Using sea-floor mapping technology during research cruises, the scientists found 12 volcanoes beneath the sea surface, some almost 10,000 feet high, and 3-mile-wide diameter craters left by collapsing volcanoes, a release from the survey group said Monday.
The researchers also identified seven active volcanoes visible above the sea as a chain of islands, it said.
Researchers say the findings are important for understanding what happens when volcanoes erupt or collapse under water and their potential for creating serious hazards such as tsunamis.
"There is so much that we don't understand about volcanic activity beneath the sea -- it's likely that volcanoes are erupting or collapsing all the time," survey researcher Phil Leat said at the International Symposium on Antarctic Earth Sciences in Edinburgh, Scotland.
"The technologies that scientists can now use from ships not only give us an opportunity to piece together the story of the evolution of our Earth, but they also help shed new light on the development of natural events that pose hazards for people living in more populated regions on the planet."
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