Devil’s Hopyard State Park :
Footprints of the devil?
The Eightmile River (which is not eight miles
in length but rather it is eight miles upstream from the mouth of
the river in Old Saybrook) cascades over Chapman Falls the
Devil’s Hopyard State Park in East Haddam, CT. The
fall, Chapman Falls, drops about 60 feet in a couple of falls and
rapids. In the process, it has drilled several spectacular
potholes. This EarthCache investigates those potholes.
The interested cacher can find a description of the geology of the
Devil’s Hopyard on-line1 along with a trail
map2. It is recommended you download the trail map so
you can explore other interesting areas of the park when you have
completed this EarthCache
1.
http://www.ct.gov/dep/cwp/view.asp?a=2716&q=325126&depNav_GID=1650
2. http://www.ct.gov/dep/lib/dep/stateparks/maps/devilshopyard.pdf
Purpose: This EarthCache is
published by the Connecticut Geological and Natural History Survey
of the Department of Environmental Protection. It is one in a
series of EarthCache sites designed to promote an understanding of
the geological and biological wealth of the State of
Connecticut
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Directions: The gate at Devil's
Hopyard State Park is open from April 1 until December 1.
From CT Route 9: take Exit 7, then a left at
the end of the exit ramp onto CT Route 154 north. Take a right at
the first traffic light and follow the signs.
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From Interstate 395: take Exit 80 west. Take a
right onto CT Route 82 west. Take a right onto Hopyard Road and
follow signs.
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From I-91S: take Exit 22. Take Route 9S, Exit
10. Take Route 9AS to Tylerville. Take Route 82E over CT River for
about 3 miles. At the stop sign take a right, and then take
immediate left. Follow that road for approximately 8 miles, then
follow the signs. Parking Lot: N. 41o 29.0400’
-072o 20.5490’
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Long Description: Chapman Falls
cascades over iron-sulfide bearing schist and gneiss of the
Brimfield Formation. Weathering of the iron sulfide minerals
in the ledge gives a rusty color to much of the rock (see left side
of Figure 2A). Weathering of the iron sulfide makes the rock
less resistant to erosion. The iron sulfide dissolves and
iron oxide (rust) precipitates nearby. This creates small
holes in the rock that water and ice exploit during the erosion
process. Some of the layers, however, do not have the
iron-sulfide minerals. They are more resistant to
erosion. Chapman falls cascades over both rusty and non-rusty
(i.e. the iron-sulfide minerals are not part of the rock) gneiss
and schist. The face of the outcrop over which the river falls is a
major fracture, possibly a fault. Rocks to the south of the
fault were removed by weathering and erosion, leaving the resistant
cliff to form the waterfall.
Location: N. 41o
29.0286’ -072o 20.5026’
The above location should take you to the west
side of the falls at an observation area. Observing the
waterfall one must be impressed by the potholes scattered over the
ledge in the bed of the river (Figure 2B-D). The largest we
have seen (Fig. 2B) is about 3 feet (1 meter) in
A.
B
Figure 2. Chapman Falls at the top
looking down. A. Large pothole near top of falls.
Pothole diameter is about 3’. B. Notice pothole
behind the red colored bush.
C.
D
Figure 2. C. Half a pothole on
the side of the cliff where water does not flow today.
D. Intersecting potholes. Note that current does not
run through the potholes; rather they are merely filled with
water.
width. The potholes are up to 6 feet
(two meters) in depth. Leary (2004) reports potholes up to 25
feet deep. Those deeper potholes may have been covered by
water during our visits: we did not see them. Legend has it
(Leary, 2004, p.67) that the pot holes were formed by the devil
himself when he accidentally got is tail wet at Chapman
Falls. In his rage he stomped all over the falls, his flaming
hooves carving the potholes in the river bed.
Geologists prefer to think, based on
observational data, that potholes are formed by the drilling action
of swirling water and rocks. Refer to the diagram below.
They originate at a location of a persistent eddy where a
river flows over bedrock. Water-power swirls small and large
grains of sand and rock that persistently bounce around
in the eddy and gradually chip a hole into the ledge. Sand
and rock are tools in the drilling action. As the hole gets
drilled deeper it tends to trap rocks in the hole and ultimately
breaks the drill-implements into smaller and smaller fragments.
Although the potholes are in the river-bed today it
is doubtful that they are actively being drilled. One telling
bit of evidence is the half pothole
(Figure 2C) perched high and dry, well above the water
level. Those potholes in the river channel seem to be out of
the eddies and are merely filled with water as shown
here. These observations suggest that the potholes were
drilled at some time in the past when water flow was dramatically
greater. Formation of the potholes probably occurred during
the melting of the Ice Age glaciers when torrents of meltwater may
have coursed down the Eightmile River drainage. The doubtful
cacher may respond, “But maybe it all happens only during
flood stage.” And, you know what? The doubtful cacher
may be right for some of the potholes in the middle of the stream
bed. Maybe the potholes illustrated in Fig. 2A, B, and D are
actively being deepened during flood events. It is hard to
imagine, however, that the river would ever have enough water to
actively drill the pothole illustrated in Fig 2C.
A dry waterfall may be found just a few
hundred feet to the east (N. 41o29.032’,
W.072o20.451’ ). Along the
way be sure to view the potholes from the other side of the
river.
A.
B
Figure 5. Dry waterfall just to east
of Chapman Falls. Image on left taken from road looking down
the fall. This watercourse flows only during high flow stages
of the river. Image on right shows very large circular
depression located at base of dry fall. It may be a pothole
or perhaps a plunge pool.
Figure 5A shows the dry water-fall from the
road at the top of the falls. Notice the water sculpted rocks
and incipient potholes. If you walk around to the bottom of
these falls (not handicapped accessible) you will come upon
a large pothole-looking feature (Figure 5b). This may a
plunge pool rather than a pothole. Can you suggest reasons
for this idea? This waterfall is not always dry according to
park personnel. Water, during high flow events, overflows the
normal channel of the Eightmile River and falls over the dry water
fall.
The late Dr. R. F. Black from the University
of Connecticut once hypothesized that the potholes were drilled
when glacial meltwater poured through a hole in the Ice Age Glacier
and carved the potholes and plunge pool. The downstream
canyon was eroded at that time. That hypothesis would explain
also the reason the falls are located where they are.
Reference:
Leary, Joseph, 2004, A Shared Landscape: A
Guide and History of Connecticut’s State Parks
and
Forests. Friends of Connecticut State Parks, CT D.E.P,
and CT Forest and Park Association, Hartford, CT, 240p.
How to log this EarthCache:
Provide an answer to the above question and submit a picture of you
and/or your companions in front of the plunge pool/pothole
illustrated above (Fig. 5B). If you cannot make it to that
location, submit a picture near the east side of Chapman Falls,
showing you and/or your companion with a visible pothole in the
picture.
Difficulty. 1
Terrain. 1
(This is handicapped accessible)