Enormous quantities of water released from melting glaciers carved this gorge in less than 500 years. Almost all of New York had been covered by a mile-thick layer of ice. As the climate warmed and the ice front retreated, large pools of meltwater collected in lowland areas. Thirteen thousand years ago Glacial Lake Iroquois covered the basin now occupied by Lake Ontario, and the only path for water to drain from the Great Lakes to the sea was through the Mohawk Valley. The glacial Iro-Mohawk River carried over 100 times the flow of today's river, a torrent that quickly wore through soft shale and formed the deep gorge. Flows through the Mohawk Valley dropped dramatically once the ice retreated north of the Adirondack Mountains, allowing Lake Iroquois and the upper Great Lakes to drain through the Champlain and Hudson Valleys and later through the St. Lawrence Valley. The early Iro-Mohawk covered a wide area, and the river's surface would have been several feet above head level. Meltwater soon eroded a slot in the rock that captured all of the flow. Today's wildest floods fill only a small portion of the gorge carved by the Mohawk River's mighty ice-age predecessor.
