Large volcanic eruptions can temporarily cool Earth's climate and, a team of scientists now suggests, lower sea level worldwide.
The tiny particles of broken rock and droplets of condensed gases that a volcano ejects high into the atmosphere reflect sunlight into space. So, after an eruption, there's less radiation reaching Earth's surface to warm it, says John A. Church, an oceanographer at the Commonwealth Scientific and Industrial Research Organization in Hobart, Tasmania. In the wake of a major eruption, this deflection of solar energy can cause global air temperatures to drop below average for months.
New analyses by Church and his colleagues suggest that these chilling effects influence the oceans as well. The water would contract as it cooled, with a concomitant drop in sea level.
To estimate the effects of volcanic eruptions on sea level, Church and his colleagues used tide data from around the world, ocean temperature and salinity data gathered by ships, and climate models that include both the atmosphere and the oceans.
After each of several major 20th-century eruptions--including those of Indonesia's Mount Agung in 1963 and the Philippines' Mount Pinatubo in 1991--the oceans cooled subtly for about 18 months, and sea level dropped, on average, several millimeters, or about three times the thickness of a penny. As natural processes scoured the volcanic material from upper levels of the atmosphere, the amount of radiation reaching Earth's surface …