Paddling the Susquehanna
River Trail is Still Getting Easier
By John Capwell, Resident Geologist and Social Commentator
Paddlers
rejoice!!!!! The water flowing out of the North Branch of
the Susquehanna is flowing faster than the previous year making it easier
to paddle the Susquehanna River Trail. Each
year the area from Tunkhannock, and north, in the Susquehanna watershed continues
its increase in elevation. Now since water runs downhill faster when the hill
is higher - - - - well you get the idea. Now of course we are assuming that there is
the same volume of water each year. This
elevation change has been an ongoing event for the past 22,000 years, give
or take 2,000 years.
About 25,000 years ago the massive glaciers that were the
hallmark of the last ice age covered Northeastern and Northwestern Pennsylvania.
Conservative estimates on the thickness vary but some Pennsylvania
geologists estimates put the thickness of the Ice Age glacier at Tunkhannock
at approximately 3000 ft. and upwards to 5000ft. at the Pennsylvania/New York
border. Now of course the question is, “How does an Ice Age glacier make the
water flow faster 22,000 years later?” Well it’s like the time your mother-in-law (yea
the big person in your life) got out of your canoe while it was still floating.
Remember how the canoe suddenly rose an additional six inches out of the water.
So where is the connection
between your mother-in-law in the canoe and a continental glacier, other than
the fact that they share the same core temperature? Glaciers are massive and as they age the snow consolidates, just
like an ice ball, under the pressure of each subsequent snowfall. The snow
that falls on the top of the glacier has a very low density but as each subsequent
layer is added, the snow crystals are pushed closer to each other. The result
is greater glacial density. The occasional snow melt that then refreezes,
cements the crystals together and further squeezes air from between the snow
crystals. So a glacier’s density increases as one moves from the top of the
glacier to the bottom of the glacier. (I am practicing mother in law restraint
at this moment)
The average density of a glacier
is in the neighborhood of is about 850 grams per liter or 1700 grams per 2
liters of volume for the average glacier (think two liters of soda). Those
1700 grams are equal to a little over 3.7 lbs. (I will gladly share all of my calculations with you if you are in need
of an insomnia cure). For a column
of 2 liter bottles, the mass of ice is 17,086.3 pounds. Per acre the pressure of a 3000-foot high glacier
is now 1850330.5 tons. Per square
mile the pressure now becomes 1,184,211,527 tons. Even at a 10 % error rate,
this exceeds 1 billion tons per square mile. Extending this over the Susquehanna River Trail watershed, north
of Tunkhannock, creates a massive pressure that literally depressed the Earth’s
crust. Today the elevation at Tunkhannock
is approximately 100 feet higher than it was 22,000 years ago. This increase
in elevation continues today albeit at a slower rate. And as we look north
of Tunkhannock, the pressure on the Earth’s crust was not only greater but
the subsequent crustal rebound is also more. So this year put your mother-in-law in her own kayak or canoe and
make sure she is wearing her life jacket.
You will have a sense of satisfaction as you shove her and her watercraft
out onto the Susquehanna River Trail. Even more so since she will travel down the Susquehanna faster since
this year Tunkhannock is 3/50” higher than it was last year. So the water
runs downhill faster and paddling the Susquehanna River Trail gets easier
every year. Let’s conveniently ignore that
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