Mount Thielsen, Oregon, USA
U.S. Geological Survey photo by W. E. Scott (fair use policy)
Mount Thielsen is the next peak in the Cascade Range north of Crater Lake, Oregon. It shows what happens to volcanoes once they finish erupting—in this case, glaciers have been making quick work of it in the last 300,000 years. During many different cold periods, snow accumulates into ice and begins to scoop out spoon-shaped cirques in the sides of the volcano. Although we're in a warm period these days, there's still a small permanent snowfield on Mount Thielsen known as Oregon's most southerly glacier.
The central plug of the Thielsen volcano makes a spectacular sight. It has been sculpted nearly into a horn as cirques excavate their way toward the heart of the mountain. This peak is called the lightning rod of the Cascades. Although Thielsen's structure is laid bare in the most recent main volcano, the surrounding rocks that document its earlier history are obscured by a thick blanket of ash from nearby Crater Lake, the volcano formerly known as Mazama.
More pictures from the Cascades Range
