Wallowa Lake - Geology and Formation

Geology and Formation

Wallowa Lake has been used in Geology text books as an example of a lake dammed by moraines. These moraines begin well below the water's surface and climb to over 900 ft (270 m) above the lake. Before the glacial till compounded enough to form the moraines that currently surround the lake, a large alluvial fan was present in the valley. This fan was created by the Wallowa River transporting debris into the valley. The sediment left by the river was pushed by a series of glaciers that advanced north into the valley. As they pushed the debris, they also dug deep into the earth. Though the number of glaciers that formed the moraines is debated, but the most accepted hypothesis is that eight or nine glaciers formed the walls that now dam the lake. The last glacier advanced into the valley about 17,000 years ago and is known as the Wallowa Glacier. Its moraines form much of the lake shore. Near Glacier Lake, high in the surrounding mountains, is evidence of several subsequent glacier advances. Occurring subsequent to the formation of Wallowa Lake, these did not reach the location of the lake. The oldest of these was 11,000–10,000 years before present.