The Age of Ice
A preview from The Edgewalker's Guide to 20 great beaches on Lake Ontario to be published in 2002
Wolcott Falls, a public waterfall in Wayne County
Lake Ontario's shoreline lies in a land shaped by ice and water. Ours is a topography of kames, moraines, kettles, drumlins and prehistoric beaches. The vast ice sheet that covered this area 10,000 years ago continues to impact people's lives today. When the farmer discs and plants his field with the rocky knoll and the sandy patch or when the gardener struggles with cloddy sticky clay, they are reliving that glacial history.
The last ice age occurred between two and three million years ago and consisted of at least four major ice advances. The last of these was about 18,000 years ago and at that time ice completely covered present day Lake Ontario. It's believed that when it finally began to melt, it retreated considerably faster than it advanced. It's also known that the retreat was not a simple one way affair. There were milder spells and colder times when the ice paused and even re- advanced.
No one really knows for certain just what caused that first unusually cold snowy year when spring never came. Perhaps massive volcanic eruptions like that of 1815, "the year without summer" when Tamboro erupted in the East Indies and blew about 200 cubic kilometers of earth into the air, sent so much ash into the atmosphere that it blocked enough sunlight to tip the delicate global balance towards cooling. Or perhaps the ice ages were caused by fluctuations of solar energy output or maybe a gigantic meteorite slammed into earth and gave its planetary rotation enough of a jolt to impact solar energy inputs. In any event, glaciers form from snow. And the heaviest snow falls occur at temperatures not far below freezing, so it only took a slight drop in the overall average temperature on earth to initiate the last ice age. Geologists don't know for certain what triggered the last ice age. Nor can we assume it won't happen again.
Whatever the cause the amount of ice that came grinding and scraping and ever so slowly flowing across this landscape heading southwest from an origin somewhere around Labrador was almost inconceivable. The tremendous weight of the glacier actually depressed the earth's crust and caused it to tilt slightly toward the thicker ice to the north. Later as the ice melted and retreated the land bounced back to its original level. Because the ice was heavier to the north and slower to melt, it pushed the earth's crust down farther than it did on the lake's south shore. When the ice released the land, the more depressed crust to the north rose more quickly. This tilted the entire lake basin slightly from north to south. The effect of this was to lower the land and raise the water along the south shore to flood valleys previously carved by south shore creeks and rivers to form the half dozen present day south shore bays between Rochester and Oswego. When the ice first melted, the rebound was rapid ( It is still measurable from year to year in northern Canada.) Parts of the St. Lawrence valley rose several hundred feet while the land on the south shore rebounded over a hundred feet since the time of Lake Iroquois.
The glacier gouged out all the Great Lakes basins along with many other valleys and depressions. Then, when it began to melt, it dumped a vast load of gravel and rock along the edge of its furthest advance. This ridge of gravel and rocks, known to geologists as a moraine, blocked the lakes from draining south into the Mississippi. At first Lake Ontario drained southwest of Syracuse. Later it drained eastward through the Mohawk Valley as the St. Lawrence outlet was still blocked by ice. At that time the lake's level lay several hundred feet above its modern day level and its shoreline was considerably south of the present day shoreline. That shoreline's traces are still visible along old Ridge Road between Sodus and Lockport. The ridge of Ridge Road is actually an old beach berm thrown up by the waves of Lake Iroquois.
The last glacier, the Wisconsinan, reached all the way south into Pennsylvania at its maximum advance. As it moved across New York a very different flora and fauna from that of today followed it. The climate was much like today's Canadian tundra. Bones of musk ox, caribou, as well as those of other creatures like the wooly mammoth and the mastodon have been found in upstate NY peat bogs. People lived here too, and it's suspected that those mammoth hunters played a major role in the disappearance of some of the now vanished Pleistocene creatures that might have walked on the shore of Lake Iroquois.
When the melting glacier freed the St. Lawrence River channel, the drainage abruptly shifted to today's pattern and the lake level quickly dropped to its approximate present day level. At this time the land was still depressed from the glacier's weight and so lay considerably below its present level. In fact, the St. Lawrence and Lake Ontario were actually briefly below sea level for a time and it was then that the lake experienced its so-called marine invasion. Salt water along with a number of marine creatures entered the present lake basin. As the land rebounded from the ice's weight, the lake basin rose above sea level and the lake once again became a fresh water sea. However, some of the fish like the Atlantic salmon, the deep-water sculpin and the planktonic shrimp like animal Mysis managed to adapt to freshwater and remain in the lake today. Additional evidence of the marine invasion comes from seal and whalebones found in sand and gravel deposits in the St. Lawrence Valley.
During its marine stage, the lake's level was lower than it is today and the south shore lay considerably north of its present limit. This caused rivers and creeks to carve valleys into the land north of the present day shoreline that flooded a few thousand years later when the lake levels rose and the land tilted from rebound.
It was also the glacier that made the south shore cobble beaches so much more varied than those on the Canadian shore. When I first explored the northeastern coast of the lake during a cruise there with Ariel in 1980 I was immediately struck by the monotony of the beach pebbles here- they were nearly all gray. The beaches I had grown up near in Wayne County were a colorful mix of brown, gray, black, white, orange, and pink pebbles. We owe that variety to the glacier which brought us vast piles of glacial till and rocks from the Adirondacks and Canada as it advanced from the northeast. The till and these so called glacial erratics were carried hundreds of miles, then dropped when the ice melted. The land up near Chaumont, Henderson Harbor and the Canadian beaches and islands on the northeast side of the lake, missed most of the erratics and mountains of till. Here the glacier scraped the land clean and left the limestone bedrock stripped of soil. When it melted it left no debris. The beaches here are mostly made up of bits and pieces of their underlying bedrock and so are uniformly gray.
The glacier is also, of course responsible for the presence of the drumlin field that is so characteristic of the region between Syracuse and Batavia. These drumlins are distinctively sculpted hills of glacial till (an unsorted mixture that the glacier dragged along and dropped made of mostly sand, clay, rocks and boulders). They are all oriented roughly north south following the flow of the glacier and have a streamlined elongated appearance with the north ends being steeper and the south ends tapering gradually down. From the air they look a bit like streamlined nacelles or perhaps like a school of swimming fish.
Between Sodus and Oswego the drumlins meet the lakeshore and as that shoreline erodes and eats into these hills, the distinctive clay bluffs along this stretch of coast are created (see section on bluffs for more). This part of New York State has one of the largest groupings of drumlins found anywhere with over 10,000 tallied. They are a ubiquitous landform in much of Wayne County and this little literary work was written in a house perched atop a drumlin near the lakeshore.
While the thought of a mass of ice a thousand feet thick lying over where my house and word processor now exist strikes me as pretty grim, the fact is people adapted to and even thrived during the brutal conditions of the ice age. It has even been suggested that we may owe the beginnings of "civilization" to ice. The theory goes that people banded together and worked cooperatively to survive the brutal conditions of the ice age advancing language and technology to do so. While this may be tough to prove, there is another benefit of the ice that seems pretty clear and well documented that of its impact on soil fertility.
As the glacier pushed its vast weight across the land, it ground rocks into fragments and dust releasing minerals to the soil. These minerals contribute to what the author of 1902 Geography of New York State calls our "strong soils". Recently glaciated mineral rich soils are far more productive than are the leached out nutrient poor soils of the southern U.S. and the tropics. The theory goes that these northern soils nourished crops and those who ate them with minerals that were vital to our vigor and well being. Some historians have even gone so far as to attribute the success of the aggressive capitalistic northern European cultures that colonized and dominated this continent to well mineralized soils.
Many of today's gravel and sand pits, occasional bogs and some of our big swamps like the Montezuma marshes also owe their existence to the ice age and the shallow glacial lakes that were formed immediately after its retreat. And today when you hit that hard head in the north lawn with the mower, you can probably thank the glacier for it.
From the Edgwalker's Guide to 20 Great Beaches… watch this space for more on this latest work from Susan Peterson Gateley