Active volcanic activity is common in Lassen Volcanic National Park backcountry. This mud pot is in Bumpass Hell, easily reached by trail from near the summit. Lassen Peak, one of the worlds largest plug dome volcanoes, last erupted in May, 1914. Called a miniature Yellowstone by many, mud pots, fumaroles and boiling water continue to this day. Lassen is part of the Pacific Ring of Fire.