In addition, they eat themselves away from within as acidic fluids weaken the rocks. Even shield volcanoes can collapse. More than 50 huge submarine landslides are recognized around Hawaii. They show up as bright in these sonar images. In sonar and radar images, bright means rough, since signals are reflected back at all angles.
Smooth areas show up as dark since signals mostly bounce away from the source.
Calderas Crater Lake, in Oregon, marks a different sort of volcanic collapse, a caldera . About 6,000 years ago, a huge eruption blasted out so much material that the volcano could no longer support its own weight and caved in. The pre-eruption volcano, called Mount Mazama, was probably about 12,000 feet high. It was high enough to support glaciers, because glacial deposits are found beneath Llao Rock, the cliff on the left side. The cliff actually marks a former glacial valley filled by a lava flow that also spread out on either side of the valley.