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Home , Esker, Glacial striation, Glaciofluvial deposits, Lane River, Wisconsin Glaciation

Surficial Geology of the Bradford, NH 7.5-minute Quadrangle

Gregory A. Barker and Joshua A. Keeley Geological Survey

Surficial geology mapped during the 2017-2018 field season

Geologic History

New Hampshire has been subject to multiple ice ages, but only evidence of the most recent one, the Glaciation and the Laurentide , is well preserved in the glacial and that were left behind as the ice melted. The Laurentide generally advanced into the area from the northwest to the southeast. The ice was at least 2000 meters thick through much of the region, covering even the highest summits (Bierman et al. 2015), and the weight of the ice and its slow but constant motion led to significant erosion of the pre-glacial landscape. Stoss and lee topography is common in many glaciated landscapes, where the leading, up-ice (stoss) side of a hill has a gentler slope while the down-ice side (lee) is much steeper resulting from or erosion by the ice. Photograph 1 shows a bedrock striation or a gouge across the bedrock surface, an indicator that the ice sheet passed over this area of New Hampshire.

Beginning around 14,500 years ago, the area began to become ice free as the glacier both retreated and thinned (Hodgson and Licciardi 2016) exposing the summit of nearby Mt. Cardigan to solar radiation. The high summit of Mount Kearsarge likely caused ice to stagnate and downwaste against its northwestern edge. In this scenario, ice front positions were controlled by pre-existing bedrock controls and not by climatic conditions (Caldwell 1978). Within the mapping area, meltwater initially flowed south through the area and east through the channel. Ice contact deposits, including an and , positioned against the southwest side of the leading to Lake Massasecum, indicate that meltwater exited the quadrangle here. The depth of Lake Massasecum suggests that an ice block occupied the basin to prohibit the meltwater and sediments from entering the basin. Rather the meltwater and were deposited against the ice or along the ice block’s western edge. The lack of deposits at the center of the area between the Warner River and Lake Massaseum suggest that ice occupied the area and directed meltwater toward Lake Massasecum. See Photos 2 and 3 for examples of sediment found along this deposit. Photograph 4 shows a typical glacial deposit, adjacent this kame deposit.

Ice eventually pulled back fully exposing the Warner River channel and it became the main meltwater outlet for the southern half of the quadrangle. Comparison of elevated terraced sediments within the Warner to a constriction point just east of Bradford center, indicate that these deposits likely graded to this constriction.

Two areas at the western edge of the Warner system, although ultimately drained to the Warner, are considered to be separate deposits. The first is in the area of the West Warner River. This area contains several terraces, designated Qst, that extend off quadrangle. Comparison of these terrace elevations with a constriction just east indicates this system likely graded to this constriction. The second area around the Newbury, NH town center and designated Qnv, predominantly consists of ice contact deposits in the form of a kame and several . Photographs 5 and 6 show exposed sediments of a kame just to the southwest of Newbury center. There is a small area of low outwash deposits just to the east of the town center. As the glacier melted back across the central hills of the quadrangle, till was predominantly deposited with a few areas of ice contact material accumulating along the south facing portion of these hills. Once the glacier reaches a nick point in the Lane River, at the eastern edge of south Sutton, NH, ice contact and begin to occur. These deposits have been collectively identified as the Middle Lane River Deposits (Qmlr). See Photograph 7 for a view looking north from the Lane River nick point.

As the glacier retreated further north, the upper reaches of the Lane River and Stevens Brook became exposed and provided valleys for meltwater to drain through. Sediments deposited along the lower two thirds of Stevens Brook are predominantly ice contact in origin, particularly at the immediate valley margin with alluvium occupying the center around the current stream position. The upper third of Stevens Brook has greater thickness and contains fully formed ice contact features such as eskers and . Photographs 8 and 9, respectively, show a large drop stone within the deposit and a small esker.

The Upper Lane River Deposit, in the vicinity of Kezar Lake and North Sutton, NH, was formed behind two meltwater channels. The easternmost channel is the current day outlet of the Lane, while the other channel, immediately west, was at a slightly higher elevation. A third channel exists to the west but is too high in elevation and so must have captured meltwater directly from the ice or subglacially. Behind the two outlets, sediments grade as an to the outlets. As the ice pulled back beyond Kezar Lake, an ice block appears to have remained within the lake. Evidence for this are location and depth of Kezar Lake, the abrupt termination of outwash plain against the lake margin and a and associated deposits along the southwestern edge of the lake. Photograph 10 shows this edge of Kezar Lake. It should also be noted that the topographic constriction to the south of Gile Pond, just southeast of Kezar Lake, was the location of an early higher elevation meltwater channel. The use of this meltwater channel was rapidly terminated, as there are no terraced deposits leading to the channel and sediments in the channel consist primarily of basal till.

References

Barker, G.A. and Olson, N.F., 2017, Surficial Geology of the New London 7.5 minute Quadrangle: New Hampshire Geological Survey, Map Geo-120-024000-SMOF, scale 1:24,000.

Bierman, P.R., Davis, P.T., Corbett, L.B., Lifton, N.A., Finkel, R.C., 2015, Cold-based Laurentide ice covered ’s highest summits during the , Geology v. 43, n. 12 pp. 1059- 1062.

Caldwell, D.H., 1978, Bedrock control of ice-marginal positions in central , Geology v. 6 pp. 278- 280

Goldthwait, and Stewart, unpublished data.

Harte, Philip T., Johnson, William, Geohydrology and Water Quality of Stratified-Drift Aquifers in the Basin, South-Central New Hampshire, USGS, Water-Resources Investigation Report 92-4154, 1995.

Hodgdon, Taylor, and Licciardi, Joseph, 2016, Developing a chronology for thinning of the in New Hampshire during the last , Northeast GSA annual meeting, Abstracts with Programs.

Koteff, Carl, 2012, Surficial Geologic map of the Warner Quadrangle, New Hampshire: New Hampshire Geological Survey, Map Geo-134-024000-SMOF, scale 1:24,000.

Quantum Spatial, 2016, LiDAR data for Watershed with FEMA HQ - Winnipesaukee AOI and WMNF AOI QL2 LiDAR, New Hampshire State Plane Data Set USGS Contract: G10PC00026 Task Order Number: G15PD00886 CT_River_Watershed_2015. Description of Map Units af – Artificial fill (Holocene)

Areas where surficial sediments may have been disturbed or removed and /or material transported from another location.

Qaf – Alluvial Fan (Holocene and )

Poorly sorted to boulder sized materials with some rounding, deposited in fan structures at the base of high sloping drainages. These fans may be the result of historic or periodic precipitation events that mobilized sediment down steep slopes. The resulting deposits can show some sorting but have limited amount of rounding to particles. These fans often overlie till at their upper, steeper sloped ends and valley bottom deposits, glaciofluvial or alluvium, at the distal end.

Qal - Alluvium (Holocene)

Sand to cobble, well rounded, poorly sorted deposits within the modern day floodplain.

Qic - Ice Contact (Pleistocene)

Glaciofluvial deposits laid down within or in close proximity to the ice margin. Deposits are generally poorly sorted, ranging from to moderately rounded cobbles with occasional boulders that may become increasingly stratified and may also grade to stratified deposits. Ice contact deposits can take the form of kames, eskers, ice channel fills and short braided stream plains.

Qls – Land Slide (Holocene and Pleistocene)

Deposit formed by a mass failure of sediment moved downslope. Originally deposited sediment is typically glacial till remobilized downslope to form a compact, poorly sorted diamicton. These deposits were found along the western edge of Mount Kearsarge within the quadrangle.

Qmlr – Middle Lane River Deposit (Pleistocene)

This deposit is located near the center of the quadrangle and largely consists of poorly sorted sand, gravel and cobble sediments up to 50 feet thick, although in most areas is less than 20 feet. A bedrock nick point for this area of the Lane River basin exists at the southeastern edge of this deposit. This nick point likely reduced the gradient of melt streams along this system providing the opportunity to build terraced fluvial sediments. However, most of the deposited sediments consist of ice contact deposits with eskers and kames being typical deposit morphologies.

Qnv – Newbury Village Deposit (Pleistocene)

This deposit is located around the center of Newbury, New Hampshire at the western terminus of the Warner River basin. The deposit predominantly consists of sand and gravel sediments with some cobbles and can be as much as 75 feet thick. There is one large kame within the deposit that exhibits stratified fluvial sediments that mostly dip to the north. There are also two eskers, immediately to the east of this kame, that also trend to the north. The remaining portion of this deposit, to the north, is dominated by eskers and outwash deposits that have a southerly trend. This juxtaposition leads the authors to conclude that there were differing meltwater inputs to form these subglacial and periglacial deposits. A meltwater input, likely from the southwest to form the kame and associated eskers and a second meltwater input from the north to deposit the remaining sediments.

Qsb – Stevens Brook Deposit (Holocene and Pleistocene)

This deposit consists of poorly sorted sands, gravels, cobbles and boulders, often not showing stratification. These sediments were predominantly deposited as ice contact materials subglacially and periglacially in meltwater. Deposit thicknesses are generally less than 35 feet, with the southern end of the deposit often less than 10 feet thick. This unit also contains undivided Holocene alluvium.

Qst – Stream terrace deposits (Holocene and Pleistocene)

Sand and gravel deposited as terraces, up to 20 feet above Holocene terrace levels. These deposits are located in a small basin at the southwest corner of the quadrangle around the West Branch of the Warner River. This deposit likely formed as the result of a constriction at the eastern end of this basin that ponded meltwater and sediments allowing these terraces to develop. Deposit thickness is highly variable, ranging from less than 10 feet to up to 65 feet on quandrangle.

Qt – Till (Pleistocene)

Poorly sorted mixture of silt, sand, gravel, and boulders that may be differentiated as basal or till based on mode of . Basal are generally less oxidized, light to dark gray in color, and more dense than ablation till as a result of being deposited under the mass of ice as the glacier advanced. Ablation tills are a diamict deposited from melting ice during deglaciation and are often sandier, less compact, and stained with iron oxides.

Qtt – Thin Till (Pleistocene)

Areas of exposed bedrock and till deposits interpreted to be less than 10 feet thick.

Qulr – Upper Lane River Deposit (Pleistocene)

Poorly sorted mixture of sand, gravels and cobbles up to 60 feet thick. These sediments were deposited into subglacial and periglacial environments by glacial meltwater. There is good evidence of an ice block within Kezar Lake and meltwater skirting the block along its southwestern edge and depositing sediments as a terrace and finally outleting onto an outwash plain south of Kezar Lake and the ice block. The outwash plain terminated at a bedrock nick point approximately 0.8 miles south of the ice block, near the current day position of the Lane River. This unit also contains undivided Holocene alluvium.

Qw – Wetland

Organic rich water laid sediments.

Qwv – Warner Village Deposit (Pliestocene)

Sand, gravel, silt and minor . As much as 40 ft (13m) thick. These deposits, near the eastern edge of quadrangle and along the Warner River valley, were deposited in part in standing water when ice still blocked the eastern part of the Warner River valley. Correlation with deposits in the eastern part of the Warner quadrangle is approximate. (Adopted from Koteff, C., 2012, NHGS Geo-134-024000-SMOF- Warner)

Qwwr – Western Warner River Deposit (Pleistocene)

Poorly sorted to stratified and well sorted sand, gravel, silt and minor clay. As much as 100 feet thick. These deposits are dominated by sediments transported and deposited by meltwater in subglacial and periglacial environments to form eskers, kames and small areas of outwash. Grading of stratified deposits, chiefly within kames, grade to a localized outlets that were not necessarily identified during this mapping. There are, however, several lower glaciofluvial deposits that seem to grade to a constriction point within the Warner River approximately a mile east of Bradford center, along Route 103. This relationship is based solely on terrace surface elevations, as there was very limited exposure of internal of these terraces or they had been mined out.

Photographs

Photo 1: Bradford DPW sand and gravel pit.

Photo 2: foreset beds in Bradford, NH

Photo 3: Picture of lower elevation rhythmically bedded lake deposits of a kame, Bradford, NH.

Photo 4: Typical glacial till deposit. Note the boulder at center contains striations on it’s surface indicating the till exposure is likely basal till, till beneath the ice directly in contact with bedrock.

Photo 5: Excavated face of a high level fine sand and silt bedded kame deposit.

Photo 6: Fluvial form within a lower section of the Newbury kame. This form is indicative of high velocity stream deposition.

Photo 7: Constriction point at the Middle Lane River deposit, looking north. Sediments to north- northwest within this section of the Lane grade to this location.

Photograph 8: Drop stone at the edge of the Stevens Brook Deposit.

Photograph 9: Small esker within the Stevens Brook Deposit.

Photograph 10: Coarse gravel at the edge of Kezar Lake, indicative of the edge of an outwash plain. View looks northward where an ice block occupied the lake. Till hill tops can be seen beyond.