Glacial Valleys

Glacial Valleys. Crater Lake National Park. The collapsed volcano that now holds Crater Lake once stood more than a mile (1.6 km) above the present lake level. Called Mt. Mazama, this massive mountain of overlapping cones was high enough to support a cap of snow all year. During the Ice Age, snow often blanked the entire mountain, more snow than the summer sun could melt. The accumulated snow compacted to form glaciers, sluggish rivers of ice that carved out broad valleys as they inched down the slopes., Eventually, the ice in the valleys melted. When the top of Mt. Mazama caved in about 7,700 years ago, the upper portions of the valleys collapsed with it. Today, you can see the remains of two “U” shaped glacial valleys on the caldera wall across the lake, Kerr Notch (left) an Sun Notch (right)., Graphic Illustrations: , 1. Alternating eruptions of lava and cinders built Mt. Mazama to its maximum height., 2. Glaziers formed on the upper slopes, growing larger during the Ice Age., 3. Climatic changes and more eruptions melted the glaciers, exposing the excavated valleys., 4. The collapse of Mt. Mazama truncated the glacial valleys, leaving “notches” still visible today.