In recent years, the ground under the lake has started to rise significantly, indicating increased geological activity, and parts of the national park have been closed to the public.
There is a 'bulge' about 2000 feet long and 100 feet high under a section of Yellowstone Lake, where there are a variety of faults, hot springs and small craters. Seismic imaging has recently shown that sediment layers are titled, but how old this feature is has not yet been established.
There is evidence of hydrothermal explosions at Yellowstone in the distant past, but no large ones during the past several thousand years.