Scientists have uncovered a geological explanation for why some volcanic eruptions are more explosive than others.
The bubbles are the result of magma being rapidly cooled by water as it shoots out of underwater vents.
Mount St. Helens forms part of the Cascade Arc, a line of volcanoes that extends from British Columbia, Canada, to northern California
At least 25 people have been killed after volcanic ash buried homes and lava swept through villages.
The Ptolemaic Kingdom fell to the Roman Empire after the death of Cleopatra.
Prime Minister Shinzo Abe, who returned from the United States on Saturday, said he had ordered the military to help in rescue efforts
"Mount Fuji is now in a state of pressure," says a volcano researcher.
Closing airports, forcing 76,000 to evacuate, and killing two people, Indonesia's Mount Kelud is wreaking havoc on the island of Java