277
Glacial Deposits
Drumlins, Eskers,
and Kames
Moraines are not the only landforms
deposited by glaciers. Some landscapes are
characterized by numerous elongate parallel hills made of till. Other areas exhibit
conical hills and relatively narrow winding
ridges composed largely of stratified drift.
DRUMLINS. Drumlins are streamlined, asymmetrical
hills composed of till (Figure 11.27). They range in
height from 15 to 60 meters (50 to 200 feet) and average 0.4 to 0.8 kilometer (0.25 to 0.50 mile) in length.
The steep side of the hill faces the direction from which
the ice advanced, whereas the gentler slope points in the
direction the ice moved. Drumlins are not found singly
but rather occur in clusters, called drumlin fields. One
such cluster, east of Rochester, New York, is estimated to
contain about 10,000 drumlins. Their streamlined shape
indicates that they were molded in the zone of flow
within an active glacier. It is thought that drumlins originate when glaciers advance over previously deposited
drift and reshape
the material.
ESKERS AND
KAMES. In some
areas that were
once occupied by
glaciers, sinuous ridges composed largely of sand
and gravel can be found. Known as eskers, these
ridges are deposited by meltwater rivers flowing
within, on top of, and beneath a mass of motionless,
stagnant glacial ice (Figure 11.27). Many sediment
sizes are carried by the torrents of meltwater in the
ice-banked channels, but only the coarser material
can settle out of the turbulent stream. In some areas
Retreating
glacier
Drumlin field
End moraine
Esker
Kame
Bedrock
Ground moraine
Outwash
plain
Kettle lake
FIGURE 11.27 This hypothetical area illustrates many common depositional landforms. The outermost end moraine
marks the limit of glacial advance and is called the terminal end moraine. End moraines that form as the ice front
occasionally becomes stationary during retreat are called recessional end moraines. (Drumlin photo courtesy of Ward’s
Natural Science Establishment; Kame, Esker, and Kettle photos by Richard P. Jacobs/JLM Visuals)
Ronkonkoma moraine
Long Island
Harbor Hill moraine
Nantucket
Martha’s
Vineyard
Boston
NJ
NY
Cape
Cod
RI
CT
MA
FIGURE 11.26 End moraines make up substantial parts of Long Island, Cape Cod,
Martha’s Vineyard, and Nantucket. Although portions are submerged, the Ronkonkoma
moraine extends through central Long Island, Martha’s Vineyard, and Nantucket. It was
deposited about 20,000 years ago. The Harbor Hill moraine, which formed about 14,000
years ago, extends along the north shore of Long Island, through southern Rhode Island
and Cape Cod.
D I D Y O U K N O W ?
Studies have shown that the
retreat of glaciers may reduce
the stability of faults and hasten
earthquake activity. When the
weight of the glacier is
removed, the ground rebounds.
In tectonically active areas
experiencing post-glacial
rebound, earthquakes may
occur sooner and/or be
stronger than if the ice were
present.
Glacial Deposits
Drumlins, Eskers,
and Kames
Moraines are not the only landforms
deposited by glaciers. Some landscapes are
characterized by numerous elongate parallel hills made of till. Other areas exhibit
conical hills and relatively narrow winding
ridges composed largely of stratified drift.
DRUMLINS. Drumlins are streamlined, asymmetrical
hills composed of till (Figure 11.27). They range in
height from 15 to 60 meters (50 to 200 feet) and average 0.4 to 0.8 kilometer (0.25 to 0.50 mile) in length.
The steep side of the hill faces the direction from which
the ice advanced, whereas the gentler slope points in the
direction the ice moved. Drumlins are not found singly
but rather occur in clusters, called drumlin fields. One
such cluster, east of Rochester, New York, is estimated to
contain about 10,000 drumlins. Their streamlined shape
indicates that they were molded in the zone of flow
within an active glacier. It is thought that drumlins originate when glaciers advance over previously deposited
drift and reshape
the material.
ESKERS AND
KAMES. In some
areas that were
once occupied by
glaciers, sinuous ridges composed largely of sand
and gravel can be found. Known as eskers, these
ridges are deposited by meltwater rivers flowing
within, on top of, and beneath a mass of motionless,
stagnant glacial ice (Figure 11.27). Many sediment
sizes are carried by the torrents of meltwater in the
ice-banked channels, but only the coarser material
can settle out of the turbulent stream. In some areas
Retreating
glacier
Drumlin field
End moraine
Esker
Kame
Bedrock
Ground moraine
Outwash
plain
Kettle lake
FIGURE 11.27 This hypothetical area illustrates many common depositional landforms. The outermost end moraine
marks the limit of glacial advance and is called the terminal end moraine. End moraines that form as the ice front
occasionally becomes stationary during retreat are called recessional end moraines. (Drumlin photo courtesy of Ward’s
Natural Science Establishment; Kame, Esker, and Kettle photos by Richard P. Jacobs/JLM Visuals)
Ronkonkoma moraine
Long Island
Harbor Hill moraine
Nantucket
Martha’s
Vineyard
Boston
NJ
NY
Cape
Cod
RI
CT
MA
FIGURE 11.26 End moraines make up substantial parts of Long Island, Cape Cod,
Martha’s Vineyard, and Nantucket. Although portions are submerged, the Ronkonkoma
moraine extends through central Long Island, Martha’s Vineyard, and Nantucket. It was
deposited about 20,000 years ago. The Harbor Hill moraine, which formed about 14,000
years ago, extends along the north shore of Long Island, through southern Rhode Island
and Cape Cod.
D I D Y O U K N O W ?
Studies have shown that the
retreat of glaciers may reduce
the stability of faults and hasten
earthquake activity. When the
weight of the glacier is
removed, the ground rebounds.
In tectonically active areas
experiencing post-glacial
rebound, earthquakes may
occur sooner and/or be
stronger than if the ice were
present.