Mount Griggs, Alaska, USA
Photo by Robert McGimsey, U.S. Geological Survey (fair use policy)
Mount Griggs sits in the Katmai area of the Alaska Peninsula. In 1912 the Katmai eruption, the most voluminous one of the 20th century, covered the sides of Mount Griggs with a thick layer of ash. If you weren't careful, you might study a volcano like this one and assume that the ash came from it.
Griggs has not erupted in recorded history, but it still is quite alive. Its clean shape is one clue; another is the roar of gases coming from fumaroles near its peak, which can be heard from the valley below.
