Why some volcanoes blow and others don't

BERKELEY, Calif., Nov. 26 (UPI) -- Geophysicists at the University of California at Berkeley may have figured out why some volcanoes pop and others ooze.

"One of the central problems of volcanoes is: Why do they erupt and why do they alternate between relatively benign effusive eruptions and destructive explosive eruptions?" Michael Manga, associate professor of earth and planetary science, said Wednesday. "This hypothesis helps us understand why it happens and how it happens."

Conventional wisdom holds in explosive eruptions only, rising magma breaks or fragments as it approaches the surface, releasing bubbles that blow the magma out like champagne from an uncorked bottle.

Manga proposes instead that fragmentation occurs in most if not all volcanic eruptions, though non-explosively.

In an explosive eruption, the magma rises fast, allowing a build-up of gas pressure within the gas bubbles that leads to rapid bubble growth, abrupt fragmentation, and an explosive release.

In effusive eruptions, he argues, continuous, repeated fragmentation during the magma's rise to the surface would break gas bubbles and allow the release of significant amounts of gas before the magma reaches the surface, leaving little for an explosion.