A February 1991 photo showed the opening as a circular structure about 1.6 square miles in area. In the October 1991 image, the opening is irregular in shape and measures about 3.9 square kilometres.
Also, in the later photo, the sides of the hole were shallow and the hole was filled almost to the brim. Researchers believe that in the eight months between the two images, a lava lake formed in the vent. Whether that lava was still liquid or cooled and solidified, they didn’t know.
“What we can show indisputably is that a vent has widened and appears to have gone from conical and hundreds of feet deep to an inner flat almost filled from the inside,” Herrick said.
“Our interpretation is that there was a new outflow of magma into a chamber below the vent, and this created a wider, irregular caldera that still contained an active lava lake when the second image was taken,” Herrick said. A caldera is a large cavity that forms when a volcano erupts and collapses.
“While it is possible that vent collapse was not associated with active volcanism, a collapse of this magnitude on Earth is usually associated with some form of magma movement, so we think that is likely the case here as well. The case,” said Scott Hensley, scientist. Researcher at NASA’s Jet Propulsion Laboratory who specializes in radar imaging and is the second author of the new study.
