To really appreciate the Mohawk Valley it's essential to understand how it came to be.
I've read dozens of books describing the geology of upstate New York, and I've traveled the length and breadth of the Mohawk Valley trying to visualize the forces of nature that created this unique passage through a chain of mountains. It took awhile but I got it, and with the help of friends who have little interest in geology or what went on here thousands of years ago, I think I can help you get it too.
So, with the aid of your imagination and a shaded relief map, I offer the following:
Picture this. From Little Falls west is a huge lake, many times bigger than Lake Ontario, that covers all but the highest peaks. From The Noses east is another huge lake, many times bigger than Lake Champlain. At Little Falls is a ridge of solid rock. Not just any rock, but super-hard Adirondack rock that had pushed up through overlying dolostone and shale when the Adirondack dome started to rise 100 million years ago. Further east, in the area of The Noses, is also solid rock, part of a chain of mountains that run from Maine to Georgia--- the Appalachian Plateaus. In between is glacial till--- boulders, rocks, gravel and sand--- packed high and hard by a mile-high glacier.
That's how it was after the last glacier melted 10,000 years ago.
For a few thousand years the huge lake to the west,
now called Glacial Lake Iroquois, put enormous pressure on the solid rock
and glacial debris dam at what is now Little Falls. As the dam deteriorated,
the lake started to overflow, creating falls, rapids and a river of such
proportions they are beyond imagination. Their force was so great that
swirling water and chunks of glacier-deposited rocks and sand literally
ground holes in the underlying dolostone, creating huge potholes.
Take a look.
For eons the huge lake's outlet eroded a 25-mile
channel through solid rock and glacial till, breaching the Appalachian
Plateau at The Noses and pouring into Glacial Lake Albany.
Can't picture it? Look at this shaded relief
map of the Mohawk Valley. Follow the outline of Lake Iroquois. Look
at the narrow gaps at Little Falls and the Noses. See the Lake Albany basin.
Got it? If that's all you get out of this chapter you are
ahead of the game. However, there is much, much more. And it's fascinating......
....... if you have time and imagination.
Water, Water, Everywhere Water
Five hundred million years ago a vast, shallow ocean covered what is
now New York State. To the west a high plateau, to the east a range of
towering mountains --- rivaling the Himalayas of today --- eroded into
the ocean. For millions of years suspended particles of eroded rock
and dissolved minerals settled to the ocean floor. Over time, the pressure
and heat caused by the weight of overlying sediment, turned sand to sandstone
and carbonate minerals to dolostone and limestone. These layers of sedimentary
rock covered ancient granite-type rock.
For 50 million years oceans and landmasses rose
and fell, and primitive creatures populated and evolved on the ocean
floor. Brachiapods (clam-like), cephlapods (octopus-like), bryazoans (moss-like),
crinoids (single-stem plant-like) and trilobites (horseshoe crab-like)
lived, died and became part of the calcium-rich sediment that eventually
turned to limestone laced with the fossils of these ancient life-forms.
Under the ocean floor, salty seawater, laden with
dissolved silicates, dripped, trickled and percolated through layers
of dolostone to find cavities created by gas pockets. Under extreme heat
--- duplicated in laboratories today --- dissolved silicates formed quartz
which, depending on impurities and temperature, became chert or double
terminated quartz crystals.
Some 450 million years ago calcium-rich deposits
dominated ocean sediments, however, intermittent inflows of mud eroded
from the eastern mountains also settled to the ocean floor, eventually
forming thin layers of shale intermixed with thick layers of limestone.
Ten million years later mud from the eastern mountains poured into the
ocean basin to become deep deposits of shale.
The Appalachian Plateau
Around 330 million years ago two huge continents (proto-North America
and proto-Africa) collided, causing an uplifting of the compacted sediments
that once lay horizontal on the ocean floor. This uplifting continued for
more than 100 million years, causing heat and pressures that altered the
composition and shape of the sedimentary rock, sometimes folding, faulting
or turning it on end. Today this much eroded and often faulted Appalachian
Plateau is a chain of mountains that runs from Canada to Georgia, crossing
New York State north to south, and once crossing the Mohawk Valley between
Little Falls and The Noses.
The Adirondacks
Young Mountains From Old Rock --- Still Growing
Around 100 million years ago a hotspot formed in the earth's
crust under what is now northeastern New York. This extreme heat
changed the composition of the "old rock" and caused it to expand upward,
creating the Adirondack Dome.
Sandstone and other sedimentary rock covered the
Dome as it moved slowly skyward. Millions of years of erosion stripped
these softer rocks from the mountains and exposed the harder metamorphic
--- granite-gneiss --- rocks that erode more slowly. At lower elevations,
sedimentary rocks such as sandstone, dolostone, limestone and shale
were pushed upward, causing all these rock formations to angle down and
away from the mountains.
The upward movement of the Adirondacks continues
today at the rate of 2-3 mm a year. Fact is the Adirondack Mountains
are growing 30 times faster than the wind, rain, ice and snow are wearing
them away.
Intrusions of Adirondack rock also occurred at a
few lower elevation areas such as the outcrops near Middleville and at
Little Falls.
Mile High Glaciers, Ancient Lakes
and Mighty Rivers Sculpted the Land
The ice age in upstate New York began 1.6 million years ago and ended
a mere 10,000 years ago. Advancing and retreating glaciers, ancient
lakes and mighty rivers sculptured the land, left enormous deposits of
rock, gravel, sand, silt and clay . . . and created the Mohawk Valley.
Glaciers more than a mile high covered this part
of the state, leaving scars on the highest Adirondack peaks. As these
monstrous fields of ice moved south they tore Adirondack rocks from
the peaks. Some of these rocks were suspended in the ice, to be deposited
miles away when the ice melted. Most became part of a massive grinding
and conveying system. The weight of the ice and the abrasiveness of
"sandpaper" rocks imbedded in the bottom of the glacier, ground
boulders to rocks, rocks to pebbles and pebbles to sand .... and carried
them southward. When glaciers encountered softer sedimentary rock such
as shale, limestone, dolostone and sandstone, they were ground
to rocks, pebbles, sand, silt and clay.
Some 12,000 years ago when the glaciers started
to melt, suspended boulders (erratics) --- some 20-feet across and
weighing 100 tons --- and all those grades of ground-up rock
were deposited throughout New York State. At the southern terminal of some
of these receding glaciers, vast amounts of mixed rock, gravel, sand,
silt and clay --- glacial till --- were deposited. These moraines
created hills, ridges, valleys, kettle holes and lakes, and
changed the direction of rivers. One of these moraines changed
the direction of West Canada Valley. Prior to the ice age, the river flowed
southwest past the present village of Prospect, on to Holland Patent, along
the path of Nine Mile Creek and entered the Mohawk River west of Marcy.
Glacial till deposited in the Prospect area, blocked the stream's original
path and redirected it southeast through Trenton Gorge. (Outflows
from ancient glacial lakes had already started the formation of Trenton
Gorge when the river's direction changed.)
Glacier
Melt-Waters Create Trenton Gorge,Trenton Falls and Boonville Gorge
As
glaciers melted and receded northward, ice dams, glacier deposits and rock
formations held back vast areas of freshwater. These ancient lakes existed
for thousands of years and covered much of upstate New York. A
glacial lake in what is now the upper Mohawk Valley was so big and deep
that it filled the entire valley west of Little Falls and most of
West Canada Valley. The Hasenclever and Deerfield hills between West Canada
Valley and the Mohawk Valley were islands in that lake.
For a time one of the outflows from this lake ran
northwest through a gap near present day Trenton Falls.
Vast amounts of fast moving water, rocks and sand, passing
through this gap into a northern basin, cut into the limestone in this
area and started the creation of Trenton Gorge. Waterflow through the gorge
was later reversed when the southern lake dropped in level and the water
level in the northern basin ---- in the Forestport area --- increased.
For thousands of years enormous volumes of water, rock and sand passed
through this outflow, deepening the gorge. Water activity and ice
caused joints (deep cracks) in the limestone to widen, causing huge
sections to break loose, resulting in step-like formations topped
with resistant limestone, creating a series of magnificent waterfalls now
known as Trenton Falls.
Trenton Gorge and Trenton Falls (Kuyahoora) were created by glacial water. This is a view of Upper High Falls with Mill Dam Falls in the background.
Prospect Falls does not appear to be one of the Trenton
Falls. It's more likely a side of the gorge that was cut by a glacial outflow.
The other side was cut away by subsequent stream erosion and/or hidden
under glacial till.
Other
outflows of this northern lake determined the course of a number of
Mohawk Valley streams. A section of the river between North Branch and
Hillside, sometimes known as The Canyon, was created by this glacial lake
outflow, as was the steep-sided Boonville Gorge and its waterfalls. The
Lansingkill now follows the path of this ancient river. An outflow also
ran through present day Remsen and Barneveld cutting through limestone,
creating waterfalls and determining the course of Cincinnati Creek.
Another created Steuben Valley and set the path of Steuben Creek.
The Canyon between West Branch and Hillside was created by a glacial river.
Glacial meltwaters also created Frankfort
Gorge, Ilion Gorge, and the ravines, waterfalls and potholes on most of
the streams in the Mohawk Valley. Of course the greatest waterfalls and
potholes were at Little Falls.
A section of the Mohawk Valley, a Mohawk Castle, a British Fort,
a village and a creek were named after a pothole located in Canajoharie.
This pothole was famous long before the written word reached the valley.
Canajoharie describes "the pot that cleans itself."
Glacial Till Sorted By Lakes
and Rivers
Glacial river and lake-waters sorted glacial till. Rivers and streams
running into the lake carried rocks, gravel, sand, silt and clay.
The finer and lighter particles of clay were carried out into the
lake and settled to the bottom as clay deposits. Silt settled out
of the water closer to shore. Sand, gravel and rocks built up as deltas
near the mouths of rivers and streams. When these lakes and rivers
reduced in size, sorting continued, often depositing sand over clay, and
gravel over sand.
How Big Were They ?
It's difficult to comprehend the size and depth of the glaciers and
the glacial rivers and lakes that covered this area. It helps to consider
that the hills that start just north of Fairchild Road in Remsen and continue
south to Prospect and Hinckley, consist of rock, gravel and sand deposited
by a glacier. In addition to separating the glacial lakes in this area
and changing the flow of West Canada Creek, as noted earlier,
this glacial moraine contains a number of "kettle holes". These
conical-shaped holes, hundreds of feet across and dozens of feet
deep, were created when glacial ice, imbedded in the moraine, melted.
The melt-water drained through the till; gravity and erosion did the rest.
Similar deposits can be found in many areas of the Mohawk Valley.
Stand atop Deerfield Hill or Frankfort Hill or any
hill in the upper valley that is over 1300 feet above sea level.
Consider that all but these highest hills were covered by a glacial
lake. Look more closely at the lay of the land to see the terracing created
when the lake dropped to a lower level, remained there for many years,
and then dropped again and again as the downstream dam of ice and debris
eroded away.
Look at the hills on both sides of Boonville Gorge.
When the glacial lake to the north drained through this area, the glacial
river was as high as these hills. The volume of water and the amount of
rock, gravel and sand it carried was so great it created the gorge
and deposited millions and millions of tons of gravel and sand in the lower
valley. These deposits created a huge delta north of Rome. The Village
of Delta was built on that glacial river deposit. Today much of this
ancient delta is covered by Lake Delta. Further downstream this glacial
river deposited the sand that became the Rome Sand Plains.
Sand plains of various sizes were created by glacial
river deposits. These sand "deltas" became sand plains when the water receded
and the dry sand was spread by prevailing winds. There are sand plains
in the Town of Trenton and the Town of Norway. The largest sand plain
in the Mohawk Valley was created between Schenectady and Albany by the
outflow of Glacial Lake Iroquois.
Adirondack Rock More Resistant
to Erosion
While glacial lakes and rivers had a major impact on the lay of the
land and the direction of streams in the lower valley, it had far less
impact on the terrain of the Adirondack stretches of such tributaries
as West Canada Creek and East Canada Creek Although these mountain
valleys were widened and sculpted by the glacier, Adirondack rock --- mostly
granite-gneiss --- resisted glacial and glacial water erosion. The glacier,
however, tore boulders and rocks from the mountains, suspended some of
them in ice, or ground them to rocks, pebbles and sand. When the
glacier melted the larger rocks and boulders settled on mountain tops and
ridges, and in the valley. The rest were washed downstream.
Glacial meltwater and debris that plummeted down
waterfalls and through crevices in the Adirondack rock, dug small lakes,
ponds and potholes in solid rock. Most of the lakes and ponds in these
upper valleys and many of the deeper water areas in the tributary streams
were created or started at that time
The potholes in the rock outcrop in West Canada
Creek, three miles northwest of Nobleboro are examples of the grinding
power of volumes of water swirling small rocks, gravel and sand.
In this case it was --- and still is --- Adirondack rock grinding
Adirondack rock that created these unusually large granite-gneiss
potholes. The West Canada's Ohio Gorge was created when an upheaval of
granite-gneiss fractured. Repetitive thawing and freezing widened fractures,
breaking off huge chunks of rock. Glaciers and glacial water carried away
debris and further sculpted the half-mile long gorge.
What Was Left After It Was All Over?
When the ice age ended and the glacial lakes and rivers had all but
disappeared, the Mohawk Valley consisted of rock and ground-up rock.
In the mountains thousands of acres of solid granite-rock, huge boulders,
piles of rocks and sand dominated the landscape. In the lower valley dolostone,
limestone, shale, and sandstone with a couple of intrusions of Adirondack
rock was covered in most areas with mixed and sorted deposits of
rock, gravel, sand, silt and clay. In many areas hillsides and valleys
were littered with Adirondack rocks of many sizes, some as large as small
buildings.
The stage was set for life to return to the Mohawk
Valley.
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