By Glenn Coin | gcoin@syracuse.com

This   satellite photo   snapped last month gives a great geography and environment lesson on Oneida Lake.   The photo shows the eastern half of Lake Ontario and the Finger Lakes. What jumps out about Oneida Lake, referred to appropriately as "the thumb," is that it's the only lake covered in ice.   That's because Oneida Lake is so shallow compared to the others. It has an average depth of just 22 feet; some of the Finger Lakes are hundreds of feet deep.   If you're interested in a more detailed geology lesson, keep reading. I've posted a story I wrote in 1999 on the lake's geology.   The bottom of the lake - the entire lake itself - was set in place as glaciers from the last Ice Age melted. They scoured deep holes in the ground, including Oneida Lake, Green Lake and the Finger Lakes. 

The other lakes have more dramatic histories than Oneida. Green Lake, which is 180 feet deep, was gouged by a waterfall that rivaled Niagara Falls. The Finger Lakes were chiseled much more deeply: 300 to 400 feet.   Oneida Lake is much shallower: 55 feet at the deepest point, with an average of 22 feet.   "It's another small, glacially scoured basin," Hand said. "I can't think of anything particularly exciting about it."

Oneida Lake is a tiny piece of Lake Iroquois, a much larger body of water that formed 12,000 years ago, before humans had entered the New World. As the Ice Age ended, a glacier blocked the St. Lawrence River and flooded vast sections of what is now upstate New York. When the earth began to warm again, the lake drained into the Atlantic Ocean, leaving Oneida Lake behind.   Oneida Lake lies between two long rises in the landscape, called escarpments. The two escarpments - which one geologist referred to as "speed bumps" - are made of harder rock than the area between.   The lake's geology has shaped its history and its present. Along the south shore, where farmers drained swamps that extended all the way to Route 5, the fertile soils supported - and still support - a booming farming industry. Along the north shore, where sandy soils made farming a marginal operation at best, glass factories sprang up in Cleveland and Jewell to melt the silica in the sand to make jars and bottles.   The Cleveland glass factory employed several hundred people, and 150 worked at a factory in Bernhards Bay.

The length of the lake lies west to east, which means the prevailing west winds whip across its surface. That pushes the sand eastward, which is why the lake's biggest beaches - Sylvan Beach and Verona Beach - rest at the eastern edge.

As the glaciers retreated, they carved the lake bottom unevenly. Areas of shoals pop up around the lake. The largest, Shackleton Shoals, rises nearly dead center and ranges in depth between 6 and 26 feet. It's a popular fishing spot.

"It's a condominium for fish," said Tony Buffa, a fishing guide on the lake for 26 years.

The shoals can be treacherous for boaters. The highest point of Messenger's Shoal, in the eastern half of the lake, is just 1 foot below the surface. The aptly named Blind Isle is just 3 feet down.