Geologic Relationships of Slope Movement in Northern Alabama
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Geologic Relationships Of Slope Movement in Northern Alabama u.s. GEOLOGICAL OSURVEY BULLETIN 1649 0 •• ,,I • ;. II II !r- ,, ...~ =" .. .. .I II .. L.- =- r r .. .. n "l -= :- rvt;; ...,_fl' ., ,., "I ~ .., • .:. ..1:1 !l ~ 01111! .. ,)1 .. I Lo •"'' 1111 w ... il "'·· d • ~''':II ~ "I r .. .. Geologic Relationships Of Slope Movement in Northern Alabama By JOHN S. POMEROY and ROGER E. THOMAS U.S. GEOlOGICAl SURVEY BUllETIN 1649 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director UNITED STATES GOVERNMENT PRINTING OFFICE: 1985 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 Library of Congress Cataloging-in-Publication Data Pomeroy, johnS., 1929- Geologic relationships of slope movement in northern Alabama. (U.S. Geological Survey bulletin ; 1649 Bibliography: p. 13 Supt.ofDocs.no.: I 19.3:1649 1. Earth movements-Alabama. 2. Slopes (Physical geog raphy)-Aiabama. I. Thomas, Roger, E. II. Title. Ill. Series. QE75. 89 [QE598] 557.3 s [551.4'36] 84-600402 CONTENTS Abstract 1 Introduction 1 Cumberland Plateau 3 Sand Mountain 3 Jackson County Mountains 4 Warrior Basin 7 Highland Rim 10 East Gulf Coastal Plain 10 Summary 11 References 13 FIGURES 1. Map showing area investigated for slope-stability study and physiographic regions in northern Alabama 2 2. Photographs showing recent and older slope movements in northern Alabama 6-7 3. Maps showing recent and older slope movements and slide-prone terrain, northern Alabama 8-9 4. Map showing slope movement-prone areas in northern Alabama 12 TABLE 1. Stratigraphic units whose derivative soils are moderately to highly susceptible to movement 4-5 Contents Ill Geologic Relationships of Slope Movement in Northern Alabama By John S. Pomeroy and Roger E. Thomas Abstract Thomas, 1979, 1982) as part of a comprehensive in vestigation involving the Appalachian Plateau Prov Slope-stability problems in northern Alabama result ince. Adjoining areas of the Interior Low Plateaus from slope movement that takes place within all major and Coastal Plain Provinces to the north and west physiographic sections which include the Cumberland Plateau, Highland Rim, and Eastern Gulf Coastal Plain. were also examined. This area is bordered by Sand Slope movements, commonly debris slides, slumps, earth Mountain in the east and by longitude 88 ° in the flows, and complex forms, take place in the colluvium or west. The State boundary and latitude 34 ° border the at the contact between the colluvium and the underlying area in the north and south, respectively (fig. 1). weathered mudstone or shale in the Cumberland Plateau. Aerial photography at scales of 1:20,000 (1971, Slopes underlain by the Pennington Formation and for the 1972), 1:40,000 (1977-1979), and 1:80,000 (1977) upper part of the Bangor Limestone of Late Mississippian was used in the study. Photo interpretation was fol age are the most susceptible to movement. Toppling fail lowed by reconnaissance from vehicles and selected ures, involving the overlying subhorizontal sandstone foot traverses. Included in the inventory were identi caprock of the Pottsville Formation of Pennsylvanian age, fication of recently active and historic landslides, pre are largely controlled by separation along the vertical historic landslides, and the outlining of zones consid joint faces and by undermining caused by rapid weather ing of the underlying incompetent mudstones and shales ered by the investigator to be most susceptible to of Mississippian age. Old slope movements as long as 0.9 slope failure on the basis of landslide incidence, rock km have been documented near Huntsville. Road con and soil textures, and topography. Pomeroy was re struction in that area reactivated a small part of one old sponsible for the inventory west of longitude 86 o. slope movement. In the extreme western part of the Cum- Thomas investigated the Appalachian Plateau Prov berland Plateau, colluvium derived from shale and mud- ince east of longitude 86 ° (fig. 1). stone of the Parkwood Formation of Late Mississippian In this report, we have adopted the term slope and Early Pennsylvanian age is prone to sliding. Slopes underlain by the Pride Mountain Formation movement rather than landslide as a general, inclu of Late Mississippian age in the Highland Rim section sive term except for movements that involve only show evidence of present and past instability. Recent slid- sliding. Landslide has been widely used as an all ing has taken place in colluvium derived from mostly gray- inclusive term for almost all types of slope movement ish-green shale. Two large prehistoric bedrock slumps (0 . .5 including some that involve little or no sliding and 1.3 km wide) have displaced the overlying Hartselle (Varnes, 1978, p. 11). The popular geomorphic term, Sandstone in a northwest-trending, joint-controlled valley mass movement, is synonymous with slope movement southwest of Tuscumbia. and is not used in this report. Sand, gravel, and less abundant clay of the Tusca- Five types of slope movement (Varnes, 1978, loosa Group of Late Cretaceous age mantle the Eastern fig. 2.1) are present in northern Alabama. They in Gulf Coastal Plain in northern Alabama. Highway con- struction in this unit, near Hamilton, has caused major clude falls (rockfalls), topples, slides (earth slumps, slope movements whose failure surfaces can be traced to debris slides), flows (debris and earth flows, debris thin clay seams. avalanches), and complex movements (slump-earth flows, debris slide-earthflows). Rock falls are extremely rapid free falls of bed INTRODUCTION rock. Alternating competent and incompetent lithol ogies, in addition to closely spaced vertical joints A large part of northern Alabama was examined parallel to the major drainages, are contributing fac 1n 1979-1981 for slope stability (Pomeroy, 1982b; tors to the process. Topples are rock blocks that have Introduction N sao 35°;-p TENNESSEE C'1 ---------------------------------------------------------ALABAMA 1'1) 0 0 OQ ;::;· I JCM I ;iiC 1'1) [ o· /EGC :I -, -s·::r"" 0..1 "" s. Paint Rock 0 Vl ~I 0 C/)1 ~ ~ JCM "((.,~ ~ ' 0 < q,v?'- 1'1) ;1 EGCP 3 a1'1) Cl)l' :;- z ;/ ~ I :;:. I ~ :I > iii I C"' I ~\) Q.l I WB I 3 I ~\..~ I Q.l '!01(:. I \)0~ 0 Cullman I IHamilton / / 0 10 20 MILES WB I I SM / I I I / 0 10 20 KILOMETERS 34°~--------~--------------------------------------------------~--------' EXPLANATION A Locality discussed in text EGCP, East Gulf Coastal Plain SQV, Sequatchie Valley Boundary between physiographic sections JCM, Jackson County Mountains TV, Tennessee Valley Boundary between physiographic districts LIM, Little Mountain WB, Warrior Basin Physiographic unit boundaries MOV, Moulton Valley are slightly modified from Sapp and SM, Sand Mountain Emplaincourt, 1975 Figure 1. Map showing area investigated for slope-stability study and physiographic regions in northern Alabama. rotated forward. Slides are either earth slumps in The Cumberland Plateau section in divided in volving rotational movement with an upward curv to several physiographic districts (Sapp and Em ing rupture surface or are debris slides which take plaincourt, 197 5). The districts applicable to this dis place along planar or mildly undulatory surfaces and cussion are Sand Mountain, Jackson County are called translational movements. Both types of Mountains, and the Warrior Basin (fig. 1). slide movements can be very slow to rapid. Flows in northern Alabama are of three types, ranging in movement patterns from extremely rapid (debris av Sand Mountain alanche) to very rapid (debris flow) to rapid to very slow (earth flows). Flows in surficial materials show Sand Mountain is a submaturely dissected syn movement resembling that found in the flows of vis clinal plateau of moderate relief capped by the Potts cous fluids. ville Formation. The boundaries are distinct except A debris avalanche has a long and relatively at the southwest end where Sand Mountain subtly narrow track along a steep mountain or hill slope and merges with the Warrior Basin. The sandstone es is usually preceded by copious precipitation. A debris carpment along both sides of Sand Mountain ranges flow, similar to a debris avalanche, is commonly a in relief from 122 m (400 ft) at the south end to 305 wider and less viscous movement. An earthflow com m ( 1,000 ft) at the (north end). Slope movements are monly shows shear surfaces along the flanks and ba common only along the flanks of the plateau. sal surface even though the distribution of velocities That part of the east side of Sand Mountain within the displaced material may indicate plastic that was inventoried for slope movements is largely flow (Varnes, 1978, fig. 2.1). Indeed, most slope covered by colluvium within which small (<30 m movements are complex in that features of two or wide) debris slides, slumps, and complex forms are more basic slope movements are represented, as in found above and below roads. slump-earthflows, debris slide-earthflows, and so on. The west side of Sand Mountain has greater Complex movements involve an upper zone of deple relief than the east side. The slope is largely covered tion (slump, debris slide) and a lower zone of ac by colluvium and is generally slide-prone. All recent cumulation or deposition (flow). slope movements have been induced by man and are Rocks exposed in the area range from Ordovi largely slump-earthflows or debris slide-earthflows. cian to Cretaceous in age. The relatively simple struc For example, along Alabama 73 less than 1 km ture is made up of subhorizontal strata except for the southwest of the tri-State intersection (AL-TN-GA), Sequatchie Valley west of Sand Mountain (fig. 1). colluvial movements are restricted to the upper part The physiographic sections include the Cumberland of the slope underlain by the Pennington Formation Plateau (Appalachian Plateaus Province), Highland (fig. 1, locality A).