Mauna Loa and Mount St. Helens erupt in different ways,” said Liz Westby, a geologist based at the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Washington.

Washington's Mount Rainier and Sicily's Mount Etna also made the list. Perhaps most interestingly, Mauna Loa has some competition for the crown of the largest volcano — that is, on the Earth's ...

Arsia Mons, the southernmost of the Tharsis Montes trio, stands at an awe-inspiring 20 kilometers high, dwarfing Earth's tallest volcano, Mauna Loa, which rises 9 kilometers above the seafloor.

Mount Adams in Washington state is seismically calm. But a flurry of earthquakes around the volcano has garnered attention from observers wondering whether it will blow.