39 Degrees and Holding: An Earthcache
Cayuga Lake Geologic History
The Finger Lakes originated as a series of south-flowing rivers
that existed in what is now central New York State. Around two
million years ago the first of numerous continental glaciers
advanced southward, initiating the Pleistocene glaciations,
commonly known as the Ice Age. The Ice age was really a series of
many advances and retreats of glaciers.
The Finger Lakes were carved by several of these episodes of
glacial scouring. Ice sheets more than two miles thick flowed
southward, gouging deep trenches into these river valleys. Whereas
streams only erode as far down as sea level, glaciers are able to
erode more deeply. The bottoms of two of the Finger Lakes (Lakes
Seneca and Cayuga) are actually below sea level.
In addition, as the glaciers advanced, they pushed great
quantities of soil and rock ahead of them, like giant, slow-moving
conveyor belts. When the ice sheets began to melt and retreat, they
left these vast deposits of material behind. This glacial till
material dammed the stream valleys at their southern end. The
valleys then flooded to form the Finger Lakes.
Ithaca Park is located at the south end of Cayuga Lake. Cayuga
is the longest and the second deepest of the Finger Lakes at 38
miles long and 435 feet deep. The bottom of the lake is 53 feet
below sea level at its deepest spot. The actual depth of carved
rock is well over twice as deep, but it has been filled with
sediments.
That’s nice. So, how about today?
During the summer, the lake’s surface heats up, but because the
lake has been carved so deeply by the glaciers, not all of it is
warmed by the rays of the sun. At 250 feet deep, the waters
maintain a year-round temperature of about 39 degrees
Fahrenheit.
Why would I care about that?
What is interesting is that this geologic process has created a
natural resource with the capacity to provide cooling without the
use of fossil fuels or CFC refrigerants.
Geothermal, or heat exchange systems are heating/cooling systems
that use the relatively constant temperature of the earth to heat
and cool homes and businesses with much less energy input that
boilers, furnaces or air conditioners. At its simplest form,
geothermal systems typically use pumps to move water heated or
cooled from the earth into buildings.
As an innovative ecological alternative to traditional air
conditioning, Cornell University replaced almost all of its central
cooling units, full of CFCs and drawing enormous electrical power,
with a system that cools campus buildings by drawing naturally-cold
water from the glacially-carved bottom of Lake Cayuga, returning
the slightly-warmer water to the naturally-warm shallows of the
lake. The system is not your typical air conditioner. Every minute,
7,000 gallons of cold water from the bottom of Cayuga Lake travel
to the shoreline through an underwater and underground pipe system,
cooling a separate closed water loop that goes up to campus,
cooling buildings.
Since it went online in 2000, the Lake Source Cooling system has
reduced the amount of power used to cool campus by 85%-90%. That’s
about 20 million-kilowatt hours of electricity per year which is
enough power to serve 2,500 homes a year. It has also permitted the
University to eliminate all six of the old chillers which used CFCs
(about 35,000 pounds of CFCs). Using this geothermal system reduces
the emission of greenhouse gases and reduces the current use of
CFCs which depletes the earth’s ozone layer.
Wow. How does that work?
LSC consists of two loops, one carrying water between the lake
and the LSC plant on shore and one closed loop between the plant
and campus. The Cornell water and lake water never mix. Once on
campus, the second loop of water chilled by the lake winds through
pipes and collects heat removed by air conditioning in the
buildings.
The onshore LSC plant. (which can be seen across the street
while standing in the park at the coordinates), pumps the 39-degree
Fahrenheit lake water to a heat exchanger, where it absorbs some of
the heat from the closed loop from Cornell, before the water
returns to the lake. The 55-degree Fahrenheit water enters the lake
at a shallow depth. The last 100 feet of the outfall has diffusers
on it — 38 nozzles that are small in diameter that direct the water
and also induce lake water to mix with it, so it quickly returns to
the ambient condition. The actual amount of heat added back into
the lake is equivalent to two additional hours of sunlight each
year.
The open lake loop starts at an intake pipe 250 feet below the
lake surface, 10 feet above the lake bottom in water, approximately
two miles into the lake from where the coordinates take you.
If you would like to learn more about how the system works,
check out Cornell’s page at:
http://www.utilities.cornell.edu/utl_ldlsc.html.
To Log this Earthcache you need to complete the following
tasks:
- Take a photo of yourself with your GPS at the pavilion at the
park with the lake in the background.
- Bring a thermometer with you. Scoop a cup of water out of the
lake from the surface and use the thermometer to estimate its
temperature (please use a cup to avoid dropping your instrument
into the lake!). If the lake edge is frozen, do not try to access
the water; just assume 30 degrees for your work. Based on the
information above, determine the temperature difference between the
water at the surface of the lake and the water at 250 feet.
Calculate the drop in temperature per foot of water.
- In your log, post your photo and your math.
- Send me an email with the answer to the following question:
What geological process is responsible for steady temperatures deep
within the lake?