitously to broad alluvial fans that engulf the landforms are punctuated by systems of sinkholes that frequently margins of the carbonate /Valley of Virginia follow the linear trends of fractures and particularly soluble beds landscape. The extensive alluvial fans that coalesce into of various Cambro-Ordovician carbonate formations. westward-graded bahadas and pediments consist of resistant Approximately the northern third of this karst terrain, cobbles and boulders that bury karst landforms, and protect the known as the Shenandoah Valley, feeds the Shenandoah River, underlying saprolite and weathered surficial deposits formed on a north-flowing tributary of the Potomac River that dissects Paleozoic carbonate bedrock. The effect is a multi-storied array the Blue Ridge on its eastward course to the Chesapeake Bay of fans and pediments graded to various old base levels of the (Figure 2) . The central third of the Valley of Virginia is drained Shenandoah, upper James, Roanoke, New and other rivers and by the headwaters of the James River and the Roanoke River their tributaries (King, 1950; Hack, 1965; Whittecar and Duffy, that also breach the Blue Ridge topography and flow east to 2000). the Chesapeake Bay and Albemarle Sound, respectively. The southwestern extent of the Paleozoic carbonate belt is drained The Valley of Virginia by the New River, Clinch, and Holston Rivers whose flows eventually reach the Gulf of Mexico. The New River originates The Valley of Virginia landscape consists of a broad lowland in the Blue Ridge of North Carolina, and as it flows northwest bounded by the Blue Ridge on the east, and the first ridge of the toward the Ohio River, it transects the trend of the Appalachian

163 The Geology of Virginia fold-and-thrust belt. Southwest of the New River watershed, where local relief commonly exceeds several hundred meters. drainage from the Paleozoic carbonate belt flows southwest Limestone with karst terrain or shale and siltstone with gently along the structural trend of the ridges and valleys. These rolling terrain underlie the valleys. watersheds of the Clinch and Holston Rivers are tributaries of The axiom is less accurate in some areas, however, because the Tennessee River (Figure 2). of thicknesses of strata and sizes of structures. Paleozoic Several of these rivers have entrenched their valleys rock sequences in these regions commonly contain different deeply into the rock substrate. Where the entrenched rivers lithologies that rarely exceed a few hundred meters and often transect structural belts and intensely-fractured rocks, joint are much thinner. The largest fold wavelengths in this terrain control by steep, northwest-southeast fractures has produced commonly reach several kilometers, but may produce high-dip distinctive elongated patterns of meandering bedrock channels and overturned bedding on fold limbs. In this geologic setting with amplitudes that are commonly two-to-four times the with high dips and numerous rock types, landslide-inducing wavelength. The North and South Forks of the Shenandoah shale and cave-forming limestone can lie interbedded along contain outstanding examples of these oriented, entrenched, the flanks of the many sandstone-capped mountain ridges (e.g., meandering channels (Hack and Young, 1959). Schultz and Southworth, 1989; Peterson and Whittecar, 2007). High local relief caused by stream entrenchment imparts a The largest valleys form on gently-inclined formations along steep gradient to the ground-water table within adjacent landforms the axes of anticlines and synclines. Limestone beds in these that has facilitated development of clusters of sinkholes and the positions develop doline plains, disappearing streams, and other networks of cave systems that rapidly feed baseflow to streams. distinctive surficial karst landforms (Hubbard, 1988). Broad As the stream lowers its base level through time, successively expanses of weathered siltstone and shale lying at shallow dips lower cave levels drain, thus allowing dripstone to form. commonly contain ridge-and-ravine topography with moderate The speleothems and sediments from through-flowing rivers relief; only thin surficial deposits drape these steeply-gullied preserved in these caves commonly prove useful in establishing hillsides. The fabric of Appalachian shale landscapes commonly the timing and rates of river incision (e.g., Granger et al., 1997; reveals accelerated erosion along structural weaknesses. Where Hancock and Harbor, 2003; Ward et al., 2005). However, the shale terrains are interposed between the sandstone-quartzite rapid transmission of water through fractures and caves also ridges and the limestone valleys, sloping pediment-like landforms allows contaminated highway, urban, and agricultural runoff have commonly developed. Thin colluvial deposits of resistant to enter drinking water supplies with little alteration. This sandstone boulders are graded across the shale bedrock to valley situation, coupled with the high rates of surface runoff that drain bottoms developed on the carbonate rocks. Classic gully gravure from clay-rich soils compacted by farming of limestone-based sequences of episodic incision by small streams and reworking soils, make the region susceptible to numerous surface- and of the resistant slope deposits occur on many valley sides; these ground-water-quality issues. sequences reveal the influence of progressive lowering of base level in the main valleys (e.g., Mills, 1981). The Ridge and Valley These colluvial slope veneers are extensive, common, and usually thin, although aggradation may form coarse deposits Within the Ridge and Valley, the middle and upper Paleozoic tens of meters thick. Commonly both siltstone/shale beds and stratigraphic sequences of sandstone, shale, and limestone limestone beds that are covered with this permeable colluvium crop out in a northeast-to-southwest belt of linear mountains and alluvium are deeply weathered. Local ores of iron and and valleys (Rader and Evans, 1993). Individual ridges manganese discovered in slope-transported regolith and in the commonly extend many tens of kilometers without interruption. highly-altered saprolite below were mined early in the history Differential erosion of the siliciclastic and carbonate rock types of occupation of the valley (e.g., King, 1950). Deep leaching of has produced distinctive, high-relief topography that reveals the the regolith on the sandstone and quartzite beds along the upper classic Appalachian fabric of anticlines and synclines, plunging slopes of ridge tops also concentrated insoluble oxides of iron folds, and discontinuous fault slices. Landforms and deposits and manganese in both the Ridge and Valley and the Valley of developed across the eroded surfaces of these rocks can preserve Virginia (King, 1950; Hack, 1965). records of significant geomorphic events. Travertine and tufa springs and falls form in limestone-rich At a broad scale, the geologic axiom “hard rocks form hills, areas of western Virginia; the most notable and possibly largest is soft rocks form valleys” fits this terrain well. The spatial pattern Falling Spring near Covington. Surface waters in karst areas often of the ridges and valleys resulted from the underlying geologic become saturated in calcium. Where turbulence in the stream structures of this fold-and-thrust belt. Many resistant dip slopes permits out-gassing of dissolved carbon dioxide, precipitation define shapes of plunging folds and closed anticlines (domes) of carbonate coating covers the stream bed (Hoffer-French and and synclines (basins). Slopes that cut through stratigraphic Herman, 1989; Herman and Hubbard, 1990). Ground-water, in sequences—the stoss or anti-dip slopes—are commonly much contact with limestone for even longer periods, is also affected steeper than dip slopes, and on many ridges form cliffs with by circulation along geologic structures. Significant ground- coarse talus deposits at their bases. The relief of the ridges and water flow penetrates deeply through both the carbonate rocks, valleys results from the contrasts between the high solubility of and fault and fracture systems in all the rocks. Water forced limestone formations, the low resistance of shale and siltstone by topography and structures to emerge from large depths and strata to physical weathering and erosion, and both the insolubility to re-cross the geothermal gradient relatively rapidly emerges and resistance to physical degradation of sandstone and quartzite as warm springs with anomalously high volumes of dissolved units. The most massive and resistant strata support steep ridges calcium or silica (Nolde and Giannini, 1997). Tufa and travertine

164 Chapter 11: Landscape Evolution in Virginia deposits formed at such springs and at falls potentially contain been more intense and effective at high altitudes, imparting long records of cycles of climate change during the Pleistocene. a periglacial signature on landforms and surficial deposits These records also may be particularly valuable in deciphering in this region (Clark and Ciolkosz, 1988) but removing most the history of landscape evolution where they are interbedded ancient regolith. Thus it is difficult to extend our understanding with colluvium or other hillslope deposits. of landscape evolution back into the early Neogene for this physiographic province. The Allegheny Plateau The Mesozoic Lowlands To the west of the Appalachian fold-and-thrust belt the vast Allegheny/Cumberland Plateau stretches from Pennsylvania Mesozoic basins, in the form of grabens and half-grabens to Alabama and westward across West Virginia, and eastern containing tilted sedimentary rocks and mafic intrusions, lie Kentucky. The mountainous landscape cuts deeply into the within irregular polygons that interrupt landscape patterns generally flat-lying rocks, many of which formed in late Paleozoic formed on the crystalline terranes of the Piedmont and Blue deltas and related terrestrial environments. This geomorphic Ridge (Figure 2) (Rader and Evans, 1993). These fault-bounded system dominated by steep slopes and erosive streams preserves basins opened during the early stages of continental rifting as the few records of geomorphic processes, but contains Atlantic Ocean formed. Some basins, such as the large Culpeper numerous and widespread hazards for human activity. basin in northern Virginia, have broad zones with lower relief The -age deltas accumulated tens of than surrounding landscapes; the smaller basins scattered across thousands of meters of thick clastic sediments stripped from the central and southern Virginia are less distinct topographically. Appalachian-Blue Ridge terrains, and from the Canadian Shield Many of the basins are transected by through-flowing rivers during the continental collision that produced the Alleghenian crossing the Piedmont. deformation. Interspersed with the fluvial/deltaic deposits of The and rock sequences in the basins sandstone, siltstone, shale, and thick coal beds are thin marine consist of continental clastic red beds with some lacustrine beds, carbonate formations (Rader and Evans, 1993). Because and both diabase intrusions and basaltic lava flows (Rader and regional folds in these deposits are very broad and gentle, Evans, 1993). Although the continental sediments commonly high-angle fractures and faults are the principal structures that dip west toward listric fault margins, the broadest land surfaces influence the dendritic-rectangular stream patterns in the region. are nearly-level plains that truncate the easily-eroded shale beds. The small portion of this region that extends into Virginia drains The gentle slopes formed on the reddish shales and siltstones to the Gulf of Mexico, mostly via tributaries of the Ohio River generate relatively high volumes of surface runoff that produce (Figure 2). erosion rates which are locally extreme, especially in heavily- In Virginia, the geomorphic system in the plateau region tilled landscapes. The intrusive and extrusive rocks, rich in consists primarily of actively eroding steep slopes and narrow soluble minerals, commonly weather to clay-rich saprolite which valley bottoms. The high-energy system transports slope and encases rounded core stones of fresh diabase or . Where fluvial sediment rapidly during both seasonal rainfall events and armored with a residual carpet of core stones, the landscapes floods, resulting in narrow floodplains and few terraces. formed on the intrusive rocks are generally less susceptible to Although of relatively limited area in the state, the erosion. Thus, regions with more resistant igneous rock masses Appalachian Plateau is a region of vast economic importance appear as low boulder-strewn hills rising from the low-relief to Virginia, but which has significant geomorphic hazards. plains on the red beds. Thick regolith on the Mesozoic shale Industries that extract coal, and to a lesser extent oil and gas, beds occurs where covered by permeable or resistant surficial operate across this region. In areas with easily-eroded rocks deposits, such as gravel terraces, slope deposits, and possibly and soils, steep slopes, and locally high relief, development loess. activities such as land clearance, mining, site preparation, and house construction require special attention so as not to generate The Atlantic Coastal Plain increased sediment loads, both chemical and clastic, to streams. In addition, the twin hazards of flooding and slope failure The eastern third of Virginia is part of the Atlantic Coastal can impact much of the municipal, residential, and industrial Plain, a vast wedge of marine, estuarine, and fluvial sediment that infrastructure in the area. extends from Long Island to Florida. It contains an extensive Ancient remnant surficial deposits are either minimal or record, not only of the rise and fall of sea level, but also the uplift lacking in the Virginia portion of the Appalachian Plateau. Unlike and erosion of the Appalachian physiographic provinces and the the nearby Valley of Virginia and the Ridge and Valley, which history of the river systems that drain the eastern headwaters of both contain extensive regolith with long records of history of the continent. It also preserves the direct and indirect effects landscape evolution, the Allegheny Plateau surficial sediments of climate changes that altered the magnitude and frequency of appear to have much shorter residence times. Presumably the wind, rainfall, and frost action across the low-relief landscape. lack of accommodation space needed to hold valley-bottom Physiographic details of the Atlantic Coastal Plain are sediments combined with the steep, high-energy environment characteristically simplified as an Inner, Middle, and Outer permit little regolith accumulation. This dearth of deposits Coastal Plain, each zone being separated by a prominent coast- suggests that the region has been more or less continuously wise scarp cut by vigorous marine erosion (Figure 2). Three eroded without significant hiatus for much of the late Cenozoic. scarps with regional extents have clear expression in the Coastal During the Pleistocene, cold-climate processes would have Plain of Virginia (Mixon et al., 1989). The Thornburg Scarp

165 The Geology of Virginia marks a sea level high-stand at or near the inner edge deep regolith so that at the rare, ephemeral outcrops with pre- of the Coastal Plain; a few remnants of more ancient Coastal Pliocene regolith, only a few meters remain. Hack (1982) used Plain deposits lie west of this scarp in the broad Coastal differences in watershed patterns to argue that a sedimentary cap Plain/Piedmont margin. The Surry Scarp, cut during the late extended across the eastern Piedmont. Paleontological evidence Pliocene and/or early Pleistocene separates the Inner from the led Weems and Edwards (2007) to suggest the remnants that cap Middle Coastal Plain. The Suffolk Scarp, carved during the hills as much as 30 km (19 mi) west of the Fall Zone record late Pleistocene, separates the Outer from the Middle Coastal transgressions (Figure 4). Along and immediately Plain. The topographic separations between depositional units landward of the Thornburg scarp in Dinwiddie County, beach on either side of these ocean-facing erosional scarps can exceed sediments contain enormous deposits of heavy minerals that 25 m (82 ft) (Thornburg Scarp) but more often are 3 m (10 ft) or were reworked repeatedly during the Miocene and Pliocene less (Surry and Suffolk scarps)(Johnson et al., 1987). Between (Berquist, 1987; Berquist and Bailey, 1999). Some of the these scarps, landscapes differ according to their elevation and high-level surfaces in this zone display beheaded meandering resulting degree of stream incision that removed the original valleys disconnected from modern streams (Whittecar et al., coastal surfaces and landforms, and the degree of weathering 1994); other surfaces overlay deposits containing reworked and consolidation/cementation of the underlying strata. ferricrete boulders and plinthite nodules, which indicate cycles The regional, coast-wise trend of the stair-stepped pattern of of weathering, erosion, and redeposition that originated in the scarps and terraces and the underlying deposits, each formed higher landscapes long removed. South of Virginia, where the by the marine shoreline of a high-stand event, are interrupted Coastal Plain/Piedmont transition zone west of the Pliocene in Virginia by tributaries to Chesapeake Bay—the Potomac, shoreline broadens greatly, deep weathering created both in situ Rappahannock, York, and James rivers. These southeast- and reworked regolith many tens of meters thick; this regolith flowing rivers are part of the Susquehanna River was uplifted hundreds of meters, and eroded and reworked many system which was deeply incised into the high-stand deposits times (Newell et al., 1980). during the sea level low-stands that accompanied the repeated cold climate events. Aggradation induced by the next marine Inner Coastal Plain geomorphology inundation formed fluvial and estuarine terrace assemblages that lie within each entrenched valley. Where the top of the incised The Inner Coastal Plain preserves a long record of deposition valley was not totally buried by subsequent sedimentation, a and erosion by shorelines and rivers influenced by climate change river-facing scarp separates Pleistocene units of different age. and by isostatic uplift. In northern Virginia, the Thornburg Each valley-filling aggradational sequence is graded to a delta scarp is an early Pliocene shoreline cut into and below the older and outboard marine deposits in the mode of allostratigraphic Coastal Plain/Piedmont landscape (Figure 2). Identified as the formations (e.g., Newell, 1984; Newell and Rader, 1982; Mixon Chippenham Scarp in southern Virginia (Johnson et al., 1987), et al., 1989, 2000). These formations are now recognized as high- this scarp more or less corresponds to the Fuquay-Varina scarp stand systems tracts and falling-sea-level systems tracts. The in northern North Carolina and the Orangeburg Scarp identified repeated incision and partial refilling of these river valleys and southward from there to northern Florida. Seaward of this scarp their tributaries, when combined with analyses of the coastwise in Virginia, gravelly-to-sandy-to-silty facies of the Yorktown scarps and terraces, provides a rich history of the development Formation and Bacons Castle Formation extend to the Surry of the Coastal Plain landscape. Scarp. However, few if any original depositional landforms or large dune fields remain on these flat upland surfaces. Coastal Plain/Piedmont margin Subsurface formations also influence surficial features in the Inner Coastal Plain. Beneath the Pliocene coastal and Traditionally viewed as a narrow zone defined by a few shallow shelf deposits lie older Tertiary and Cretaceous units high terrace fragments, the Coastal Plain/Piedmont transition containing silty clay and fine sand. The burial, exhumation, and consists of a broad overlap zone with many erosional remnants tectonic history of these sediment packages since the Cretaceous of ancient landscapes. West of the Thornburg Scarp, Miocene and Paleogene produced over-consolidated or semi-indurated Coastal Plain sediments occur as relatively thin units capping deposits that are fractured with systematic tectonic joint patterns saprolite. Often they sit on isolated hilltops standing higher than (e.g., Pavich and Obermeier, 1985; Jacobson and Newell, 1982). the surrounding saprolite knolls (Pavich and Obermeier, 1985), Somewhat impermeable and resistant to erosion, these deposits or as subtle plateaus covered with residual lag-gravel deposits, support steep topography and eroded bluffs along the major long ago eroded and reworked by multiple surficial processes. rivers. The discharge of springs at the permeable-impermeable Deeply-weathered fluvial gravel deposits occur lower than these boundary below the surficial aquifer drives the headward plateaus, inset on benches next to the major rivers entrenched erosion of the gully formation throughout the outcrop belt of through the saprolite of the Piedmont rocks. Along the Fall Zone these deposits. Selective headward erosion and fluvial erosion of the Potomac, Rappahannock, and James rivers, upper delta- along river bluffs has created an oriented landscape of ridges plain deposits are co-extensive with the early-middle Miocene and stream valleys across the Inner Coastal Plain. gravels of the Calvert and Choptank Formations. All of these deposits continue to rise upwards on the flank Fragmentary clues suggest that much remains to be of the ancient Appalachians as the mountain belt isostatically discovered about the geologic history of the Coastal Plain/ adjusts to long-term regional erosion (e.g., Pazzaglia and Piedmont transitional zone. In places, significant erosion Gardner, 1994). Thus, the landscapes underlain by these deposits during the Paleogene stripped away much of the formerly are more deeply eroded and stand higher in relief and elevation

166

Chapter 11: Landscape Evolution in Virginia Figure 4 ( full page )

Figure 4. Diagram showing the stages in the development of the modern eastern Piedmont landform during the middle Miocene and Pliocene. A. Late Serravallian transgression of the Choptank sea covers all pre-existing Coastal Plain units in eastern Virginia and spreads far westward into the Piedmont up to a fault-bounded rising upland. B. Late Serravallian deposition partly fills the Choptank sea in the east, and fluvial-deltaic deposits spread eastward across the Choptank marine deposits from a rising fault-bounded upland within the Piedmont. C. Choptank sea retreats eastward, and a reactivation of fault motion occurs along the Thornburg Scarp and the future position of the Tidewater Fall line. D. Late Pliocene Yorktown sea spreads westward up to the Thornburg Scarp, largely reworking the Choptank and older marine sediments east of the Thornburg Scarp and depositing its own sediments in their stead (after Weems and Edwards, 2007).

167 The Geology of Virginia than landforms on the succeeding surfaces. The result in the and equivalent high-stand marine units on the Delmarva Inner Coastal Plain is a deeply-dissected terrain with long linear Peninsula, range from 62 to 39 ka (MIS 3) (Scott, 2006; Mallison interfluves, locally called “necks.” The parallel entrenched et al., 2008; Parham et al., 2010). In paleo-valleys tributary to the rivers evolved into terrace-filled valleys seen in the modern Potomac River, transgressive estuarine deposits produce OSL topography. ages between ~90 ka and ~32 ka (Pavich et al., 2010); Parham et al. (2010) report highstand deposits of similar age in the Middle Coastal Plain geomorphology Roanoke/Albemarle drainage system in North Carolina. These dates span a time when eustatic sea levels were more than 20 m The region between the Surry Scarp and the Suffolk Scarp (66 ft) lower than present, according to sea-level curves based is capped by late Pliocene-early Pleistocene shallow marine and on coral dates (see Scott et al., 2010). The apparent discrepancy regressive deposits (falling-stage systems tract) of the Windsor between expected and apparent sea levels during MIS 3 may be Formation (Mixon et al., 1989). Surfaces atop these deposits resolved by invoking large and long-lasting peripheral bulges display less local relief than older, higher surfaces west of marginal to the Laurentide ice sheet. If these luminescence dates the Surry Scarp. Excavations and other ephemeral exposures are correct, they may indicate that after the glaciation of MIS 6, reveal weathering profiles that are generally shallower and less land-surface descent during the forebulge collapse lasted several complex than those developed in older, higher deposits. Still, tens of thousands of years. In addition, because the last glacial surficial expression of depositional features from the marine maxima of MIS 2 is less than 20 ka, southeastern Virginia and regressional environment is not exceptional or particularly northeastern North Carolina may still be sinking to the elevation noticeable. Perhaps during the long series of Pleistocene cold that exists at times when the regional glacial forebulge is fully climate events, the upland flats were poorly vegetated and relaxed (Scott, 2006; Mallison et al., 2008; Scott et al., 2010). susceptible to wind deflation and scour. Small zones of karst The presence of high-stand coastal zone deposits and topography disrupt Middle Coastal Plain surfaces at locations landforms on the Outer Coastal Plain signify periods with where locally-thickened marine shell beds in Pliocene deposits warm interglacial conditions, but on top of those deposits lie succumbed to deep solutional weathering (e.g., Johnson, 2008). scattered sand dunes and Carolina bays formed well inland of Below the Windsor uplands, largely preserved as high, the coast, relicts of colder, windier regional climates. On the inset terraces of the tidewater rivers, sit several Pleistocene Delmarva Peninsula in Virginia, elliptical swamps occur within transgressive/regressive sequences. The most extensive include sand-rimmed Carolina bays. Bliley and Pettry (1979) suggested the terraces underlain by the Charles City Formation at about 25 multiple generations of the mud-floored bays formed there on m (82 ft), thought to be approximately 0.5 Ma, possibly Marine broad interfluves as wind and waves repeatedly altered poorly- Isotope Stage (MIS) 9 or 11, in the James and the Potomac drained sites. Farther south across the Carolinas and Georgia, River estuaries; and the Shirley Formation underlying terraces numerous studies also report that Carolina bays and their rims at 12-15 m (40-50 ft) (180 ka; MIS stage 7) (Mixon et al., 1989). formed and stabilized repeatedly during the late Pleistocene. These deposits and those that are younger are constructional Most authors attribute the features to a combination of eolian landforms associated with the paleogeography of the evolving and shoreline processes operating around lakes (e.g., Grant et proto-estuaries. al., 1998; Ivester et al., 2003, 2004, 2007; Zanner et al., 2003; Wright, 2007), open-water bodies that mostly formed during Outer Coastal Plain geomorphology cool episodes with lower evapotranspiration rates. To the north, suites of arcuate dunes, bay rims, and wind-eroded ridges also Eastward of the Suffolk Scarp are extensive assemblages occur in the and Delaware counties of the Delmarva of low terraces – abandoned marine and estuary bottoms - that peninsula where they, too, appear to be a cold-climate overprint range from 10-1 m (33-3 ft) above sea level. These terraces to the Pleistocene terrace geomorphology (Denny and Owens, typically display bars, spits, barrier islands, inlets, and other 1979; Newell and Clark, 2008; Markewich et al., 2009, 2010). depositional landforms. Their sediments are part of the Tabb Formation and include the Sedgefield, Lynnhaven, and Poquoson RECENT STUDIES OF LANDSCAPE EVOLUTION members. Depositional surfaces of the Sedgefield member range in elevation from 6-10 m (20-33 ft). Uranium-series dates Mills et al. (1987) and Mills and Delcourt (1991) from corals average 71 +/- 7 ka (Wehmiller et al., 2004; Scott provided thorough reviews of landscape evolution studies et al., 2010); this time corresponds to the MIS 5e sea level high across the Appalachian highlands. Mills et al. (1987) gave a stand. The toe of the Suffolk Scarp, commonly about 5 m (16 historical synthesis of several long-studied geomorphic topics ft) elevation, represents the upward limits of the Lynnhaven including the evolution of Appalachian landscapes as viewed member. The Poquoson member lies 2 m (7 ft) or less above by proponents of W.M. Davis’s “cycle of erosion” versus J.T. sea level and the rising sea level presently erodes and Hack’s “dynamic equilibrium”; the significance of tectonics drowns many of its features. Similar terrace sequences occur and climate in regional denudation; and mechanisms of stream both on the Bay side and Atlantic side of the Virginia counties on terrace formation. They also reviewed more recent studies into the Delmarva Peninsula (Mixon et al., 1989; Scott et al., 2010). the development of saprolite and the climatic interpretation of Terrace treads preserve not only a record of fluctuating debris fans and other slope deposits (Mills et al., 1987). Mills and global sea levels but also evidence of regional glacio-isostatic Delcourt (1991) reported on a broad range of studies explaining adjustments and regional climatic alterations. Luminescence Quaternary geologic features, including several projects in dates from the Poquosin member in Virginia and North Carolina, Virginia that investigated saprolite, alluvial fans, debris fans,

168 Chapter 11: Landscape Evolution in Virginia hillslope processes, and colluvium. In their prescient summary, and sustained climatic and tectonic processes. Mills et al. (1987) cited a need for improved techniques for chronological control and correlation of deposits, more mapping, Legacy Sediment in Virginia sedimentological analyses to infer depositional processes, and greater attention to deposits on terraces and footslopes. Floodplains, lakes, and estuaries in Virginia contain Walker and Coleman (1987) and Colquhoun et al. (1991) distinctive (commonly ~1 m (3 ft) thick) amounts of sediment contain succinct summaries of Coastal Plain deposits and that archive centuries of human activity. Most of these deposits processes through time. The descriptions of Coastal Plain resulted from enhanced rates of soil erosion and sediment deposits in Virginia described in Colquhoun et al. (1991) expand transport following the onset of widespread and intensive farming, the discussion provided by Mixon et al. (1989) on their map of timbering, mining, and/or construction. Across Virginia, older the Virginia Coastal Plain. As a group, these works document sites with alluvium, slope deposits, and wind-blown sand sheets the timing of sea level transgressions and regressions, the may include deposits of legacy sediments that preserve early resulting formation of ocean and estuarine shorelines, river human artifacts and indirect evidence of ancient human activity valleys, the depositional features related to each, and the effects far back into the early Holocene and late Pleistocene (e.g., of weathering and erosional processes on former depositional Gardner, 1977; McAvoy and McAvoy, 1997). Legacy sediments surfaces. formed during extended periods of accumulation also can The following section provides a review of studies in preserve records of the impact of climate change. Deforestation Virginia related to landscape evolution, most of which extend can induce significant soil erosion and subsequent down-slope the work on the topics discussed by Mills et al. (1987), Mills deposition. From classical times to the present, astute observers and Delcourt (1991), and Colquhoun et al. (1991). In the two around the Mediterranean documented that soil denudation and decades since these earlier reviews, many of the recent advances sediment accumulation followed the loss of forest and other in geomorphology resulted from new technologies that markedly protective cover (Marsh, 1864; Knapp, 1997; Newell, 2004b,c; improved the ability of geologists to date geomorphic surfaces see also Herodotus, 2005). In Virginia, deforestation and soil and surficial deposits. Use of accelerator mass spectrometers erosion due to farming instigated widespread impacts, some of (AMS) permits identification of just a few atoms of stable and which began before European settlement. The arrival of corn unstable isotopes. Two results of this technique are the expansion agriculture from the southwest and Mississippi Valley around of the range of calculated radiocarbon dates to approximately 70 900 CE may have been responsible for the earliest agriculturally- ka, and the use of samples that weigh less than a gram. Another generated sediment, particularly from soils eroded during the AMS application measures concentrations of cosmogenic transition from forest to open-canopy environments created by radionuclides (CRN) which accumulate on geomorphic surfaces slash–and–burn corn farming within the emerging Algonkian with suitable exposed rock or soil profiles and uses those values confederation. to calculate the rate of surface erosion, stream incision, and other The subsequent practice of growing crops for export geomorphic processes. The accumulation of 10Be in soils or bare expanded the extent and range of soil erosion and altered estuaries rock surfaces, for example, allows determination of exposure soon after. The history of tobacco production in colonial times ages of over a million years (Bierman, 1994). An additional parallels the saga of soil erosion and depletion (Craven, 1926). new dating technique, already mentioned in previous sections, Many small tobacco ports throughout the Chesapeake system stems from procedures to measure the potential luminescence in Virginia and Maryland failed over time due to deposition of that accumulates due to electron displacement caused by alpha- sediment loads stripped from upland sources. The sediment- decay of uranium in sand grains after they are buried. Thermal- filled and abandoned ports of Joppa Towne, Port Tobacco, and and optically-stimulated luminescence procedures (TL and Bladensburg in Maryland are now on essentially dry land or OSL, respectively) permit dating of dunes, alluvium, loess, flood plain, as much as a kilometer from the head of tideon and other sediments in excess of 100 ka. Analyses of apatite their respective streams. In Virginia, Alexandria, Occoquan, in crystalline rock reveal patterns of regional exhumation in Dumfries, and other ports on tributaries of the Potomac were mountain belts. These thermochronometry techniques evaluate similarly effected, as were individual landings of old plantations radiogenic helium ((U-Th)/He) decay and fission track annealing along the major tributaries of the Rappahannock, York, and to calculate the cooling history of rocks as overburden above is James Rivers. Generally such sites of deposition in each estuary removed by erosion (Naeser, 1979; Zeitler et al., 1987). These extend from the fall zones of the rivers, through the fresh-water new radiometric dating techniques, along with improved criteria tidal portions of the rivers, and out to the limits of the zone of for establishing relative ages of deposits, allow geologists to maximum turbidity. At these zones the salinity is sufficient to measure the rates of terrestrial processes and solve landscape flocculate even the finest clay size particles (e.g., Langland and evolution questions not answerable earlier. Cronin, 2003). As discussed below, recent geomorphic studies in Virginia In the Piedmont and Coastal Plain provinces throughout that contribute to our understanding of landscape evolution eastern North America, toe slopes and floodplains of streams in examine landforms and deposits generated over many different watersheds impacted by agriculture now store post-settlement time scales. The youngest features are the most abundant and alluvium (Trimble, 1974; Costa, 1975; Ambers et al., 2006). commonly reveal the effects of human activity and can be Mill ponds trapped much of this sediment. During the 18th sensitive to relatively rapid climate changes. Although erosion and 19th centuries, streams in areas of industrial activity that and burial ensure that the oldest landscape remnants are often were dependent upon water power experienced significant sparse and hidden, they often provide insight into deep-seated alteration caused by thousands of dams. Walter and Merritts

169 The Geology of Virginia

(2008) report that dams impounded flow along approximately Studies of legacy sediments in Virginia provide insight 70% of streams in portions of southeastern Pennsylvania. Many into the impacts of sediment deposition and history of erosion. counties in Virginia in the mid-1800s also had numerous dams, Deep cores collected by the U.S. Geological Survey aboard most of which are now difficult to locate. Depending upon the the Marion-Dufresne (a French oceanographic ship) in the height of the millrace, each dam had the potential to create a deepest parts of the Chesapeake Bay, near the mouths of the sediment wedge kilometers long and several meters thick on its Potomac and Patuxent Rivers, provide a continuous record of downstream end (Walter and Merritts, 2008). sedimentation ranging from basal, sub-aerial outwash, deposited Urbanization, especially with expanding suburban housing during the last glacial maximum, to the present accumulations and road network construction following World War II, induced of bay mud (Cronin, 2000, and additional cores collected during an additional pulse of sedimentation along stream systems. Areas the Marion-Dufresne Picasso Cruise of 2003, unpublished converted from agricultural land to urban/suburban environments data). Legacy sediments are a recognizable but relatively thin commonly experience some degree of reforestation, but the component at the tops of cores from the Bay. Significant modern new paved surfaces and lawns shed far more water and less sedimentation into the Bay is confined to the upstream reaches sediment than agricultural land. As a result, stream channels of each tidewater river; it culminates in the zone of maximum must accommodate significantly less sediment load and higher turbidity in each tributary (Newell et al., 2004a). Estuary peak flows following rainfall. Under these conditions, streams systems in close proximity to extensive land clearing and build- commonly incised their beds. Many of these Piedmont and out of urban/suburban environments since the end of World Coastal Plain streams now flow in narrow valleys entrenched War II, such as tributaries to the Potomac in northern Virginia, into fine-grained legacy sediment (Wolman, 1967, 1987; Costa, experienced rapid sedimentation during the last century. Higher 1975; Jacobson and Coleman, 1986). on the source terrain in Virginia, toe slope deposits below The present-day erosion of many Virginia streams into their deforested hillsides can bury wetlands and archeological sites. beds and banks indicates that parts of these fluvial systems are Ambers et al. (2006) used such sediment records to reconstruct in disequilibrium. It may take decades, centuries, or longer for the land-use history of farming and reforestation at a site in the these over-steepened stream reaches to reshape their gradients eastern Blue Ridge that began as a colonial-era settlement. by scour and fill until they reach a new geomorphic stability Detailed studies of the history and impact of soil erosion (e.g., Harbor et al., 2005; Frankel et al., 2007; Leigh, 2010). In and sediment deposition may indicate that modern processes that time, vast amounts of fine-grained sediment, now stored in operate on a landscape still recovering from past geomorphic floodplains and low terraces and behind dams slated for removal, perturbations. For example, in Westmoreland County, an will pass to the lower tributaries and estuaries of the Chesapeake area of steep local relief in the Coastal Plain of northern system. Virginia, Newell et al. (2005) described surficial deposits and a The erosion and transport of fine-grained stream sediments geomorphic system that has episodically weathered, moved and pose problems to many parts of the ecosystem. In addition stored sediments since the Pliocene. Additional unpublished to limiting light for photosynthesis, particles in turbid water studies of Holocene sediment there indicate vigorous erosion convey nitrogen, phosphorous, organic carbon, residues from during the Late Glacial Maximum stripped surficial horizons pharmaceuticals, and other organic pollutants (e.g., Langland from deep Pliocene soil profiles and redistributed deposits and Cronin, 2003). Excessive amounts of such pollutants on lower gradient slopes. During the Holocene rise of the can destroy benthic habitats and profoundly disrupt life cycle Chesapeake Bay, erosional systems were relatively quiescent, processes. Existing basin-wide approaches to improving but starting during the Colonial period aggressive stripping and Chesapeake Bay water quality by reducing soil erosion and re-deposition of sediment carpeted flood plains and local tidal downstream sedimentation employ multiple sets of regulations estuaries. Cores taken in the estuaries commonly show basal on soil conservation, storm-water drainage management, erosion fluvial beds with wood and peat ranging from 4000-6000 yrs BP and sedimentation controls, riparian buffer zones, wetland from depths of 6-9 m (20-30 ft) below present sea level. These preservation, and stream restoration. sub-aerial deposits are overlain by sequences of estuarine muds Stream restoration projects commonly attempt to improve that include rangia, oysters, and clams tolerant of increasing several aspects of a degraded floodplain ecosystem, including a salinity. Rates of accumulation during the anthropogenic era now reduction in sediment loads and reestablishment of hydrologic exceed twice the rate of pre-settlement sedimentation. Sediment and ecologic interactions throughout the riparian zone. These stripped from the slopes and uplands of Westmoreland County projects typically use a variety of bank and channel stabilization during the late Pleistocene—the previous major deep erosional techniques (e.g., Rosgen, 1996). Experience gained by period—remains stored on the lower slopes and flood plains of geomorphologists trying to improve the success rate of such the sub-aerial terraces of the estuaries and their tributaries (W.L. restoration projects continues to stimulate discussion about the Newell, unpublished data). evolution of geomorphic, geochemical, and ecologic processes Similar landscapes do not always have identical histories. in fluvial systems (e.g., Montgomery and Buffington, 1998; In contrast to Westmoreland County, Virginia, studies of high- Bricker et al., 2004; Rathburn et al., 2009). Sites most difficult resolution LiDAR images in Worcester County, Maryland, to stabilize include those strongly influenced by geomorphic directly across the Chesapeake Bay, revealed complex macro- factors outside of the restored reach, particularly upstream patterns of dunes, rimmed depressions, and other landforms on hydrologic changes due to urbanization, and waves of erosion low-relief terraces and upland surfaces. The survival of these and sedimentation pulsing though the basin due to long-term or subtle surface features after 10 millennia or more of exposure episodic geomorphic instability (e.g., James et al., 2009). indicates that very little surface modification and erosion have

170 Chapter 11: Landscape Evolution in Virginia occurred on these uplands since the end of the Pleistocene (Newell and apparent landforms formed under periglacial climates. and Clark, 2008). The period of post-agricultural sedimentation Whittecar and Ryter (1992) mapped 10 long, narrow blockfields in the Pocomoke system may have been of short duration (boulder streams and blockslopes) along a 3 km (2 mi) section during land clearing. Wind transport was effective during early of the Blue Ridge in central Virginia. Using criteria developed agricultural exposure. However, the surfaces are generally too by Mills (1988) and others, they concluded that the landform gentle for transport of slope deposits and the initiation of fluvial shape, landscape setting, boulder fabrics, and presence of near- erosion during the absence of significant, routine freeze-thaw vertical tabular boulders (Figure 5A) indicated a periglacial climatic events. Extensive networks of drainage ditches and origin for these boulder streams. Zamkotowicz (1997) mapped straightened stream channels have been maintained for many boulder streams in four Virginia landscapes widely spaced along decades. In the modern agricultural environment of Worcester the Blue Ridge and noted that the numerous near-vertical slabs County, sediment transport is minimal. were positioned either parallel or perpendicular to the boulder stream sides. He concluded that differential motion within Periglacial Processes and Landforms actively moving boulder streams caused zones of both shearing and compression that positioned some boulders at very high The periglacial conditions that characterized much of the angles (Zamkotowicz, 1997). Similar trends of clast orientation Wisconsinan glacial period (71–10 ka) (Richmond and Fullerton, exist at Blackrock summit in the Shenandoah National Park, 1986) altered landscapes across Virginia. Landforms developed where quartzite boulders exhibit an open framework fabric under climates colder, drier, and windier than present conditions and orientations of long axes preferentially aligned downslope exist in a wide belt south of the Pleistocene glacial margin (Eaton et al., 2002). across much of New Jersey and Pennsylvania (Braun, 1989); Several studies estimated regional gradients in paleoclimatic and many of them provide evidence of discontinuous permafrost conditions along the Blue Ridge. Delcourt and Delcourt at those sites (Pewe, 1983; Newell and Wyckoff, 1992; Newell (1985) noted that the lower limit of elevation for polygonal et al., 2000; French et al., 2007; Newell and DeJong, 2011). landforms – indicators of permafrost – decreased northward in Clark and Ciolkosz (1988) and others reviewed reports of the Appalachians; the data they compiled reflected a regional similar landforms present at scattered locations along higher gradient of approximately 1.4 m/km (7.4 ft/mi). Zamkotowicz elevations of North Carolina, Virginia, and Maryland, including (1997) noted a state-wide gradient (3.0 m/km (15.8 ft/mi)) in widespread features in places on the Maryland Piedmont upland the elevation of the lower limit of boulder stream formation, (Cleaves, 2000). In recent years, the discoveries of even more estimated as the lowest elevation of a valley head that contained examples of periglacial landforms in the Appalachian highlands a boulder stream in that area. Nelson et al. (2007) calculated of Virginia confirm that relict landscapes dominated by strong a regional trend along the southern and central Appalachians frost shattering and ice-enhanced slope processes are ubiquitous of 1.42 m/km (7.5 ft/mi) based on mid-stream elevations of along high ridges from the Catoctins south to the Smokies. blockfields identified from aerial images and confirmed on These studies, described below, suggest that discontinuous foot. The variations in these three estimates of the proxy for permafrost probably existed along much of the Blue Ridge crest. a paleoclimatic gradient along the Blue Ridge have yet to be Even though year-long ground-ice may not have persisted long resolved, but may stem from differences in site-selection elsewhere in Virginia, frost-shattering, deflation, and related method, in the response of different rock types to frost action, or processes left their mark. Many recent studies of streams that from other local variables. head in the Piedmont and cross the Coastal Plain conclude that Only a few studies describe landforms or sediments in the the Piedmont experienced frost action sufficiently widespread Virginia Piedmont that indicate strong frost-driven processes and severe to generate bedload-dominated channel features during the Pleistocene, although such deposits occur in states to formed during the late Pleistocene (e.g., Leigh et al., 2004). The the north and south. Using field and laboratory evidence of loess, drier and windier conditions of that time also generated local colluvium, stone lines, and saprolite distribution at a site in the dunes and loess sheets. Piedmont of northern Virginia, Feldman et al. (2000) inferred Ridge crests and high meadows of the Shenandoah National that a significant period of surface erosion, and colluviation Park in central Virginia contain landforms and sediments formed of loamy sediment farther downslope, occurred between loess under periglacial conditions. Litwin et al. (2004) concluded that deposition (13.8 ka) and cessation of periglacial conditions by the the dominant forest vegetation in Big Meadows, Shenandoah end of the Pleistocene. Stone lines below and within relatively National Park, fluctuated repeatedly between boreal and northern loamy colluvium are common in the Piedmont and Blue Ridge hardwood from 42-12 ka, with the coldest climates dominating (e.g., Stolt et al., 1994). Whittecar (1985) documented colluvial from 25.5-20.5 ka. Eaton et al. (2003a) described tors, balanced wedges with stone lines on Pleistocene(?) terrace remnants in rocks, blockfields and shallow sheets of coarse colluvium along the central Piedmont that may have had a similar history. Even the summit of the Blue Ridge in central Virginia. In that same though a gradient in the intensity of frost-enhanced processes area, Eaton et al.(2002) and Smoot (2004a, b) also documented probably existed across the region (e.g., Cleaves, 2000), the stratified slope deposits several meters thick, indicative of dearth of periglacial deposits and landforms discovered in central hillside stripping and reduced vegetation cover, formed during Virginia is puzzling. In the Maryland Piedmont, pavements and the Wisconsin glacial maximum. linear valley-fills made of boulders overlie gabbro saprolite; and Block fields that form in valleys downslope of talus Cleaves (2000) interpreted these to be periglacial landforms accumulations (e.g., Michalek, 1968; Potter and Moss, 1968; developed as accelerated surface erosion stripped the saprolitic Godfrey, 1975; Henika, 1981) may be the most abundant matrix surrounding corestones. Farther south in western South

171 The Geology of Virginia

Carolina and North Carolina, several workers reported valley- A fills at sites high in Piedmont watersheds that contained churned soils or thick diamictic organic-rich colluvium in association with fossil or pollen records indicative of cold climatic conditions (Eargle, 1940, 1977; Overstreet et al., 1968; Whittecar, 1988). Many streams draining the Piedmont and the Inner Coastal Plain during Wisconsinan cold periods carried larger and coarser bedload than at present. Leigh et al. (2004), Leigh (2008), and Riggs and Ames (2008) documented examples of the low-sinuosity channel features that formed in these streams in Georgia and the Carolinas during MIS 4-2 (71 - 10 ka). In Virginia, Pleistocene terraces with large braid plains exist on the Nottoway and adjacent rivers. Along the Mattaponi and other rivers north of the James, such terraces are less prominent, but fill relatively straight valleys on their lower reaches formed during the late Pleistocene (e.g., Whittecar et al., 2000). Many authors presume that this abundant coarse sediment was generated by significant frost action during the Pleistocene, and delivered by streams then or later, perhaps during periods with an overall flashier hydrology than exists today. The windy and relatively dry conditions during the Wisconsinan glacial periods left a legacy of loess, dunes, and related features. The loess deposits described by Feldman et al. (2000) near Woodbridge, Virginia date from 13.8 ka, and may be related to deflation from floodplains on the glacial-age Potomac River. Wah (2003) reported widespread loess deposits incorporated into soil profiles on the Eastern Shore of Maryland; archeological evidence suggests eolian silt deposition lasted a few thousand years starting soon before 10.5 ka (Lowery and Custer, 1990). Other rivers in Virginia provided the sediment B source for dunes deposited on low terraces downwind of their floodplains. The late Pleistocene Cactus Hill archeological site sits on one such dune (McAvoy and McAvoy, 1997; Feathers et al., 2006). Mixon et al. (1989) mapped a sizeable dune field on the Nottoway River that straddles the state border; larger dune complexes in Georgia and the Carolinas formed in similar settings during the Wisconsinan (Markewich and Markewich, 1994; Ivester et al., 2001; Markewich et al., 2010). Carolina bay rims formed by wind are often attributed to periglacial conditions, too, in both Georgia and South Carolina (e.g., Ivester et al., 2004) as well as in Virginia (Bliley and Pettry, 1979), Maryland (Denny and Owens, 1979; Newell and Clark, 2008) and New Jersey (Newell et al., 2000; French et al., 2007; Newell and DeJong, 2011). Future analyses of eolian deposits in the Piedmont and Coastal Plain may illuminate the timing, persistence, and intensity of dry, windy episodes and the effects Figure 5. A. Near-vertical tabular clasts in a linear blockfield (boulder stream) near the Blue Ridge crest, Augusta County, Vir- ginia. View is uphill, parallel to the long axis of the blockfield. Nu- merous near-vertical boulders indicate a history of strong frost- heave. According to Zamkotowicz (1997) clasts such as these, aligned parallel with the axis and sides of the blockfield, reflect shearing caused by differential downhill velocities within the blockfield; those aligned perpendicular to slope direction form in zones of compression on the downhill end of moving masses in the blockfield. Photo credit: G.R.Whittecar. B. Debris flow de- posit from Lower Kinsey Run, Madison County, Virginia. Organic peat deposit (C) dated 34,770+690 BP is overlain by two debris flows (A and B) and fluvial sands (D) that were emplaced before 22,430+100 BP. The sedimentology and lithology of the debris flows indicates each originated from separate hollows. Scale is in decimeters. (from Eaton and others, 2003a) 172 Chapter 11: Landscape Evolution in Virginia of frozen versus thawed-saturated episodes during Pleistocene disintegrated granitic clasts (Eaton et al., 2003a). Comparison climatic oscillations. Deflated surfaces are more difficult to of these data with the relative age characterizations reported date, but given the preponderance of time in the Pleistocene by Youngblood (1998) suggests that the Nelson County fans thought to be dominated by periglacial processes (Braun, 1989), were deposited over a similar large range of ages. By the same relatively old surfaces may have experienced considerable loss criteria, weathered clasts and soils characterized by Whittecar of sediment by wind erosion, and by cryoplanation and related and Ryter (1992) on greenstone-rich debris-flow fans in Augusta slope movements over low-gradient surfaces (French, 2007). County formed during the Middle and Late Pleistocene, much more recently than the oldest fans identified in Nelson County. Alluvial and Debris-Flow Fans Radiocarbon analyses of multiple debris flows permitted several authors to discuss the recurrence interval of fan-forming Large numbers of both alluvial fans and debris-flow fans catastrophic rainfall events at individual sites in Virginia. Using cover toe-slopes in mountainous areas of Virginia (e.g., Clark, dates from Holocene debris-flow events in three fans within 1987; Kochel, 1987, 1990; Mills, 2000a). Alluvial fans contain Nelson County, Kochel (1987) calculated events recurred at a preponderance of gravel and sand beds deposited by upper- an average rate of 3-4 14C ka. Eaton et al. (2003b), working flow-regime or hyperconcentrated flow left by streams that drain in Madison County, dated eleven debris-flow events since 25 uplands rich in sandstone and quartzite. The largest formed where 14C ka, suggesting an recurrence interval of 2500 years. Data broad valleys or regional lowlands provided sufficient space to collected from a mastodon-bearing wetland deposit in Russell accommodate long-term accumulation (Mills, 2000a). Debris- County by Whittecar et al. (2007) indicated the site experienced flow fans typically consist of mud-rich diamicts deposited by three debris flows between 38 and 29 ka, suggesting a recurrence streams that drain mountainsides mantled by thin, stony soils interval of approximately 3000 years. The repeated occurrence with fine-grained matrixes. Rare and catastrophic rainfall events of debris flows during the middle and late Wisconsin and the that trigger slope failures generate high-velocity, high-viscosity Holocene may indicate that tropical air masses capable of causing flows which transport enormous boulders and poorly-sorted catastrophic rainfall dominated Virginia, not only during warm sediment onto toe-slopes (e.g., Clark, 1987; Kochel, 1987). The interglacial times, but also during short episodic periods during resulting fans may be smaller and steeper than alluvial fans, but otherwise cooler climatic periods (Whittecar et al., 2007). they are far more common (Mills, 2000b). As the following Debris flows, although episodic in frequency, transport studies report, both can form terraced complexes of sloping considerable volumes of coarse-grained regolith from steep remnant surfaces that record long histories of repeated cut- slopes to low-gradient streams in mountainous terrain (e.g., Hack and-fill by stream systems adjusting to changing geomorphic and Goodlett, 1960; Williams and Guy, 1973; Kochel, 1987, conditions. 1990; Jacobson et al., 1989; Miller, 1990). Studies of granitic Coalescing sets of alluvial fans lie along the western slopes landscapes (Eaton et al., 2003b) and those underlain by quartzite of the Blue Ridge tributary to the Potomac River. Composed (Sas and Eaton, 2008) in the Blue Ridge both suggested that the mostly of coarse quartzite gravel and sand, the fans mantle and mechanical load during episodic debris-flow activity represents armor shale and carbonate units. Whittecar and Duffy (2000) approximately half of the landscape denudation over the long- mapped fans in Augusta County near the Potomac-James divide term. using soil development criteria at well-drained sites and a quartzite-clast weathering scale. Comparisons of these soils and River Incision and Upland Erosion quartzite-cobble weathering with those from dated Coastal Plain deposits in Virginia indicate that the oldest fans may be Pliocene Mills (2000b) compiled rates of fluvial incision derived for or Miocene. Whittecar and Duffy (2000) suggested that largest streams throughout the eastern United States, and concluded and thickest fan deposits formed due to Miocene uplift while that rates likely increased across the region during the past two Pleistocene climate changes generated the younger valley-filling million years. The studies cited by Mills (2000b), including fans. three sites in Virginia, used a variety of techniques to establish Youngblood (1998) studied a fan complex in neighboring the ages of stream deposits including radiocarbon, stratigraphic Nelson County and suggested that alluvial surfaces on the correlation with glacial or marine sediments, paleomagnetic eastern side of the Blue Ridge formed due to tectonic and reversals in cave sediments, and U-Th content of flowstone. climatic conditions similar to those that influenced streams on the Several more recent studies used CRN on a variety of materials. western side of the Blue Ridge. The four alluvial surfaces in the In the New River valley, Granger et al. (1997) used 26Al and fan complex formed by Stoney Creek differ by geomorphic and 10Be from stream-transported quartz in cave sediments to obtain pedologic criteria, and by degree of greenstone-clast weathering an incision rate of approximately 27 m (89 ft) Ma-1. Hancock (Youngblood, 1998). and Harbor (2003) used 10Be dating of soils on terraces, as well Eaton et al. (2003a) reported radiometric ages for debris as magnetostratigraphy in cave sediments, to determine that fans in Madison County, Virginia based upon radiocarbon portions of the James River incised their bedrock channels at analyses on logs and 10Be cosmogenic data of the soil (Figure rates of 50-160 m (164-525 ft) Ma-1 during the past million years. 5B). Well-drained surfaces on the fans which were dated as less Beryllium-based techniques also helped Ward et al. (2005) show than 50,000 years old contained brown soils with only minor that the New River incised at an average rate of approximately 43 clast weathering. In contrast, the oldest surfaces, estimated to m (141 ft) Ma-1 but that during portions of the last 1 Ma, erosion be greater than 500,000 years old, contained soils with very rates as high as 100 m (328 ft) Ma-1 developed. During short high clay content (e.g., 72%), red matrix hues, and strongly periods coincident with the time of the last glacial maximum

173 The Geology of Virginia farther north (35-13 ka), the Potomac River incised at rates of Virginia are consistent with observations made in neighboring 0.8 m (2.6 ft) ka-1 (800 m (2625 ft) Ma-1), according to CRN states. Studies along the Green River, Kentucky (Granger et analyses made on bedrock strath surfaces (Figure 6) by Reusser al., 1997), in the New River gorge, West Virginia (Clifton and et al. (2004). These rates from Virginia-area streams agree with Granger, 2005), and across the Susquehanna River terraces and the overall long-term rates of erosion (approximately 30 m (98 surrounding Piedmont of the middle Atlantic margin (Pazzaglia ft) Ma-1) reported for the southern Appalachians (Matmon et al., and Gardner, 1994; Mills, 2000b) all document stream incision 2003). rates higher than hill-top erosion rates. Studies of summit-lowering rates suggest many upland surfaces in the central Appalachians degrade more slowly than Saprolite many stream channels. Hancock and Kirwan (2007) report ridge tops in eastern West Virginia affected by paleoperiglacial Saprolite mantles nearly the entire surface of the Piedmont weathering erode at approximately 6 m (20 ft) Ma-1. Ward et and Blue Ridge in Virginia and throughout the eastern United al. (2005) describe high terrace surfaces on the New River with States (Overstreet et al., 1968). Accordingly, the rate and timing erosion rates of approximately 2 m (7 ft) Ma-1. These rates fall of saprolite formation and its surface erosion significantly within the range of non-fluvial erosion estimates generated by influences our understanding of landscape evolution in Virginia. various studies in the region (e.g., Pavich, 1989; Bierman, 1994; Developed under warm, humid climates by chemical weathering Clifton and Granger, 2005). When compared with the fluvial of alumino-silicate minerals, saprolite has been forming in erosion rates discussed earlier, these slower summit-lowering Virginia for many tens of millions of years. The persistent rates suggest that the landscape relief across many parts of questions in Virginia’s saprolitized terrains involve the origin the Appalachians has increased over the past million years. and antiquity of upland surfaces and the ages of the underlying Hancock and Kirwan (2007) and Whitten and Hancock (2010) regolith. suggest that landscape disequilibrium and relief generation may Saprolite, the product of the isovolumetic weathering of now characterize the Appalachian landscape as it undergoes minerals (Pavich et al., 1985; Pavich, 1989) forms most readily adjustment to increased rates of fluvial incision driven by in igneous and metamorphic rocks (Figure 7A). Often 12-15 m climate changes. (39-49 ft) thick under stable hilltops in the Virginia Piedmont FigureMeasurements 6 ( half page) that suggest increasing relief in parts of (e.g., Pavich et al., 1989), saprolite develops as a geochemical

Figure 6. Bedrock terraces within Holtwood and Mather Gorges, and longitudinal profiles of the lower Susquehanna and Potomac Rivers. A. Terrace levels 1 and 3 in the middle of Holtwood Gorge along the Susquehanna River at low-flow conditions. Level 2 is not preserved at this location. At higher discharges, lower strath is inundated. A person is included in foreground for scale. B. View across Mather Gorge along the Potomac River at high flow (1700 m3/s (60035 ft3/s)). Well-defined strath terrace treads on both banks. Scale bar, 2 m (7 ft). C. Long profile of the lower Susquehanna River showing the location of Holtwood Gorge.D. Long profile of the lower Potomac River showing the location of Great Falls and Mather Gorge. m asl, meters above sea level. (from Reusser and others, 2004) 174

A Chapter 11: Landscape Evolution in Virginia A weathering front progresses downward where groundwater penetrates, altering minerals in bedrock to clay minerals and A hydrated oxides. The original rock fabric remains after most of the easily weathered minerals are weathered, but the major loss of mineral mass, promulgated by the transfer of solute load to groundwater, may produce saprolite porosities as high as 40% (Cleaves, 2000) (Figure 7B). In the upper 2-3 m (7- 10 ft) of the residuum, mechanical and chemical processes can create a seemingly structureless “massive zone” with increased density and lower porosity than the underlying saprolite (Pavich, 1989), although oriented clays and other soil microstructures can develop in these soil-saprolite transition zones (Stolt et al., 1994). In many settings, this massive zone is absent and the saprolite transitions upwards into transported regolith and pedogenic horizons. Saprolite thickness varies by landscape position and rock type. Both Costa and Cleaves (1984) and Pavich (1989) illustrated how saprolite usually thins along transects from Piedmont upland surfaces into stream valleys that have bedrock exposures in their channels. Incised channels in steep, small- order tributaries draining the upland commonly have not eroded their beds completely through the saprolite. In the Maryland Piedmont, Cleaves (2000) related differences in saprolite thickness to a combination of factors such as rock fractures and structures and the volume of weatherable minerals.

Mass-balance analyses of baseflow stream-water chemistry indicate that at its bedrock interface, saprolite can advance B downward at least 4 m (13 ft) Ma-1, and perhaps as much as 20 m (66 ft) Ma-1, under modern climatic conditions (Pavich, 1989); B presumably this rate of formation could have been faster when warmer and wetter subtropical climates prevailed in Virginia during portions of the Miocene and Pliocene (Poag and Sevon, 1989). Cleaves (2000) suggested that this rate would be 50-90% slower during most Pleistocene cold periods due to the cooler soil temperatures and reduced production of carbonic acid in the soil zone. Even with such conservative rate estimates, these studies suggest that many tens of meters of saprolite formed since the Miocene (perhaps the age of the oldest landscape remnants in the Piedmont; see Weems and Edwards, 2007). Hence, a geological conundrum – this thickness for saprolite is much larger than commonly observed in the field, even beneath protective terrace gravels of Miocene age (e.g., Pavich and Obermeier, 1985). Pavich (1989) suggested that the rate of saprolite production across the Piedmont during the Pleistocene has been matched by the long-term average rate of upland surface erosion, a balance needed for a landscape in dynamic equilibrium (Hack, 1960). This interpretation, supported by measurements of cosmogenic 10Be inventories, concludes that saprolite beneath upland surfaces is relatively young, between 1 and 5 Ma (Pavich, 1989). Oxygen-isotope ratios in kaolin suggest that saprolite in northern Figure 7. A. Photograph of a vertical exposure of soil and sap- rolite profile formed in granite gneiss, west of Fredricksburg, Vir- Virginia formed during climates cooler than present, additional ginia. Quartz vein and fracture pattern apparent in weathered evidence of a relatively young age for this regolith (Elliot et al., rock and saprolite. B. Idealized regolith profile on an upland 1997). Pavich (1989) argued that the principal mechanisms for underlain by an alumino-silicate rock and in an oxidizing envi- ronment. The massive subsoil zone is not present everywhere, lowering of the upland Piedmont surfaces involved removal and is usually related to rocks in which chemical weathering pro- of clay particles by surface wash and loss of volume and mass cesses produce smectite clay minerals. The shrink and swell during the formation of the soil and underlying saprolite. associated with alternate wetting and drying disrupts the struc- Regional uplift and down-to-the-coast tilting throughout the tured character of the saprolite. In places periglacial processes have disrupted the uppermost 1 to 3 m of the regolith profile Cenozoic also influenced stream incision rates, according to (modified from Pavich (1989) by Cleaves (2000)). Photo credit: Hack (1980) and Pavich (1989). W.L. Newell. 175 The Geology of Virginia

Other authors emphasize features that appear to have crater and the sub-surface structural trends of its annular fault formed by more episodic processes which generate landforms zone (Poag, 1999; Powers, 2000; Johnson, 2008). Even though during periods of disequilibrium. In Maryland (Cleaves and this narrow girdle with abundant numbers of high-angle faults Costa, 1979; Costa and Cleaves, 1984; Cleaves, 2000), upland may be a belt of minor historic earthquakes (Johnson et al., Piedmont surfaces of low relief are explained as the result of 1998), it is yet unclear if recent fault movements contributed to long-term landscape stability fostered by tectonic quiescence; the location or height of these scarps. and by chemical, rather than mechanical, weathering under Most late Cenozoic faults mapped in Virginia occur in the more tropical Miocene climates. Streams in these areas incised Coastal Plain, and particularly in the Fall Zone area where many valleys into the upland surfaces due to renewed regional uplift seem to influence stream patterns. Gremos (1992) used drilling and/or increased mechanical weathering caused by the shift records and lineament analyses to reconstruct the margins of to colder climates. Additional erosion on the upland surfaces fault-bounded crustal blocks which experienced a complex may have occurred due to periglacial processes during the pattern of uplift and subsidence during the Cenozoic. Reverse Pleistocene (Braun, 1989; Cleaves, 2000). Similar low-relief faulting dominated during the late Cenozoic (e.g., Mixon and upland surfaces, separated by steep-sided valleys, exist in the Newell, 1977; Dischinger, 1987; Prowell, 1988; Berquist and Piedmont of Virginia and may have origins similar to those Bailey, 1999; Bobyarchick, 2007), indicating a compressive described by Cleaves (2000); marine planation may also explain regime that may be driving uplift at present (Pazzaglia and the elevation and extent of some Piedmont upland surfaces, if Brandon, 1996; Spotila et al., 2004). the hypothesis proposed by Weems and Edwards (2007) proves The largest topographic break in Virginia - the Blue Ridge correct. Additional support for disequilibrium-related processes Escarpment – resembles a fault scarp, but recent analyses indicate comes from studies which demonstrate that relief along the it has an erosional origin (Figure 3). White (1950), Stose and Stose James and other streams in Virginia has increased during the (1951), and Hack (1982) suggested that the abrupt topographic Pleistocene due to stream incision rates that exceed the rates of rise between the western Piedmont and the rolling uplands of upland erosion (Mills 2000b; Hancock and Harbor, 2003). the southern Blue Ridge originated as a tectonic feature, either along a reactivated Mesozoic fault in the Brevard zone of North Tectonic Activity and Long-Term Erosion Carolina and Virginia or as a monoclinal flexure. Field evidence for localized tectonic activity along the escarpment remains Virginia forms part of a classic “passive margin” where few uncorroborated, and additional explanations proposed for the would expect to find geomorphic features attributed to recent asymmetric divide include erosional competition between tectonic activity. Easily missed because of their subtlety or drainage networks (Deitrich, 1959; Harbor, 1996; Harbor et al., breadth, such features do exist. Direct evidence of late Cenozoic 2000, 2005), lithologic controls on stream incision (Hack, 1973), tectonic activity include the small historic earthquakes in deep-seated tectonic anomalies (Battiau-Queney, 1989), and restricted areas such as the Central Virginia and the Giles County post-rifting migration of the scarp following rifting (Pazzaglia seismic zones (Bollinger, 1978); and the historically inactive and Brandon, 1996). Spotila et al. (2004) reviewed and tested faults that cut Cenozoic strata and regolith at several locations. these theories of scarp development using analyses of both (U- Broad regional uplift and tilting should be expected across the Th)/He and fission tracks in apatite grains collected from above Appalachian provinces due to isostatic rebound as denudation and along the Blue Ridge Escarpment and onto the Piedmont. unroofs the orogenic root, but the rate of rise and ruggedness in The dissimilar apatite cooling ages they calculated indicate some areas may require additional explanations (Spotila et al., that the southern Blue Ridge upland and the western Piedmont 2004). The post-orogenic forces driving late Cenozoic tectonic upland near the escarpment are not once-continuous erosional activity in Virginia may stem from sediment loading on areas surfaces now separated by a late Cenozoic fault. Instead their underlain by normal faults, intraplate compression, and uplift interpretation favored a “great escarpment” hypothesis. on peripheral bulges caused by both ice sheet advances and Thermal expansion and normal faulting along flanks of depocenter downwarping. continental rifts generates massive seaward-facing “great In Virginia, only a few reports describe geomorphic features escarpments” that persist along many passive margins long after formed along late Cenozoic fault zones. Saprolite displaced the thermal bulge cools and subsides (Ollier, 1985). Other types over terrace regolith along the Everona fault, located 45 km (28 of prominent escarpments may also form on the seaward side mi) west of Fredricksburg, and unusual topographic relief along of a flexural bulge formed along a margin impacted by post-rift neighboring faults suggest that the Paleozoic and Mesozoic faults sediment loading offshore (Keen and Beaumont, 1990). Pazzaglia along the Mountain Run system were reactivated during the late and Gardner (2000) identified the southern Blue Ridge front as a Cenozoic (e.g., “active fault” shown in Figure 4A, B) (Pavlides great escarpment that originated along a rift-flank and migrated et al., 1983; Prowell, 1988; Pavlides, 1994; Bobyarchick, 2007), to its present location, but was modified by late Cenozoic flexure but Quaternary activity there remains unproven (Wheeler, of the mid-Atlantic area. Spotila et al. (2004) agreed, noting that 2006). Marple and Talwani (2000) used multiple geophysical their apatite cooling ages fit the pattern recognized for other data sets and anomalous channel morphologies, cross-valley great escarpments on passive continental margins. terrace patterns, and valley shapes along Coastal Plain streams The recognition of the southern Blue Ridge front as a great to map an extensive buried fault system from earthquake-prone escarpment, combined with the results of geodynamical models Charleston, South Carolina into southeastern Virginia. Surface of the flexural effects caused by sediment loading of the offshore scarps along modern and Pleistocene estuary shorelines, as well continental margin, led Pazzaglia and Gardner (2000) to generate as belts of dolines, follow the rim of the Chesapeake Bay impact a comprehensive explanation of post-orogenic and post-rifting

176 Chapter 11: Landscape Evolution in Virginia landscape development for the middle Atlantic states. They of the down-warping. With the rise of the peripheral bulge, this noted that following the end of orogenic activity in the Permian, zone develops into a seaward-facing escarpment. Pazzaglia erosion removed more than 7 km (4.3 mi) of rock from the and Gardner (2000) contend this warping formed the Fall Zone Appalachians; according to fission-track thermochronology across the middle and southern Atlantic states. They also note studies in the Appalachian Basin to the west, most of it was that for models that simulated the peripheral bulge generated stripped from the Piedmont and Ridge and Valley to form a broad by the Baltimore Canyon Trough, the data indicate the adjacent low-relief surface by the end of the Jurassic (e.g., Boettcher Blue Ridge and Piedmont experienced up to 80 m (262 ft) of and Milliken, 1994). Mesozoic rifting of the Atlantic reversed uplift since the . In contrast, Braun (1989) calculated drainages from westward to eastward and created depocenters that in order to fill the offshore basins, an average thickness of at on the new continental margin. The largest is the Baltimore least 1.1 km (0.7 mi) of rock must have been eroded from all the Canyon Trough, a down-warped basin 18-km (11-mi) deep modern Atlantic watersheds from the Miocene to the present. and 400-km (249-mi) long that still collects sediment eroded The location of the depocenters and intervening structural from New England to Virginia (Figure 8). Depositional studies highs (e.g., the Norfolk Arch) on the continental margin, the indicate that at least three major pulses of sediment filled the strike and width of the physiographic regions, and the geometry basin – one in the Jurassic soon after rifting, another during the of the rifted margin resulted in notable variations in Virginia’s Cretaceous, and the latest that started rapidly during the middle landscape. Pazzaglia and Gardner (2000) argue that the Miocene and continues at a slower rate today (Poag and Sevon, pronounced subsidence of Baltimore Canyon Trough caused 1989; Poag, 1992) (Figure 9). As Pazzaglia and Gardner (2000) more marginal bulging in northern Virginia and Maryland than discuss, various authors have proposed tectonic, magmatic, and in southern Virginia and North Carolina. They think this flexure climatic processes to explain the timing of those pulses and the generated a Fall Line escarpment north of the Norfolk Arch that periods of quiescence between them. has more relief and is narrower than the broader Fall Zone found The weight of each rapid sedimentary onslaught apparently farther south. Uplift of the Maryland Piedmont upland induced both depressed basins on the continental shelf and slope, and more pronounced incision of streams there than across most of raised a broad peripheral bulge along the adjacent continental Virginia’s Piedmont (e.g., Hack, 1982). Differences between the margin. Pazzaglia and Gardner (1994, 2000) used geodynamic northern and southern portions of the Blue Ridge in Virginia also models, calibrated with geomorphic, sedimentologic, and appear to reflect these controls. Pazzaglia and Gardner (2000) stratigraphic data from the Susquehanna River system, to note that the southern Blue Ridge with its broad highlands, a illustrateFigure the flexure8. ( 1 generated column) on a 40-km (25-mi) thick continental divide that follows its asymmetric escarpment, elastic crustal plate by positive sedimentary loads offshore and and a lack of clear structural or lithologic control, lies at the negative erosional loads on the continent. The models suggest proposed zone of maximum peripheral bulge. It also lies that a zone of sharpest bending typically forms along the edge relatively far from the modest subsidence in the Carolina Trough

Long-term denudation Long-term deposition Salisbury Baltimore Canyon Central Appalachians Fall Zone Embayment Hinge Zone Ridge Trough Allegheny Great Blue Newark and plateau ValleyRidge Basin Valley Piedmont Coastal Plain ECMA 0

5

10

15

20

0 100 200 kilometers

Figure 8. Schematic cross-section across the Appalachian provinces and the Atlantic Coastal Plain and continental margin illustrat- ing major structural features and landscape relief (after Pazzaglia and Gardner, 2000).

177

F1gure 9 ( 1 column ) The Geology of Virginia

valleys – meandering and braided channels, flood plain deposits, higher terraces, eroded scarps – are the cumulative products of erosion, sediment transport, and storage from upstream reaches of each watershed. Although the patterns of hard rocks and fracture systems do influence local gradients and valley orientations, the physiography of the major valleys primarily reflects the transport and storage of water and sediment. Terrace ages and elevations are not identical for each great river system in Virginia. The highest fluvial terraces on the oldest river systems consist of fluvial-deltaic deposits formed at grade and merging with Miocene marine deposits along the inner edge of the Coastal Plain. Younger fluvial-to-estuarine terrace deposits in these systems are inset within valleys eroded into the Figure 9. Sediment flux history of siliciclastic detritus from the earlier, higher deposits. The distribution of the fluvial-estuarine New England and central Appalachians to the offshore basins deposits across the Coastal Plain defines the proto-valley of each of the middle Atlantic margin. Data compiled and modified from Poag and Sevon (1989) and Poag (1992) (from Pazzaglia and river and sets the template for putting boundaries in space and Gardner, 2000). time on the evolution of each contributing watershed. south of the Norfolk Arch. The narrow, northern Blue Ridge, In Virginia, the largest, oldest river systems that drain to in contrast, supports only small, isolated lower-relief uplands the Atlantic include the Potomac, the James, and the Roanoke along a structurally-controlled lithologic spine situated well Rivers (Figure 1). Each has breached the Blue Ridge and east of the continental divide and the proposed maximum bulge. now drains large areas of the Valley of Virginia and Ridge and Pazzaglia and Gardner (2000) contend that the proximity of the Valley physiographic provinces to the west (Figure 10). Near Baltimore Canyon Trough to the central Appalachian provinces the Coastal Plain margin the most ancient fluvial deposits and its greater degree of subsidence and flexure provided along the Potomac and James rivers are mapped as coeval with relatively high gradients to the Susquehanna, Potomac and the Miocene marine deposits of the Chesapeake Group in the James watersheds since rifting. This competitive advantage for Virginia Coastal Plain (Mixon et al., 1989). The oldest Roanoke these middle Atlantic drainages would have induced aggressive River deposits are somewhat younger, being equivalent to basin expansion, faster migration of the continental divide, and the Pliocene Yorktown Formation (Newell and Rader, 1982) destruction of any great escarpment north of Roanoke (Pazzaglia (Figure 11). The most ancient deposits for these three rivers, and Gardner, 2000). which occur as residual caps on hill tops, include distinctive The history of long-term erosion patterns and stream brown chert clasts from the regolith on the Paleozoic carbonates gradients in Virginia may match the regional story described in the Valley of Virginia. The Rappahannock River valley above, but important details may vary or never be known. Local also includes high, residual Miocene terrace deposits on the features, such as the Chesapeake impact crater, increased stream Piedmont adjacent to the Coastal Plain, but the deposits contain gradients and profoundly influenced drainage evolution in no Paleozoic chert, only resistant clasts from the Piedmont and Virginia. Furthermore, as we will discuss in the final section, we Blue Ridge rocks east of the Blue Ridge Mountains. Although can only document modern Virginia rivers history back to the an old river, the Rappahannock never breached the Blue Ridge. Miocene given the ages of the strata and erosional remnants still The smaller Atlantic draining rivers east of the Blue Ridge – the extant; thus we must be cautious if we project drainage patterns Mattaponi, the Pamunkey, the Appomattox, the Nottoway - all as we know them now back in time to the Mesozoic. have marginal marine affinities with younger Pliocene (Bacons Castle) and Pleistocene deposits. THE GREAT RIVER SYSTEMS To the west, beyond the Blue Ridge, the headwaters of the Potomac River and its major tributary, the Shenandoah The great valleys of the major rivers draining Virginia to River, drain the west slope of the Blue Ridge, the Valley of the Atlantic form extensive fluvial landscapes that are unique Virginia (largely Paleozoic carbonate rocks), and the Paleozoic physiographic domains. They are significant fluvial corridors, siliciclastic rocks of the Ridge and Valley. The watershed area pathways of water and sediment collected from large Appalachian of the Potomac beyond the Blue Ridge is the largest of the three watersheds and transported along and across the grain of the trans-Blue Ridge rivers in Virginia. Compared to the Ridge rock-controlled physiographic provinces. Downstream valley and Valley portions of the watersheds of the other two rivers, reaches of the major rivers contain the integrated effects of the the relief in the northern Valley of Virginia is generally lower landscape evolution within the watershed. Because these river and the expansive carbonate lowland is filled with enormous systems have been active for millions of years, their deposits volumes of surficial deposits and regolith. Much of the regolith and fluvial landforms contain the signatures of climate change is mineralogically mature, containing ore bodies of manganese, and tectonic processes that have occurred for shorter durations. iron, and kaolin (King, 1950). The Paleozoic carbonate rocks are The landforms of Virginia’s river valleys are largely artifacts covered with the insoluble residue that includes concentrations of the water- and sediment-discharge parameters generated by of chert nodules and re-precipitated chert, and lag deposits of each river’s tributary network. The most critical factors include resistant quartzite and sandstone cobbles and boulders from the the magnitude, duration, and frequency of flows, clast sizes, adjacent ridges of siliciclastic rocks. These materials, in situ and sediment volumes. Resulting landform assemblages in the and reworked, have been the major source of Potomac River 178

Fig. 10 (half page map – river breaching info) Chapter 11: Landscape Evolution in Virginia

Figure 10. Map of Virginia showing drainage basins of major river systems and the approximate crest of the Blue Ridge in northern Virginia and the Blue Ridge Escarpment in southern Virginia (dashed line). Notations indicate where the Potomac, James and Roa- noke rivers cross the Blue Ridge crest, and the geological period when each river breached the Blue Ridge and diverted drainage along more direct routes to the Atlantic Ocean.

fluvial deposits transported out onto the Coastal Plain since at to the northwest across the entire strike belt of the Ridge and least the Miocene (Naeser et al., 2004a, b; 2006). Likewise, Valley, through the Allegheny-Cumberland Plateau into the some of the surficial deposits on most elevated erosional Ohio River drainage system and thence to the Mississippi remnants in the Shenandoah Valley appear to be Miocene, based River and Gulf of Mexico. Speculation on the significance upon similarities in clast weathering with Coastal Plain deposits of this anomalous drainage pattern remains tenuous based on (Whittecar and Duffy, 2000). the results of known stratigraphic or structural frameworks Southward along strike, the same physiography/geology or tectonic models. From earliest days of geomorphology, it is drained by the headwaters of the James River. As discussed has been suggested that the New River represents an ancient earlier, several lines of evidence indicate that the James River drainage pattern superimposed and down-cut into an evolving in all three deformed-Appalachian provinces experienced long- landscape. However, many kilometers of rocks have been term valley entrenchment throughout much of the Pleistocene. removed since the Miocene and the system has destroyed most The westward limits of the James River watershed end at the top evidence of its earliest, pre-Cenozoic origins. Where the New of abrupt scarps cut into the terrains of the New River watershed River valley crosses the lower Paleozoic carbonate rocks, there to the southwest and the Potomac watershed to the northeast, are numerous high-level terraces with ancient gravel deposits in and scarps that transect the Paleozoic shale and carbonate rocks various states of weathering and karstification of the carbonate of the Valley of Virginia (Harbor et al., 2000). Even taller substrate (e.g., Mills and Wagner, 1985). It has generally been scarps formed in sedimentary rocks mark the Roanoke-New assumed that these terraces are analogs of the flights of terraces drainage divide near Blacksburg (Hancock and Harbor, 2003; in the Atlantic-draining rivers, and that they span a great age Harbor et al., 2005). The largest topographic break in Virginia, range from the Miocene to present day. However, cosmogenic the 300 m (984 ft) -tall Blue Ridge Escarpment, forms where dating of terrace deposits and stream gravels in caves in the New Roanoke River headwater streams actively incise into the Blue River valley indicates that even the most deeply weathered and Ridge upland, dismembering the network of the New River, and elevated deposits analyzed to date are Pleistocene (Granger et pirating flow towards the Atlantic (e.g., Dietrich, 1959; Hack al., 1997; Mills, 2000b; Ward et al., 2005). Flights of terraces in 1982; Prince and Henika, 2010a, b). the other large river systems must also be dated and compared The Roanoke River headwaters west of the Blue Ridge are to make regional sense of this possible indicator of uplift and much smaller than the James, and share a watershed boundary stripping history. with the southern boundary of the James River. The limited In , the Clinch and Holston Rivers flow incursion of the Roanoke River headwaters beyond the Blue within the strike valleys of the Paleozoic carbonate rocks as they Ridge and the younger deltaic deposits at the Coastal Plain descend to join the headwaters of the Tennessee River which margin in North Carolina together indicate a generally younger flows to the Mississippi. Local karst exhibits high relief (many history for the growth and down-cutting of the Roanoke River tens of meters) and the deposits of adjacent bounding mountain compared to the James and Potomac rivers. slopes are distributed into sinkholes and onto local terraces. This The New River watershed begins in the highlands in North watershed has preserved significant Pleistocene flora and fauna Carolina near Grandfather Mountain. The main valley trends remains in unusual, relatively protected alluvial settings (e.g.,

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Figure 11 ( 1 column ) Information derived from these methods can be used to test the validity and implications of fresh interpretive paradigms for the Virginia landscape. Furthermore, geomorphologists have just begun to understand the influences of the Chesapeake Bay impact crater and the Baltimore Canyon trough. They have yet to fully explore the influence cold climates had upon surface processes locally, or how interactions between glacial ice, lithospheric flexures, changing climates, and sea level fluctuations affected and will affect the mid-Atlantic region. Also, the demands of a growing population will accentuate the need to plan wisely for resource extraction, for waste storage, for ecosystem preservation, and for hazard identification. Increasing data-processing power and instrument miniaturization continue to improve research capabilities. As demonstrated earlier, one extraordinarily useful new technique for landscape studies, airborne Light Detection And Ranging (LiDAR), can provide topographic information of unparalleled detail efficiently for wide areas. Subtle landforms with relief as low as 10 cm (4 in) can be distinguished on maps interpreted from LiDAR data (e.g., Newell and Clark, 2008; Mallison et al., 2008; Riggs et al., 2008; Markewich et al., 2009). Detailed features can now be resolved including recently-active fault scarps, low-altitude terrace surfaces near sea level that are at risk from flooding during coastal storms, and landslide scars, slope deposits, flood plain and river channel changes resulting from catastrophic mountain storms. When these data are combined with satellite images, digital elevation models, and with field data located by Geographic Positioning Systems (GPS), scientists can generate powerful visualization tools. Subsurface information from improved seismic and radar profiling now provides detailed information on the stratigraphy and structure of shallow geologic materials. Improvements in coring and logging technologies available on ships, trucks, and portable units allow recovery of relatively undisturbed samples from increasingly greater depths (e.g., Figure 12). Advances in dating techniques, especially those using accelerator-based radiocarbon analyses, luminescence methods, and cosmogenic radionuclides, can be applied to a wide range of samples in many geomorphic settings. Figure 11. Sketch map emphasizing the sequence of develop- Similarly, fission-track dating of detrital sand grains from cores ment of the deltas and other regressive deposits across the Inner Coastal Plain of Virginia and neighboring states. Fluvial deposits can present new concepts for erosion rates. of the older two rivers with significant delta deposits (Potomac Application of these tools will permit significant progress in (Stage I) and James (Stage II)) are coeval with different Miocene the near future as geomorphologists and others study the history marine deposits on the Coastal Plain. The oldest fluvial depos- of landscapes in Virginia. We suggest four major areas of research its of the Roanoke River (Stage III) are correlated with Pliocene marine deposits (from Newell and Rader, 1982). The uplift and that need to be addressed: (1) the post-crater “unroofing history” depression depicted on this illustration were interpreted initially of the Appalachians; (2) the effects of cold, windy, and highly from the order of delta development and deeper river incision in variable climates during MIS 3; (3) the potential variability the northern part of the area shown. The timing, duration, and induced by rising and collapsing glacial forebulges; and (4) the cause(s) of processes in this area (e.g., bulging marginal to the Baltimore Canyon Trough (Pazzaglia and Gardner, 2000); glacio- identification of hazards and preservation of resources. isostatic flexures (Scott and others, 2010)) are topics for contin- A more detailed Cenozoic history of the denudation of the ued research. Appalachians waits to be deciphered from the upland regolith. McDonald and Bartlett, 1983; Wilkes et al., 1994; Whittecar et As we continue to learn the ages and origins of ancient regolith al., 2007). perched atop hills in that erosional terrain, those small remnants can be correlated to events represented by Cenozoic strata of the FUTURE RESEARCH Coastal Plain and continental shelf. Target deposits include the alluvial and debris fans that surround mountain masses in the In the next few decades, many advances in the study of Blue Ridge, the Valley of Virginia, and Ridge and Valley; the landscape evolution will originate from the present convergence stream gravels and low-relief surfaces present on both the Blue of rapidly developing technologies for creating images and maps, Ridge and Piedmont uplands, abandoned due to stream piracy for collecting and describing cores, and for dating samples. and divide migration; and the Piedmont’s loamy “Coastal Plain

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Figure 12 ( 1 column ) Chapter 11: Landscape Evolution in Virginia

caps” – numerous deeply-weathered soil bodies long recognized by soil mappers as forming on transported sediments, but present on uplands (W.L. Daniels, personal communication, 1983). Also, with a more comprehensive understanding of saprolite thicknesses and rates of production and stripping on different rock types, we can evaluate the effectiveness and extent of possible Miocene marine planation as well as the potential for soil erosion and sediment production in different basins. A similar understanding of the processes and history of chert- armored regolith on carbonate terrains is needed to evaluate the sequencing of unroofing events. Is there an equilibrium thickness of regolith below the chert-rubble armor, such that material removed from the surface is replaced at the bottom of the regolith by insoluble residue formed by leaching of the carbonate bedrock? Brown chert cobbles and pebbles present in Miocene Coastal Plain gravels suggest that such a process was actively creating a regolith in the Valley of Virginia before the Miocene. A better understanding of the ages of residual and transported regolith is needed for many tasks, including the capability to date movements on Cenozoic faults that cut these bodies. Recent studies indicate that colder temperatures and lowered sea levels were but two of the geomorphic controls driving processes throughout Virginia during the ~50 ka years of MIS 2, 3, and 4 but the importance of additional factors remains uncertain. According to the ice-core, ocean-sediment-core, and pollen records (Delcourt and Delcourt, 1981; Bond et al., 1993; Dansgaard et al., 1993), during MIS 3 (59–24,000 cal yr BP; Martinson et al., 1987) climates throughout regions in front of the Laurentide ice sheet oscillated between cooler-than-present and very-cold conditions, and many of those periods were relatively dry and windy. Climates switched markedly every few thousand years (Alley, 2000). The ice sheet thickening and thinning during these changes probably produced sea level changes repeatedly even while ocean surfaces were depressed many tens of meters below present elevation. At the same time, if Scott et al., (2010) and Mallison et al. (2008) were correct, the glacioisostatic peripheral bulge of MIS 6 had relaxed sufficiently so that the present-day coastal zone sat at ~-30 m (-98 ft), an elevation low enough to be inundated by the lowered ocean at least once during MIS 3. Thus, during MIS 3 four important geomorphic factors—hydrology and land surface elevation, as well as temperature and sea level—changed frequently or differed from present conditions significantly. However, the timing and interactions of the changing MIS Figure 12. Mid-Holocene storm surge deposit 0.4 m (1.3 ft) thick 3 conditions are poorly known. The Coastal Plain of Virginia preserved beneath 4 m (13 ft) of estuarine mud and surficial peat. The diamict contains Miocene Calvert Formation chips, contains a wealth of landscape features that may have formed woody clasts, sand and mud, an accumulation identical to the during MIS 3 that when dated and placed into their geomorphic half-meter-thick deposits which buried shingle beaches along context could be useful in determining the effects of various the Potomac estuary shoreline after cliff erosion generated by processes. Changes in evapotranspiration and in the intensity the storm bore of Hurricane Isabel (September 2003). A large woody clast in the middle of the photo dated at 6730 - 6310 cal and amount of precipitation probably influenced transitions yr BP. Measuring tape marked in tenths of feet. Vibracore was between braided-channel floodplains and meandering-channel collected with Hoverprobe 2000 in Currioman Creek, Westmore- flood plains of Coastal Plain rivers throughout the southeastern land County, Virginia about 10 m (33 ft) offshore from a wave-cut U.S., as well as the formation and in-filling of lakes in Carolina scarp. Similar deposits along many estuarine shores in Virginia may preserve records of large storm events. A unique system bay depressions. Dated loess sheets, dune fields and multiple developed by the U.S. Geological Survey, the Hoverprobe 2000 generations of Carolina bay rims in Virginia should provide can recover soft sediment cores from depths of 30 m (100 ft), evidence of dry and windy episodes. Eastern Virginia contains while operating in wetlands environments that cannot be ac- both shoreline features of MIS 3 age at 1-2 m (3.3-7 ft) elevation cessed by either boat or truck (Newell and Queen, 2000). Photo credit: W.L. Newell. and braided stream terraces, probably formed during MIS 3, that 181 The Geology of Virginia are graded to a base level below present sea level. Establishing ACKNOWLEDGEMENTS their ages and geologic relationships will assist in understanding the history of both sea level and glacio-isostatic adjustments. We gratefully acknowledge the inspiration and insights The Appalachian provinces may also contain MIS 3 deposits, shared by colleagues and students over many years during particularly in and under colluvial debris fans, periglacial valley vigorous discussions at field locations, particularly by colleagues fills in small-order streams, tufa mounds at springs and rapids, of the U.S. Geological Survey, the Virginia Division of Geology and speleothems and sediments within caves and dolines. and Mineral Resources, and the Southeastern Friends of the Many landscape studies stem from the needs to preserve Pleistocene. Nancy K. Pontier, Chuck Bailey, Cullen Sherwood, essential components of the ecosystem that supports human and Hugh Mills provided helpful reviews of the manuscript. activities, and to avoid hazards to life and property. During the coming decades the continuing spread of urban centers and REFERENCES CITED industrial activities across the watersheds and coastal zones of Virginia will drive a surge in the demand for evaluations Alley, R.B., 2000, The two-mile time machine: Ice cores, abrupt of modern and ancient landforms and geomorphic processes. change and our future: Princeton University Press, 229 p. Virginia watersheds generate different amounts and types of Ambers, R.K.R., Druckenbrod, D.L., and Ambers, C.L., 2006, sediment load based on their relief, rock type, weatherability, Geomorphic response to historical agriculture at Monument legacy sediment record, and land use history. In order to most Hill in the Blue Ridge foothills of central Virginia: Catena, effectively reduce stream sediment loads, planners need the v. 65, p. 49-60. results of a systematic assessment of the amount and type of Ator, S.W., Denver, J.M., Krantz, D.E., Newell, W.L., and legacy sediment stored on the slopes and floodplains of basins Martucci, S.K., 2005, A surficial hydrogeologic framework across the Chesapeake Bay watershed, and the potential of for the Mid-Atlantic Coastal Plain: U.S. Geological Survey those basins to release their loads. Also, the techniques used by Professional Paper 1680, 44 p. the burgeoning numbers of stream restoration efforts in those Bailey, C.M., 1999, Physiographic map of Virginia: http://web. watersheds should be evaluated for their long-term effectiveness wm.edu/geology/virginia/provinces/physiography.html in reducing sediment loads, as well as improving ecosystem (July 2010). functions of the riparian zones (e.g., Miller and Kochel, 2010). Battiau-Queney, Y., 1989, Constraints from deep crustal Because many of these projects aim to stabilize stream banks, it structures on long-term landform development of the will be important to assess the role of coarse sediment production British Isles and eastern United States: Geomorphology, v. and transport in maintaining in-channel habitat and the ecologic 2, p. 53-70. functions of hyporheic exchange through coarse-sediment beds Berquist, C.R., Jr., 1987, Minerals in high level gravel deposits and banks. Many of these restored stream segments lie within along the Fall Zone of Virginia: Virginia Minerals, v. 33, portions of drainage networks that may be undergoing long-term no. 4, p. 37-40. geomorphic adjustments; the sustainability of these designs Berquist, C.R., Jr., and Bailey, C.M., 1999, Late Cenozoic through time should inform the planning for future restoration reverse faulting in the Fall Zone, southeastern Virginia: projects. Journal of Geology, v. 107, p. 727-732. Virginia coastal zones need continuing studies of the Bierman, P.R., 1994, Using in situ produced cosmogenic isotopes sedimentary history layered within their estuaries and across the to estimate rates of landscape evolution: A review from the continental shelf. This information would contribute to solving geomorphic perspective: Journal of Geophysical Research, many existing and future problems. An accurate understanding v. 99, p. 13,885–13,896, doi: 10.1029/94JB00459 of the history of cliff erosion and the effectiveness of shore- Bliley, D.J., and Pettry, D.E., 1979, Carolina bays on the Eastern stabilization structures along upper reaches of Virginia’s Shore of Virginia: Soil Science Society America Journal, v. estuaries requires evaluations of the distribution and source of 43, p. 558-564. sub-bottom sediments. Significant storm surges and prehistoric Bobyarchick, A.R., 2007, Kinematics of the Everona fault, tsunamis can leave their traces in estuary and lagoon sediments central Virginia: Geological Society of America, Abstracts (e.g., Figure 12). The distribution of sandy aquifers and muddy with Programs v. 39, no. 2, p. 89. confining beds, both onshore and beneath estuaries and lagoons, Boettcher, S.S., and Milliken, K.L., 1994, Mesozoic-Cenozoic controls the discharge of freshwater into saline environments, unroofing of the southern Appalachian basin: Apatite fission and the intrusion of salt water inland caused by over-pumping of track evidence from middle Pennsylvanian sandstones: ground water. Farther out onto the continental shelf, such studies Journal of Geology, v. 102, p. 655-663. would be needed to choose safe sites for drilling platforms or Bollinger, G.A., 1978, Seismic hazards in Virginia: Virginia wind turbines and the pipes and cables connecting the rigs to Minerals, v. 24. no. 4, p. 29-34. shore facilities. Geomorphic and stratigraphic analyses in all Bond, G., Broecker, W., Johnson, S., McManus, J., Labeyrie, of these areas could also aid in understanding the history and L., Jouzel, J., and Bonani, G., 1993, Correlations between causes of long-term land subsidence and its impact on future sea climate records from North Atlantic sediments and level rise. Greenland ice: Nature, v. 365, p. 143–147. Virginia’s physiographic provinces offer fertile prospects Braun, D.D., 1989, Glacial and periglacial erosion of the for continued research into the integrated history of the evolving Appalachians, in Gardner, T.W., and Sevon, W.D., eds., landscape. Appalachian geomorphology: Geomorphology, v. 2, p. 233–256.

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Bricker, O.P., Newell, W.L., and Simon, N.S., 2004, Bog iron Bond, G., 1993, Evidence for general instability of past formation in the Nasawango watershed, Maryland: U.S. climate from a 250-kyear ice-core record: Nature, v. 364, Geological Survey Open File Report, OFR 03-346 (version p. 218–220. 1) http://pubs.usgs.gov/of/2003/of03-346 (July 2010). Delcourt, P.A., and Delcourt, H.R., 1981, Vegetation maps for Bryan, R.B., and Jones, J.A.A., 1997, The significance of soil eastern North America: 40,000 yr BP to the present, in piping processes: Inventory and prospect: Geomorphology, Romans, R.C., ed., Geobotany II. Plenum. v. 20, p. 209-218. Delcourt, P.A., and Delcourt, H.R., 1985, Dynamic Quaternary Buol, S.W., Amoozegar, A., and Vespraskas, M.J., 2000, landscapes of east Tennessee: An integration of paleoecology, Physical, chemical, and morphological properties of some geomorphology, and archaeology: University of Tennessee, regoliths in North Carolina: Southeastern Geology, v. 39, Department of Geological Studies: Studies in Geology, v. p. 151-160. 9, p. 191-198. Byrd, W., 1841, Westover Manuscripts: The history of the Denny, C.S., and Owens, J.P., 1979, Sand dunes on the central dividing line betwixt Virginia and North Carolina; A journey Delmarva Peninsula, Maryland and Delaware: U.S. to the Land of Eden, A. D. 1733; and A progress to the Geological Survey Professional Paper 1067-C, 15 p. mines. Written from 1728 to 1736, and now first published, Dietrich, R.V., 1959, Geology and mineral resources of Floyd Edmund and Julian C. Ruffin, Petersburg. County of the Blue Ridge Upland, southwestern Virginia: Clark, G.M., 1987, Debris slide and debris flow historical Bulletin Virginia Polytechnic Institute 134, 160 p. events in the Appalachians south of the glacial border, Dischinger, J.E., Jr., 1987, Late Mesozoic and Cenozoic in Costa, J.E and Wieczorek, G.F., eds., Debris flows/ stratigraphic and structural framework near Hopewell, avalanches: Process, recognition and mitigation: Boulder, Virginia: U.S. Geological Survey Bulletin 1567, 48 p. CO, Geological Society of America, p. 125–138. Dunford-Jackson, C.S., 1978, The geomorphic evolution of the Clark, G.M., and Ciolkosz, E.J., 1988, Periglacial geomorphology Rappahannock River basin [M.S. thesis]: Charlottesville, of the Appalachian Highlands and interior highlands south University of Virginia, 92 p. of the glacial border— A review: Geomorphology, v. 1, p. Dunne, T., 1980, Formation and controls of channel networks: 191–220. Progress in Physical Geography, v. 4, p. 211-239. Cleaves, E.T., 2000, Regoliths of the Middle-Atlantic Piedmont Dunne, T., 1990, Hydrology, mechanics, and geomorphic and evolution of a polymorphic landscape: Southeastern implications of erosion by subsurface flow, in Higgins, Geology, v. 39, no. 3-4, p.199-222. C.G., and Coates, D.R. eds., Groundwater geomorphology, Cleaves, E.T., and Costa, J.E., 1979, Equilibrium, cyclicity, the role of subsurface water in earth-surface processes and and problems of scale – Maryland’s Piedmont landscape: landforms: Geological Society of America Special Paper Maryland Geological Survey Information Circular 29, 32 252, p. 1-28. p. Eargle, D.H., 1940, The relations of soils and surface in the Clifton, T., and Granger, D.E., 2005, Erosion rate of the South Carolina Piedmont: Science, v. 91, no. 2362, p.337- Appalachian Plateau in the vicinity of the New River Gorge, 338. West Virginia: Geological Society of America, Abstracts Eargle, D.H., 1977, Piedmont Pleistocene soils of the Spartanburg with Programs, v. 37, no. 1, p. 18. area, South Carolina: Division of Geology Geologic Notes, Colquhoun, D.J., Johnson, G.H., Peebles, P.C., Huddlestun, v. 21, State Development Board, South Carolina, p. 57–74. P.F., and Scott, T., 1991, Quaternary geology of the Atlantic Eaton, L.S., Wieczorek, G.F., Morgan, B.A., McNown, A.W., Coastal Plain, in Morrison, R.B., ed., Quaternary nonglacial Smoot, J.P, and Litwin, R.J., 2002, Periglacial slope geology: Conterminous U.S., Geology of North America: v. processes and deposits in the Blue Ridge Mountains of K-2: Boulder, Colorado, Geological Society of America, central Virginia: Geological Society of America, Abstracts p. 629-650. with Programs, v. 34, no.1, p. 276. Costa, J.E., 1975, Effects of agriculture on erosion and Eaton, L.S., Morgan, B.A., Kochel, R.C., and Howard, A.D., sedimentation in the Piedmont Province, Maryland: 2003a, Quaternary deposits and landscape evolution of the Geological Society of America Bulletin, v. 86, p. 1281- central Blue Ridge of Virginia: Geomorphology, v. 56, p. 1286. 139–154. Costa, J.E., and Cleaves, E.T., 1984, The Piedmont landscape Eaton, L.S., Morgan, B.A., Kochel, R.C., and Howard, A.D., of Maryland; a new look at an old problem: Earth Surface 2003b, Role of debris flows in long-term landscape Processes and Landforms, v. 9, p. 59-74. denudation in the central Appalachians of Virginia: Geology, Craven, A.O., 1926, Soil exhaustion as a factor in the agricultural v. 31, p. 339-342. history of Virginia and Maryland, 1606-1860: University of Elliott, W.C., Savin, S.M., Dong, H., and Peacor, D.R., 1997, Illinois Press, Urbana, Illinois, 184 p. A paleoclimate interpretation derived from pedogenic clay Cronin, T.M., ed., 2000, Initial report on IMAGES V cruise of minerals from the Piedmont Province, Virginia: Chemical the Marion-Dufresne to the Chesapeake Bay, June 20-22, Geology, v. 142, p. 201-211. 1999: U.S. Geological Survey Open File Report 00-306, Erickson, P.A., and Harbor, D.J., 1998, Bringing down Floyd: 133 p. Incision by the James River in the Valley and Ridge of Dansgaard, W., Johnsen, S.J., Clausen, H.B., Dahl-Jensen, Virginia: Geological Society of America, Abstracts with D., Gundestrup, N.S., Hammer, C.U., Hvidberg, C.S., Programs, v. 30, no. 7, p. 142. Steffensen, J.P., Sveinbjornsdottir, A.E., Jouzel, J., and Feathers, J.K., Rhodes, E.J., Huot, S., and Mcavoy, J.M.,

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2006, Luminescence dating of sand deposits related to Hack, J.T., and Goodlett, J.C., 1960, Geomorphology and forest late Pleistocene human occupation at the Cactus Hill Site, ecology of a mountain region in the central Appalachians: Virginia, USA: Quaternary Geochronology, v. 1, p. 167– U.S. Geological Survey Professional Paper 347, 66 p. 187. Hancock, G.S., and Harbor, D.J., 2003, Knickpoint retreat and Feldman, S.B., Zelansky, L.W., Pavich, M.J., Millard, H.T., Jr., landscape disequilibrium on the James River from the 2000, Late Pleistocene eolian activity and post-depositional Piedmont through the Valley and Ridge, central Virginia, alteration on the Piedmont of Virginia: Southeastern USA: Eos (Transactions, American Geophysical Union), v. Geology, v. 39, p. 183-198. 84, p. Abstract H52A-1141. Frankel, K.L., Pazzaglia, F.J., and Vaughn, J.D., 2007, Knickpoint Hancock, G.S., and Kirwan, M., 2007, Summit erosion rates evolution in a vertically bedded substrate, upstream-dipping deduced from 10Be: Implications for relief production in terraces, and Atlantic slope bedrock channels: Geological the central Appalachians: Geology, v. 35, p. 89–92; doi: Society of America Bulletin, v.119, no. 3/4, p. 476-486. 10.1130/G23147A.1. French, H.M., 2007, The periglacial environment (3rd edition): Harbor, D.J., 1996, Non-uniform erosion patterns in the Chichester, U.K., John Wiley and Sons Ltd., 458 p. Appalachian Mountains of Virginia: Geological Society of French, H.M., Demitroff, M., Forman, S.L., and Newell W.L., America, Abstracts with Programs, v. 28, no. 7, p. 116. 2007, A chronology of Late-Pleistocene permafrost events Harbor, D., Bacastow, A., Heath, A., Rogers, J., 2005, Capturing in southern New Jersey, eastern USA: Permafrost and variable knickpoint retreats in the central Appalachians, Periglacial Processes, v. 18, p. 49-59. USA: Geographia Fisica E Dinamica Quaternaria, v. 28, p. Gardner, W.M., 1977, Flint Run paleoindian complex and its 23-36. implications for eastern North American prehistory, in Harbor, D., Erickson, P., Rittenhouse, D., Carlson, M., Gardner, Newman, W.S., and Salwen, B., eds., Amerinds and their T., Merritts, D., Dorale, J., and Panuska, B., 2000, Bringing paleoenvironments in northeastern North America: Annals down Floyd: Rapid erosion of the upper James River basin of the New York Academy of Sciences, v. 288, p. 257-263. in response to scarp retreat and basin capture, in Harbor, D., Gathright, T.M., and Frischmann, P.S.,1986, Geology of the ed., Landscape evolution in the upper James River Basin: Harrisonburg and Bridgewater quadrangles, Virginia: Lexington, Virginia, 2000 Southeastern Friends of the Virginia Division of Mineral Resources Publication 60, 21 Pleistocene Field Trip Guidebook, p. 31–47. p. Henika, W.S., 1981, Geology of the Villamont and Montvale Godfrey, A.E., 1975, Chemical and physical erosion in the South quadrangles, Virginia: Virginia Division of Mineral Mountain Anticlinorium, Maryland: Maryland Geological Resources Publication 35, 18 p. Survey Information Circular 19, 35 p. Henry, J., 1770, New and accurate map of Virginia: London, Granger, D.E., Kirchner, J.W., and Finkel, R.C., 1997, Quaternary Copperplate engraving with hand-color. downcutting rate of the New River, Virginia, measured from Herman, J.S., and Hubbard, D.A., 1990, A comparative study of differential decay of cosmogenic 26Al and 10Be in cave- travertine-marl-depositing streams in Virginia, in Herman, deposited alluvium: Geology, v. 25, p. 107–110. J.S. and Hubbard, D.A., eds., Travertine-marl: Stream Grant, J.A., Brooks, M.J., and Taylor, B.E., 1998, New constraints deposits in Virginia: Virginia Division of Mineral Resources on the evolution of Carolina Bays from ground-penetrating Publication 101, Charlottesville, Virginia, p. 43-64. radar: Geomorphology, v. 22, p. 325-345. Herodotus, 2005, An account of Egypt: Nuvision Publications, Gremos, A.A.,1992, Evaluation of late Mesozoic and Cenozoic 76 p. tectonism Atlantic Inner Coastal Plain margin near Hoffer-French, K.J., and Herman, J.S., 1989, Evaluation of

Richmond, Virginia. [M.S. thesis], Norfolk, Old Dominion hydrological and biological influences on CO2 fluxes from University, 138 p. a karst stream: Journal of Hydrology, v. 108, p.189-212. Hack, J.T., 1960, Interpretation of erosional topography in Hubbard, D.A., Jr., 1983, Selected karst features of the northern humid temperate regions: American Journal of Science, v. Valley and Ridge Province, Virginia: Virginia Division of 258-A, p. 80–97. Mineral Resources, Publication 44, one sheet. Hack, J.T., 1965, Geomorphology of the Shenandoah Valley, Hubbard, D.A., Jr., 1988, Selected karst features of the central Virginia and West Virginia: U.S. Geological Survey Valley and Ridge Province, Virginia: Virginia Division of Professional Paper 484, 83 p. Mineral Resources Publication 83, 1:250,000 map. Hack, J.T., 1973, Drainage adjustment in the Appalachians, in Hyland, S.E., 2005, Analysis of sinkhole susceptibility and Morisawa, M., ed., Fluvial geomorphology: Binghamton, karst distribution in the northern Shenandoah Valley, State University of New York, p. 51-69. Virginia: Implications for low impact development (LID) Hack, J.T., 1980, Rock control and tectonism: their importance site suitability models, [M.S. thesis], Blacksburg, Virginia in shaping the Appalachian highlands: U.S. Geological Tech, 56 p. Survey Professional Paper 1126 -B, p. 1-17. Ivester, A.H., Brooks, M.J., and Taylor, B.E., 2007, Sedimentology Hack, J.T., 1982, Physiographic divisions and differential uplift and ages of Carolina Bay sand rims: Geological Society of in the Piedmont and Blue Ridge: U.S. Geological Survey America, Abstracts with Programs, v. 39, no. 2, p. 5. Professional Paper 1265, 49 p. Ivester, A.H., Godfrey-Smith, D.I., Brooks, M.J., and Taylor, Hack, J.T., and Young, R.S., 1959, Intrenched meanders of B., 2003, Concentric sand rims document the evolution of a the North Fork of the Shenandoah River, Virginia: U.S. Carolina Bay in the middle Coastal Plain of South Carolina: Geological Survey Professional Paper 354-A, 10 p. Geological Society of America, Abstracts with Programs, v.

184 Chapter 11: Landscape Evolution in Virginia

35, no. 6, p. 169. Society of America, Reviews in Engineering Geology, v. 7, Ivester, A.H., Godfrey-Smith, D.I., Brooks, M.J., and Taylor, B., p. 139-155. 2004, The timing of Carolina Bay and inland dune activity Kochel, R.C., 1990, Humid fans of the Appalachian Mountains, on the Atlantic Coastal Plain of Georgia and South Carolina: in Rachochi, A.H., and Church, M., eds., Alluvial fans: A Geological Society of America, Abstracts with Programs, v. field approach: John Wiley and Sons, Chichester, p. 109- 36, no.5, p. 69. 129. Ivester, A.H., Leigh, D.S., and Godfrey-Smith, D.I., 2001, Langland, M., and Cronin, T., eds., 2003, Summary report of Chronology of inland eolian dunes on the Coastal Plain of sediment processes in Chesapeake Bay and watershed: U.S. Georgia, USA: Quaternary Research, v. 55, p. 293-302. Geological Survey, Water Resources Investigations Report Jacobson, R.B., and Coleman, D.J., 1986, Stratigraphy and recent 03-4123, 122 p. evolution of Maryland Piedmont flood plains: American Leigh, D.S., 2008, Late Quaternary climates and river Journal of Science, v. 286, p. 617-637. channels of the Atlantic Coastal Plain, southeastern USA: Jacobson, R.B., Miller, A.J., and Smith, J.A., 1989, The role Geomorphology, v. 101, p. 90-108. of catastrophic geomorphic events in central Appalachian Leigh, D.S., 2010, Latest Holocene channel and floodplain landscape evolution: Geomorphology, v. 2, p. 257-284. evolution for small streams in the southern Blue Ridge Jacobson, R.L., and Newell, W.L., 1982, Joint control of valley Mountains: Geological Society of America Abstracts with form and process in unconsolidated Coastal Plain sediments, Programs, v. 42, no. 1, p. 80. Westmoreland County, Virginia: Geological Society of Leigh, D.S., Pradeep S., and Brook, G.A., 2004, Late Pleistocene America, Abstracts with Programs, v. 14, no.1/2, p. 28. braided rivers of the Atlantic Coastal Plain, USA: Quaternary James, L.A., Rathburn, S.L., and Whittecar, G.R., 2009, Science Reviews, v. 23, p. 65–84. Introduction: Managing rivers with broad historical changes Litwin, R.J., Morgan, B., Eaton, L.S., Wieczorek, G., 2004, and human impacts, in James, L.A., Rathburn, S.L., and Assessment of Late Pleistocene to Recent climate-induced Whittecar, G.R., eds., Management and restoration of fluvial vegetation changes in and near Shenandoah National Park systems with broad historical changes and human impacts: (Blue Ridge Province, Va.): U. S. Geological Survey Open- Geological Society of America Special Paper 451, Boulder, File Report 2004–1351, 73 p. CO, p. v-x. Lowery, D. L., and J. F. Custer, 1990, Crane Point: An Early Johnson, G.H., 2008, Geology of the lower James-York Archaic site in Maryland: Journal of Middle Atlantic peninsula and Jamestown Island, in Bailey, C.W, and Archaeology, v. 6, p. 75-120. Lamoreaux, M.H. (eds.), Geology of Jamestown and the Mallison, D., Burdette, K., Mahan, S., and Brook, G., 2008, lower James River basin: 37th Annual Virginia Geological Optically stimulated luminescence age controls on late Field Conference guidebook, p. 1-10. Pleistocene and Holocene coastal lithosomes, North Johnson, G.H., Goodwin, B.K., Ward, L.W., and Ramsey, K.W., Carolina, USA: Quaternary Research, v. 69, p. 97-109. 1987, Tertiary and Quaternary stratigraphy across the Fall Markewich, H.W., Litwin, R.J., Pavich, M.J., and Brook, G.A., Zone and western Coastal Plain, southern Virginia, in 2009, Late Pleistocene eolian features in southeastern Whittecar, G.R., ed., Geological excursions in Virginia and Maryland and Chesapeake Bay region indicate strong North Carolina, guidebook to Southeast Section, Geological WNW–NW winds accompanied growth of the Laurentide Society of America 1987 Field Trips, Norfolk, Virginia. p. Ice Sheet: Quaternary Research, v. 71, p. 409-425. 87-144. Markewich, H.W., and Markewich, W., 1994, An overview of Johnson, G.H., Kruse, S.E., Vaughn, A.W., Lucey, J.K., Hobbs, Pleistocene and Holocene inland dunes in Georgia and the C.H., III, and Powars, D.S., 1998, Postimpact deformation Carolinas—morphology, distribution, age, and paleoclimate: associated with the late Eocene Chesapeake Bay impact U.S. Geological Survey Bulletin 2069, 32 p. structure in southeastern Virginia: Geology, v. 6, p. 507- Markewich, H.W., Pavich, M.J., and Litwin, R.J., 2010, Eolian- 510. deposit age, paleowind, and pollen data as evidence for Jones, J.A.A., 1971, Soil piping and stream channel initiation: periods of aridity and strong winds in the U.S. mid-Atlantic Water Resources Research, v.7, p.602-610. and southeastern Coastal Plain during rapid growth of the Keen, C.E., and Beaumont, C., 1990, Geodynamics of rifted Late Quaternary Laurentide ice sheet: Geological Society continental margins, in Keen, M.J., and Williams, G.L., of America, Abstracts with Programs, v. 42, no. 1, p. 150. eds., Geology of the continental margins of eastern Canada. Marple, R.T., and Talwani, P., 2000, Evidence for a buried fault The Geology of North America, I-1: Geological Society of system in the Coastal Plain of the Carolinas and Virginia America, Boulder Colorado, p. 19-55. - Implications for neotectonics in the southeastern United King, P.B., 1950, Geology of the Elkton area, Virginia: U.S. States: Geological Society of America Bulletin, v. 112, p. Geological Survey Professional Paper 230, 82 p. 200-220. Knapp, A.B., 1997, The Archeology of late Bronze Age Marsh, G.P., 1864, The earth as modified by human action: Cypriot society: The study of settlement, survey and Man and nature: New York, Scribners, (originally 581 landscape: University of Glasgow, Department of p.) reprinted 1965, Harvard University Press. Archaeology, 108 p. Martinson, D., Pisian, N.G., Hays, J.D., Imbrie, J., Moore, Kochel, R.C., 1987, Holocene debris flows in central Virginia, T.C., Jr., Shackelton, N.J., 1987, Age dating and the orbital in Costa, J.E., and Wieczorek, G.F., eds., Debris flows/ theory of the Ice Ages: Development of a high-resolution avalanches: Process, recognition, and mitigation: Geological 0–300,000 year chronostratigraphy: Quaternary Research,

185 The Geology of Virginia

v. 27, p. 1–29. Structures documenting Cretaceous and Tertiary deformation Matmon, A., Bierman, P.R., Larsen, J., Southworth, S., Pavich, along the Fall Line in northeastern Virginia: Geology, v. 5, M., and Caffee, M., 2003, Temporally and spatially uniform p. 437-440 rates of erosion in the southern Appalachian Great Smoky Mixon, R.B., Pavlides, L., Powars, D.S., Froelich, A.J., Weems, Mountains: Geology, v. 31, p. 155–158. R.E., Schindler, J.S., Newell, W.L., Edwards, L.E., and McAvoy, J.M., and McAvoy, L.D., 1997, Archaeological Ward, L.W., 2000, Geologic Map of the Fredericksburg 30’ investigations of Site 44SX202, Cactus Hill, Sussex County, X 60’ Quadrangle, Virginia and Maryland: U.S. Geological Virginia: Virginia Department of Historic Resources Survey, Geologic Investigations Series Map I-2607. Research Report Series No. 8, Richmond, Virginia, 192 p. Montgomery, D.R, 2007, Dirt: The erosion of civilizations: McDonald, J.N., and Bartlett, C.S., Jr., 1983, An associated musk University of California Press Berkeley, 296 p. ox skeleton from Saltville, Virginia: Journal of Vertebrate Montgomery, D.R., and Buffington, J.R., 1998, Channel Paleontology, v. 2, p. 458–470. processes, classification, and response, in Naiman, R.J., and Michalek, D.D., 1968, Fan-like features and related periglacial Bilby, R.E., eds., River ecology and management: lessons phenomena of the southern Blue Ridge, [Ph.D. dissertation], from the Pacific coastal ecosystem: New York, Springer, p. Chapel Hill, University of North Carolina, ,198 p. 13-42. Miller, A.J., 1990, Flood hydrology and geomorphic effectiveness Naeser, N.D., 1979, Fission track dating and geologic annealing in the central Appalachians: Earth Surface Processes and of fission tracks, in Jager, E., and Hunziker, J.C., eds., Landforms, v. 15, p. 119-134. Lectures in isotope geology: New York, Springer-Verlag, p. Miller, J.R., and Kochel, R.C., 2010, Assessment of channel 154-169. dynamics, in-stream structures and post-project channel Naeser, C.W., Naeser, N.D., Newell, W.L., Southworth, C.S., adjustments in North Carolina and its implications to Weems, R.E., and Edwards, L.E., 2004b, Provenance effective stream restoration: Environmental Earth Science, studies in the Atlantic Coastal Plain--what fission-track ages v. 59, no. 8, p. 1681–1692. of detrital zircons can tell us about the source of sediments: Mills, H.H., 1981, Boulder deposits and the retreat of mountain Geological Society of America, Abstracts with Programs, v. slopes, or “gully gravure” revisited: Journal of Geology, v. 36, no. 2, p. 114. 89, p. 649–660. Naeser, N.D., Naeser, C.W., Southworth, C.S., Morgan, B.A., Mills, H.H., 1988, Surficial geology and geomorphology of and Schultz, A.P., 2004a, Paleozoic to Recent tectonic and the Mountain Lake area, Giles County, Virginia, including denudation history of rocks in the Blue Ridge province, sedimentological studies of colluvium and boulder streams: central and southern Appalachians--Evidence from fission- U.S. Geological Survey Professional Paper 1469, 93 p. track thermochronology: Geological Society of America, Mills, H.H., 2000a, Controls on form, processes, and Abstracts with Programs, v. 36, no. 2, p. 114. sedimentology of alluvial fans in the Central and Southern Naeser, N.D., Naeser, C.W., Newell, W.L., Southworth, C.S., Appalachians: Southeastern Geology, v. 39, p. 281–313. Weems, R.E., and Edwards, L.E., 2006, Provenance studies Mills, H.H., 2000b, Apparent increasing rates of stream incision in the Atlantic Coastal Plain – what fission-track studies of in the eastern United States during the late Cenozoic: detrital zircons can tell us about the erosional history of the Geology, v. 28, p. 955–957. Appalachians: Geological Society of America, Abstracts Mills, H.H., Brakenridge, G.R., Jacobson, R.B., Newell, with Programs, v. 38, no. 7, p. 503. W.L., Pavich, M.J., and Pomeroy, J.S., 1987, Appalachian Nelson, K.J., Nelson, F.E., and Walegur, M.T., 2007, Periglacial mountains and plateaus, in Geomorphic systems of North Appalachia: Paleoclimatic significance of blockfield America, Graf, W.L., ed., Centennial Special, Vol. 2: elevation gradients, eastern USA: Permafrost and Periglacial Geological Society of America, Boulder, Colorado. p. Processes, v. 18, p. 61-73. 5-50. Newell, W.L., 1970, Factors influencing the grain of the Mills, H.H., and Delcourt, P.A., 1991, Quaternary geology topography along Willoughby Arch in northeastern of the Appalachian Highlands and interior low plateaus, : Geografiska Annaler, v. 52, series A, no. 2, p. in Morrison, R.B., ed., Quaternary nonglacial geology: 103-112. Conterminous U.S., The Geology of North America, vol. Newell, W.L., 1984, Architecture of the Rappahannock estuary- K-2: Geological Society of America, Boulder, Colorado, p. -neotectonics in Virginia, in Morisawa, M., and Hack, J.T., 611–628. eds., Tectonic geomorphology: London, Allen and Unwin, Mills, H.H., and Wagner, J.R., 1985, Long-term change in p. 321-342. regime of the New River indicated by vertical extent and Newell, W.L., and Rader, E.K., 1982, Tectonic control of weathering intensity of alluvium: Journal of Geology, v. 93, cyclic sedimentation in the Chesapeake Group of Virginia p. 131-142. and Maryland, in Lyttle, P. T., ed., Central Appalachian Mixon, R.B., Berquist, C.R., Jr., Newell, W.L., Johnson, G.H., geology, NE-SE GSA 1982 field trip guidebook: American Powars, D.S., Schindler, J.S., and Rader, E.K., 1989, Geological Institute, Falls Church, Virginia, p. 1-27. Geologic map and generalized cross sections of the Coastal Newell, W.L., and Wyckoff, J., 1992, Paleohydrology of four Plain and adjacent parts of the Piedmont, Virginia: U. S. watersheds in the New Jersey Coastal Plain: U.S. Geological Geological Survey Miscellaneous Investigation Series Map Survey Circular 1059, p. 23-28. I-2033, 2 sheets. Newell, W.L., and Queen, D.G., 2000, Hoverprobe 2000: A new Mixon, R.B., and Newell, W.L., 1977, Stafford fault system: tool for drilling in modern depositional environments: Drill

186 Chapter 11: Landscape Evolution in Virginia

Bits (Magazine of the National Drilling Association), v. 18, Park Nelson, K.J., Nelson, F.E., and Walegur, M.T., 2007, no. 2, p. 4-7. Periglacial Appalachia: Paleoclimate significance of Newell, W.L., and Clark, I., 2008, Geomorphic map of Worcester blockfield elevation gradients, eastern USA: Permafrost County, Maryland, interpreted from a LiDAR-based digital and Periglacial Processes, v. 18, p. 61-73. elevation model: U.S. Geological Survey Open-File Report Pavich, M.J., 1989, Regolith residence time and the concept 2008-1005, 34 p. of surface age of the Piedmont “peneplain”, in Gardner, Newell, W. L. & Dejong, B. D., 2011, Cold-climate slope T.W., and Sevon, W.D., eds., Appalachian geomorphology: deposits and landscape modifications of the Mid-Atlantic Geomorphology, v. 2, p. 181–196. Coastal Plain, Eastern USA: Geological Society, London, Pavich, M.J., and Obermeier, S.F., 1985, Saprolite formation Special Publications, v. 354(1), p. 259-276. beneath coastal plain sediments near Washington, D.C.: Newell, W.L., Pavich, M.J., Prowell, D.C., and Markewich, Geological Society of America Bulletin, v. 96, no. 7, p. H.W., 1980, Surficial deposits, weathering processes, and 886-900. evolution of an inner Coastal Plain landscape, Augusta, Pavich, M.J., Brown, L., Valette, S.J.N., Klein, J., and Middleton, Georgia, in Frey, R.W., ed., Excursions in southeastern R., 1985, 10Be analysis of a Quaternary weathering profile geology – Volume II. Field Trip Guide, Geological Society in the Virginia Piedmont: Geology, v. 13, p. 39–41. of America. American Geological Institute, p. 527-544. Pavich, M.J., Leo, G.W., Obermeier, S.F., Estabrook, J.R., 1989, Newell, W. L., Powars, D.S., Owens, J.P., Stanford, S.D., Investigations of the characteristics, origin and residence and Stone, B.D., 2000, Surficial geologic map of central time of the upland residual mantle of the Piedmont of Fairfax and southern New Jersey: U.S. Geological Survey, County, Virginia: U.S. Geological Survey Professional Miscellaneous Geologic Investigations Series, Map I 2540 Paper 1352, 58 pp. D, 3 sheets, Scale: 1:100.000. Pavich, M.J, Markewich, H.W., Litwin, R.J., Smoot, J., and Newell, W.L., Clark, I., and Bricker, O.P., 2004a, Distribution of Brook, G., 2010, Significance of marine oxygen isotope Holocene sediment in Chesapeake Bay as interpreted from stage OIS5a and OIS3 OSL dates from estuarine sediments submarine geomorphology of the submerged landforms, flanking Chesepeake Bay: Geological Society of America, selected core holes, bridge borings, and seismic profiles: U. Abstracts with Programs, v. 42, no. 1, p. 101. S. Geological Survey Open File Report 2004-1235 (version Pavlides, L., 1994, Continental margin deposits and the Mountain 1) Run fault zone of Virginia—stratigraphy and tectonics: U.S. Newell, W.L., Stone, B.D., and Harrison, R.W., 2004b, Holocene Geological Survey Bulletin 2076-B, 9 p. alluvium around Lefkosia (Nicosia) Cyprus: An archive of Pavlides, L., Bobyarchik, A.R., Newell, W.L., Pavich, M.J., land-use, tectonic processes, and climate change, in Martin- 1983, Late Cenozoic faulting along the Mountain Run fault Duque, J.F., et al., eds., Geo-Environment 2004, first zone, central Virginia Piedmont: Geological Society of international conference on monitoring, simulation, and America, Abstracts with Programs, v. 15, no. 2, p. 55. remediation of the geological environment, Segovia, Spain: Pazzaglia, F.J., and Brandon, M.T., 1996, Macrogeomorphic WIT Press, p. 71-80. evolution of the post-Triassic Appalachian mountains Newell, W.L., Stone, B., Harrison, R., Tsiolakis, E., Panayides, determined by deconvolution of the offshore basin I., Batihanli, H., Necdet, M., Berksoy, O., Zomeni, Z., and sedimentary record: Basin Research, v. 8, p. 255-278. Ozhur, A., 2004c, Chapter 2.4 (Geology) Surficial geology Pazzaglia, F.J., and Gardner, T.W., 1994, Late Cenozoic flexural of the Nicosia area, in DeCoster, M., et al., eds., Seismic deformation of the middle U.S. Atlantic passive margin: hazard and risk assessment of the greater Nicosia area: Journal of Geophysical Research, v. 99B6, p. 12,143- USAID, UNDP, UNOPS, Nicosia, Cyprus, p. 40-66. 12,157. Newell, W.L., Bricker, O.P., and Robertson, M.S., 2005, Geologic Pazzaglia, F.J., and Gardner, T.W., 2000, Late Cenozoic landscape map of the Colonial Beach, South 7.5’ Quadrangle, Virginia: evolution of the U.S. Atlantic passive margin: insights into U.S. Geological Survey Open File Report 2005-1025. a North American great escarpment, in Summerfeld, M.A., Nolde, J.E., and Giannini, W.F., 1997, Ancient warm spring ed., Geomorphology and global tectonics: New York, John deposits in Bath and Rockingham Counties, Virginia: Wiley and Sons, p. 282-302. Virginia Minerals, v. 43, p. 9-16. Peterson, C.A., and Whittecar, G.R., 2007, Geologic controls on Ollier, C.D., 1985, Morpholotectonics of continental margins cave development, Highland County, Virginia: Geological with great escarpments, in Morisawa, M., and Hack, J.T., Society of America, Abstracts with Programs, v. 38, no. 7, eds., Tectonic geomorphology: London, Allen and Unwin, p.138. p. 3-25. Pewe, T.L., 1983, The periglacial environment in North America, Overstreet, W.C., White, A.M., Whitlow, J.W., Theobald, P.K., in Porter, S.C., ed., Late Quaternary environment of the Jr., Caldwell, D.W., Cuppels, N.P., 1968, Fluvial monazite United States: Minneapolis, University of Minnesota Press, deposits in the southeastern United States: U.S. Geological p. 157–189. Survey Professional Paper 568, 85 p. Poag, C.W., 1992, U.S. middle Atlantic continental rise: Parham, P.R., Riggs, S.R., Culver, S.J., Mallinson, D., Burdette, Provenance, dispersal, and deposition of Jurassic to K., and Rink, W.J., 2010, Luminescence ages for Suffolk Quaternary sediments, in Poag, C.W., and Graciansky, P.C., shoreline in northeastern North Carolina: Geological eds., Geologic evolution of Atlantic continental rises: New Society of America, Abstracts with Programs, v. 42, no. 1, York, Van Nostrand Reinhold, 400 p. p. 101. Poag, C.W., 1999, Chesapeake invader: discovering America’s

187 The Geology of Virginia

giant meteorite crater: Princeton, N.J.: Princeton University Scott, T.W., 2006, Correlating late Pleistocene deposits on the Press, 183 p. coastal plain of Virginia with the glacial-eustatic sea-level Poag, C.W., and Sevon, W.D., 1989, A record of Appalachian curve [M.S. thesis], Norfolk, Old Dominion University, 112 denudation in postrift Mesozoic and Cenozoic sedimentary p. deposits of the U.S. middle Atlantic continental margin: Scott, T.W., Swift, D.J.P., Whittecar, G.R., and Brook, G.A., 2010, Geomorphology, v. 2, p. 119–157. Glacioisostatic influences on Virginia’s late Pleistocene Potter, N., and Moss, J.H., 1968, Origin of the Blue Rocks block coastal plain deposits: Geomorphology, v. 116, p. 175-188. field and adjacent deposits, Berks County, Pennsylvania: Schoeneberger, P., and Amoozegar, A., 1990, Directional Geological Society of America Bulletin, v. 79, p. 255-262. saturated hydraulic conductivity and macropore morphology Powars, D.S., 2000, The effects of the Chesapeake Bay Impact of a soil-saprolite sequence: Geoderma, v. 46, p. 31-49. Crater on the geologic framework and the correlation of Schultz, A.P., and Southworth, C.S., 1989, Large bedrock hydrogeologic units in southeastern Virginia, south of the landslides of the Appalachian Valley and Ridge province of James River: U.S. Geological Survey Professional Paper eastern North America, in Schultz, A.P., and Jibson, R.W., 1622, 53 p. eds., Geological Society of America Special Paper 236, p. Prince, P.A., and Henika, W.S., 2010a, Extinct rivers of the Blue 57-75. Ridge upland: a new perspective on erosional processes in Sherwood, W.C., Hartshorn, A., and Eaton, L.S., 2010, Soils, the southern Appalachians: Geological Society of America geomorphology, landscape evolution, and land use in Abstracts with Programs, v. 42, no. 1, p. 73. the Virginia Piedmont and Blue Ridge, in Fleeger, G.M., Prince, P.A., and Henika, W.S., 2010b, New physical evidence and Whitmeyer, S.J., eds., The Mid-Atlantic shore to the for stream capture as the driver of active retreat of the Appalachian Highlands: Field trip guidebook for the 2010 Blue Ridge escarpment: Geological Society of America, joint meeting of the Northeastern and Southeastern GSA Abstracts with Programs, v. 42, no. 1, p. 80. Sections: Geological Society of America Field Guide 16, p. Prowell, D.C., 1988, Cretaceous and Cenozoic tectonism on the 31-50, doi: 10.1130/2010.0016(02) Atlantic coastal margin, in Sheridan, R.E., and Grow, J.A., Smoot, J.P., 2004a, Sedimentary fabrics of stratified slope eds., The geology of North America, the Atlantic continental deposits at a site near Hoover’s camp, Shenandoah National margin, U.S. Decade of North American Geology Series, v. Park, Virginia: U.S. Geological Survey Open-File Report I-2: Boulder, Colorado, Geological Society of America, p. 2004–1059, 52 p. 557-564. Smoot, J.P., 2004b, Sedimentary characteristics of Late Rader, E.K., and Evans, N.H., eds., 1993, Geologic map of Pleistocene periglacial stratified-slope deposits in the Blue Virginia-expanded explanation: Virginia Division of Ridge of central Virginia: Geological Society of America, Mineral Resources, Charlottesville, 80 p. Abstracts with Programs, Northeast-Southeast Section Rathburn, S.L., Merritt, D.M., Wohl, E.E., Sanderson, J., and Meeting, v. 36, p. 95. Knight, H.A., 2009, Characterizing environmental flows Spotila, J.A., Bank, G.C., Reiners, P.W., Naeser, C.W., Naeser, for maintenance of river ecosystems: North Fork Cache la N.D., and Henika, W.S., 2004, Origin of the Blue Ridge Poudre River, Colorado, in James, L.A., Rathburn, S.L., escarpment along the passive margin of eastern North and Whittecar, G.R., eds., Management and restoration of America: Basin Research, v. 16, p. 41–63, doi: 10.1046/ fluvial systems with broad historical changes and human j.1365-2117.2003.00219. impacts: Boulder, Colorado, Geological Society of America Stolt, M.H., Baker, J.C., and Simpson, T.W., 1994, Soil- Special Paper 451, p. 143-157. saprolite-landscape relationships in the Piedmont and Blue Reusser, L.J., Bierman, P.R., Pavich, M.J., Zen, E., Larsen, J., Ridge highlands regions of Virginia: Virginia Agricultural and Finkel, R., 2004, Rapid late Pleistocene incision of Experiment Station Bulletin 94-1, 161 p. Atlantic passive-margin river gorges: Science, v. 305, p. Stose, G.W., and Stose, A.J., 1951, Blue Ridge Front - a fault 499–502. scarp: Geological Society of America Bulletin, v. 62, p. Richmond, G.M., and Fullerton, D.S., 1986, Quaternary 1371-1374. glaciations in the United States of America, in Sibrava,V., Trimble, S.W., 1974, Man-induced soil erosion on the southern Bowen, D.Q., and Richmond, G.M. eds, Quaternary Piedmont, 1700-1970. Washington, DC: Soil Conservation glaciations in the Northern Hemisphere: Oxford. Society of America, 180 p. Permagmon, p. 3–200. Tso, J. L., and Surber, J.D., 2006, Eocene igneous rocks near Riggs, S.R., and Ames, D.V., 2008, Geologic evolution of the Monterey, Virginia: A field study: Virginia Minerals, v. 49, lower Roanoke River drainage system in response to glacial p. 9-24. and post-glacial climatic and sea-level changes: Geological Vepraskas, M.J., Jongmans, A.G., Hoover, M.T., and Bouma, J., Society of America, Abstracts with Programs, v. 40, no. 4, 1991, Hydraulic conductivity of saprolite as determined by p. 27. channels and porous groundmass: Soil Science Society of Rosgen, D.L., 1996, Applied fluvial geomorphology: Pagosa America Journal, v. 55, p. 932-938. Springs, Colorado, Wildland Hydrology, 313 p. Wah, J.S., 2003, The origin and pedogenic history of Quaternary Sas, R.J., Jr., and Eaton, L.S., 2008, Quartizite terrains, geologic silts on the Delmarva Peninsula in Maryland, [Ph.D. controls, and basin denudation by debris flows: Their role in dissertation], University of Maryland, 260 p. long-term landscape evolution in the central Appalachians: Walker, H.J., and Coleman, J.M., 1987, Atlantic and Gulf Landslides, v. 5, no. 1, p. 97-106. Coastal Province, in Graf, W.L., ed., Geomorphic systems of

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North America, Geological Society of America, Centennial 32, no. 7, p. A-24. Special Volume 2, p. 51-110. Whittecar, G.R., and Duffy, D.F., 2000, Geomorphology and Walter, R.C., and Merritts, D.J., 2008, Natural streams and the stratigraphy of late Cenozoic alluvial fans, Augusta County, legacy of water-powered mills: Science, v. 319, no. 5861, Virginia, U.S.A.: Southeastern Geology, v. 39, p. 259–279. p. 299-304. Whittecar, G. R., Wynn, T.C., and Bartlett, C.S., Jr., 2007, Wampler, J.M., and Dooley, R.E., 1975, Potassium-argon Paleoenvironmental analysis of a middle Wisconsinan biota determination of Triassic and Eocene igneous activity site, southwestern Virginia, U.S.A.: Quaternary Research, in Rockingham County, Virginia: Geological Society of v. 68, p. 133-140. America, Abstracts with Programs, v. 7, no. 4, p. 547. Whitten, J., and Hancock, G., 2010, Using summit erosion rates Ward, D.J., Spotila, J.A., Hancock, G.S., and Galbraith, J.M., measured with 10Be to assess landscape disequilibrium 2005, New constraints on the late Cenozoic incision history in the Blue Ridge, Shenandoah National Park, Virginia: of the New River, Virginia: Geomorphology, v. 72, p. 54– Geological Society of America Abstracts with Programs, v. 72, doi: 10.1016/j.geomorph.2005.05.002. 42, no. 1, p. 79. Weems, R.E., and Edwards, L.E., 2007, Post-middle Miocene Wieczorek, G.F., Morgan, B.A., and Campbell, R.H., 2000, origin of modern landforms in the eastern Piedmont of Debris-flow hazards in the Blue Ridge of central Virginia: Virginia: Stratigraphy, v. 4, p. 35-48. Environmental and Engineering Geoscience, v. 6, p. 3-23. Wehmiller, J.F., Simmons, K.R., Cheng, H., Edwards, R.L., Wilkes G.P., Giannini, W.F, and Grimm, P.T., 1994, Notes on Martin-McNaughton, J., York, L.L., Krantz, D.E., and Sehn, ancient logs, Allegheny County, Virginia: Virginia Minerals, C.C., 2004, Uranium-series coral ages from the US Atlantic v. 40, p. 29–30. coastal plain – the “80 ka problem” revisited. Quaternary Williams, G.P., and Guy, H.P., 1973, Erosional and depositional International, v. 120, p. 3-14. aspects of Hurricane Camille in Virginia, 1969: U.S. Wheeler, R.L., 2006, Quaternary tectonic faulting in the eastern Geological Survey Professional Paper 804, 80 p. United States: Engineering Geology, v. 82, p. 165-186. Wolman, M.G., 1967, A cycle of sedimentation and erosion in White, W.A., 1950, Blue Ridge Front - a fault scarp: Geological urban river channels: Geografiska Annaler, v. 49A, p. 385- Society of America Bulletin, v. 61, p. 1309-1346. 395. Whittecar, G.R., 1985, Stratigraphy and soil development in Wolman, M.G., 1987, Sediment movement and knickpoint upland alluvium and colluvium, north-central Virginia behavior in a small Piedmont drainage basin: Geografiska Piedmont: Southeastern Geology, v. 26, p. 117–129. Annaler, Series A., Physical Geography, v. 69, p. 5-14. Whittecar, G. R., 1988, Alluvium and colluvium in terraces and Wright, E., 2007, Geologic studies of Carolina Bays in debris‑filled hollows, western North Carolina Piedmont: northeastern South Carolina: Geological Society of America, Geological Society of America, Abstracts with Programs, Abstracts with Programs, v. 39, no. 2, p. 5. v. 20, p. 139. Youngblood, M.A., 1998, The geomorphological history of an Whittecar, G.R., and Ryter, D.W., 1992, Boulder streams, debris alluvial fan complex in Nelson County, Virginia, [M.S. fans and Pleistocene climate change in the Blue Ridge thesis], Norfolk, Old Dominion University, 90 p. Mountains of central Virginia: Journal of Geology, v. 100, Zamkotowicz, M.D., 1997, Elevation as a control of boulder p. 487–494. stream formation in the Blue Ridge Province of Virginia. Whittecar, G.R., Pontier, N.K., Corrigan, P.B., Herman, S.W., [M.S. thesis], Norfolk, Old Dominion University, 78 p. Henderson, P.N., Gravette, J.V., and Luchetti, P.A., 1994, Zanner, C.W., Wysocki, D.A., Szuch, R.P., Vepraskas, M.J., and Soils and sediments in high-level Tertiary alluvium, White, J.G., 2003, Landscape evolution of a Carolina Bay: Gholsonville, Virginia: Virginia Journal of Science, v. 24, Geological Society of America, Abstracts with Programs, v. no. 2, p. 88. 35, no. 6, p. 77. Whittecar, G.R., Shamonsky, K.A., Magonigal, P.J., and Zeitler, P.K., Herczeg, A.L., McDougall, I., and Honda, M., 1987, Darke, A., 2000, Geomorphic evolution of fresh-water U-Th-He dating of apatite: A potential thermochronometer: tidal wetlands, Mattaponi River, Coastal Plain of Virginia: Geochim Cosmochin. Acta, v. 51, p. 2865-2868. Geological Society of America, Abstracts with Programs, v.

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