EAS 2200, Spring 2011
Lab 12: Fall Creek
Name _____________________
Tuesday
Wednesday
Field Trip I
FALL CREEK VALLEY IN THE CORNELL PLANTATIONS
Objectives:
a) Observe the effects of glaciation on the development of landscapes in the Ithaca area.
b) To understand the post-glacial evolution of the Fall Creek valley with emphasis on fluvial processes.
c) To reconstruct some of the topographic features that existed in the Fall Creek area prior to the last glacial
period.
d) To become familiar with the use of topographic maps in the field.
Note: Please read this exercise BEFORE the field trip. We will board vans in the Snee Hall parking lot and leave
sharply at 2:00PM. (Please be on time and dress accordingly for the weather).
Part A. Background
The landforms of the Ithaca and the surrounding Finger Lakes region are primarily the
result of two factors: the underlying bedrock and glacial processes. The bedrock throughout
central New York is Devonian in age (Devonian period: 355-410 million years ago) and is
composed mostly of siltstone and shale. These rocks are relatively undeformed (unlike the rocks
100 miles to the southeast in the Appalachian Mountains) and as a result are still nearly
horizontal.
The bedrock in this region has been affected by at least 3 periods of glaciation during the
Pleistocene epoch (2 million to 10,000 years ago). Information from deep-sea drill cores,
however, indicates that there have been as many as 20 such ice ages spaced roughly at 100,000year intervals during the 2 million years of the Pleistocene epoch. The last period of glaciation
began a little more than 100,000 years ago and ended about 10,000 years ago. This glacial
interval was called the Wisconsin glaciation (Fig. 1), within which there were several ice
advances (when the ice margin was south of Ithaca), separated by warmer interstadial periods
(when the ice front retreated to the north of Ithaca--see Fig. 2). During the last advance of the
Wisconsin glaciation (~18,000 years ago) the ice sheet reached its most southerly position and
extended as far south as Long Island, N.Y., Williamsport, Pa., and Cincinnati, Ohio (Figs. 1 and
2). It has been estimated that the thickness of the ice overlying the Ithaca area at that time was
approximately 1500-2000 meters. After the last advance the Wisconsin ice sheet (also called the
Laurentian) began to recede. By about 14,000 years ago, the ice margin had retreated to the
vicinity of Ithaca (Fig. 2B), depositing glacial drift as recessional moraines (such as the Valley
Head moraines south of Ithaca) during glacial stillstands, and ground moraines during periods of
more continuous glacial retreat (Fig. 3). During this last recessional period the glacial Lake
Ithaca was formed.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Figure 1. Approximate maximum extent of the major ice sheets in North America during the Wisconsin ice age. At
climax, sea level was as much as 300 feet lower than it is today. Shorelines during the Wisconsin ice age were
located approximately with dashed lines on the map.
Ice remained in the Cayuga trough (Cayuga valley) after the land at higher elevations on
either side of the trough (as well as the smaller valleys--e.g. Fall Creek) were free of ice (Fig. 6).
Because the Finger Lakes belong to the St. Lawrence drainage system and flow northward, the
ice "fingers" that occupied the N-S valleys during the waning stages of glaciation blocked the
flow of water into the St. Lawrence drainage by forming an ice dam across the Cayuga trough.
As a result, water ponded against the ice sheet and resulted in the formation of Lake Ithaca
(called a pro-glacial lake). Water of this pro-glacial lake overflowed southward across a divide,
into the Susquehanna drainage (Fig. 2B). The site of the southward overflow of the lake was
located approximately 2 miles south of Brooktondale at an elevation of 980 feet. As the ice
margin continued to recede, a lower overflow midway up Cayuga Lake was uncovered. This
allowed melt-water to flow west to Seneca Lake in the vicinity of Ovid (Fig. 4). This water in
turn drained out of the south end of Seneca Lake and flowed southward toward Horseheads. A
new pro-glacial lake, "Lake Newberry", was thus formed about at the 900 ft level. With further
glacial recession, outlets at lower elevations were opened near the north end of Cayuga Lake and
caused a succession of pro-glacial lakes to be lowered in steps.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Figure 2. Four stages of Wisconsin deglaciation in New York. (A) Dashed line shows the location of the maximum
advance of the ice. (B) The melt water is channeled down the Susquehanna River. (C) The Finger Lakes are nearly
formed. (D) The Finger Lakes are formed and nearly all lakes drain down the Mohawk River to the Hudson; the
Little Falls divide is eroded away. All lakes shown are termed "pro-glacial".
Deltas developed along the shorelines of these pro-glacial lakes at the mouths of streams
such as Fall Creek. The highest delta that we will see on this field trip is approximately at the
970 ft level and was formed just below the surface of Lake Ithaca when the lake level was at 980
feet and the outlet of the lake was to the south, into the Susquehanna drainage. Other deltas can
be seen on the campus (e.g. the Ag. quad, the Engineering quad, the Arts quad) and represent
sediment deposition in deltas of lakes at successively lower elevations (Fig. 5).
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Figure 3. Schematic diagram of a receding glacier and the geologic features left behind.
Figure 4. Spillover channels are cut across divides when a 'high-elevation' pro-glacial lake in one basin overtops a
divide and water drains across to a lower lake.
Figure 5. Deltas formed during short periods (approx. 100 years) when pro-glacial lakes maintained a constant
depth. These deltas formed at the valley mouth, and are left "hanging" as the lake level is lowered in steps 1-3. In
steps 2 and 3 the streams are entrenched into the earlier delta, and waterfalls form and recede upstream.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Figure 6. Physiographic diagram, Cayuga Lake Basin.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Many of the creeks that flowed into these pro-glacial lakes were able to erode down
toward their base level during brief periods of constant lake level, and developed meandering
patterns. As the local base level of Fall Creek was lowered, due to the successive lowering of the
pro-glacial lakes, the creek entrenched its valley and formed meandering stream channels at
successively lower levels. These meandering channels are preserved as "scars" throughout the
present day Fall Creek valley. The earliest such meander scar that we will see on this trip is in
the Newman Arboretum, at approximately the 900 foot level. These meander traces formed
during the "Lake Newberry" lake level when the pro-glacial lake was about at a 900 ft elevation.
The lower meander scars that we will see on this field trip are progressively younger. As the
level of pro-glacial Lake Ithaca fell during the deglaciation, the many valleys of the Ithaca area
drained and streams began dissecting former lake, stream, and glacial deposits.
Fall Creek presently flows west-southwest along a long linear valley (a lineament
observable from space) at the base of an escarpment (Mount Pleasant-Turkey Hill; Fig. 4). The
creek has preferentially eroded its left bank as it migrated laterally down the dip of gently tilted
Paleozoic rocks. Fall Creek may have flowed far to the southwest in pre-glacial times. It has
been speculated that prior to Pleistocene glaciation, Fall Creek had been captured by a northflowing river that was located where the present valley of Cayuga Lake is today. As the
Wisconsin ice sheets advanced southward across New York, N-S oriented valleys such as that of
the hypothetical north-flowing "Cayuga River" were strongly eroded by the glaciers. E-W
oriented tributaries such as the Fall Creek drainage, however, were overridden by the ice sheets
and not significantly altered by glacial erosion. Therefore a glacial trough was deeply eroded in
the Cayuga Valley, but the valleys of tributaries such as Fall Creek were filled with glacial debris
and left "hanging" above the Cayuga trough. The waterfalls and gorges of the campus are
therefore the result of stream erosion (down-cutting) of the E-W tributary streams following the
lowering of their base levels by glacial erosion of the Cayuga trough.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Summary of Glacial History
Years ago
<12,100
"Post-Lake Iroquois Lakes" with drainage to the north via Lake Ontario
and the St. Lawrence; post-glacial rebound to north causes tilting in Lake Cayuga of 5 feet/mile
and the development of the flood plain at the south end.
12,400-12,100
Glacial Lakes, Dawson (early: 700-480 feet) and Iroquois (late: 400-435
feet); drainage in Lake Iroquois via Rome to Mohawk Valley.
12,400-12,600
Glacial Lake Newbury elevation at 920-900 feet; beginning of eastward
drainage via Syracuse Channels and Mohawk Valley. Falling levels in glacial Lake Warren
(900-830 feet) with continued drainage through Syracuse Channels.
12,800-13,000
Pro-glacial Lakes Brookton, Danby, and Slaterville, and Early Lake
Ithaca; drainage to the south via White Church outlet at 980 ft. Regional drainage is to the
Susquehanna system. Lake Newberry drained west to Lake Watkins via Ovid; channel
elevation is at 900 feet.
14,000-13,000
Deposition of "Valley Heads" and "Tully" Moraines in Finger Lakes
region; approximate rate of receding glacier is 84 feet/year or 26 meters/year.
18,000
Southern limit of glaciation approximately Williamsport, PennsylvaniaLong Island, New York.
<100,000
Ithaca region covered by Wisconsin glaciation; ice tongues extended up
Fall Creek Valley and Cascadilla Valley from the thick through of ice that filled what is now
Cayuga Valley.
125,000?
Formation of interglacial gorges.
>140,000?
Illinoian glaciation.
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Part B. Field Trip Log:
1. Meet promptly at 2:00 p.m. at the Snee Hall parking lot. We will park at Plantations
Overlook Road, at the base of the white water tower. From this stop at the elevation of 970 ft
contour, the late-glacial and post-glacial evolution of Fall Creek valley can be studied. The
water tank is located on what was a fan-delta that was deposited by Fall Creek in pro-glacial
Lake Ithaca. When this delta was forming, the lake surface was at a 980 ft elevation. A soil pit
in the vicinity shows a well-sorted sandy loam that indicate re-working of the sediment by
running water. From this vantage point, broad, shallow channels can be seen to radiate down the
delta slope.
2. Walk down the hill into the Newman Arboretum. The Arboretum crosses the slopes of an
abandoned meander of Fall Creek with a floor at about 900 ft, the regional level of glacial "Lake
Newberry". Lake Newberry drained past the south end of Seneca Lake towards Elmira, and was
an ice-marginal lake across central New York. A smaller meander terrace 30 ft lower still shows
an abandoned meander channel at its outer bend. Study the two terraces forming the bowls and
smooth rounded slopes. These terraces were formed by former meanders of the creek at two
different times.
3. Walk down towards Fall Creek. Study the contact between Paleozoic bedrock (bedded
siltstone & shale of the Ithaca Formation) and the sediments along the bank of Fall Creek.
Notice the large slabs of bedrock in the creek; these slabs are transported during floods. A short
distance down stream from the dam, Fall Creek drops over a low waterfall into a segment a few
hundred meters long in which no bedrock is exposed. Locate your position and mark the contact
between the bedrock and the loose unconsolidated sediment on your map.
4. Walk down to the Forest Home Drive Bridge. Look both up and downstream and note the
contacts between bedrock and glacial sediments. Mark these positions on your map.
5. Walk down into the Wildflower Gardens. The garden has grown on the floor of Fall Creek
valley in a segment of a buried interglacial valley. A short distance down stream from the
parking area, Fall Creek drops over a low waterfall into a segment a few hundred meters long in
which no bedrock is exposed. Mark this contact on your map. Study the recently abandoned
meander (still part of the flood plain of the present day Fall Creek). Compare the freshness of
the floodplain and cut bank with the older features in Newman Arboretum. An oxbow swamp is
in a well-defined channel at the base of the cut bank of the meander scar.
6. Walk to the Plantations Road. It follows an abandoned meander known as the "Forest Home
Runaround". Note the poorly drained area at the base of the slope and the meander core that
forms the hill at the center. At what elevation is this meander? Where Plantation road and the
"runaround" intersect Forest home drive along Beebe Lake, no bedrock is exposed. Beebe Lake,
like several valley segments upstream, is a segment of an interglacial valley with a floor below
the modern channel of Fall Creek.
7. Walk to the creek entrance into Beebe Lake. Fall Creek flows through a narrow gorge before
entering Beebe Lake. What controls the course of the creek here? At the stone bridge over the
upper end of Beebe Lake and near the dam, the rock walls of a buried interglacial valley are
exposed. Beebe Lake covers glacial sediments. Note the difference between the glacial deposits
exposed at the lake edge and the bedrock along the creek. How would you identify glacial
deposits?
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EAS 2200, Spring 2011
Lab 12: Fall Creek
Part C. Questions
Prepare answers to the following questions, based on the notes you took during the field trip and
the attached notes. Hand this in to the TA at the end of the field trip.
1. Compare: a) the high-level meander terrace of the Newman Arboretum,
b) the lower terrace at the vine and hedge collection, and
c) the lowest terrace in the wildflower garden.
Briefly list three lines of evidence that would help us to determine the relative ages of these three
meanders.
2. What is the approximate age of the bedrock in the Ithaca area (circle one)?
350 million years
350,000 years
70 million years
70,000 years
20 million years
20,000 years
12 million years
12,000 years
3. What is the approximate age of the glacial deposits that we see on this field trip (circle one)?
350 million years
350,000 years
70 million years
70,000 years
20 million years
20,000 years
12 million years
12,000 years
4. What is the approximate elevation of the earliest formed meander scar that we saw on this
field trip (circle one)?
782 feet
900 feet
850 feet
980 feet
870 feet
5. What is the base level for the portion of Fall Creek that we saw on this field trip?
6. Is there a relationship between ancestral (pre-glacial) Fall Creek and the formation of the
meander scars on the various stream terraces on the present day Fall Creek. If yes, why?
7. What is the evidence that a valley of an ancestral (pre-glacial) Fall Creek existed prior to the
last ice age?
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