Crumbling volcanic cone once caused catastrophic wave
A volcanic eruption can be wildly destructive event. Even after the magma has cooled and the smoke cleared, the resulting volcanic cone can still create an awesome show of force. The full extent of that potential is hard to imagine, but when a nearly 9,000-foot summit becomes unstable along its heat-blasted ridges, huge portions of the mountain can collapse at once. The island of Fogo was home to such a collapse, where an estimated 40 cubic miles of rock were dropped into the sea, triggering a tsunami almost 700 feet tall.
Numbers like that sound absurd without something more headline grabbing, like an asteroid, being involved. But dropping half a mountain into the sea at once can displace a considerable amount of water, and has likely happened semi-regularly in the Earth’s history. For specific evidence of the event in Fogo, researchers have been investigating a boulder on a different shore, some 30 miles away. The boulder’s makeup didn’t match any of the surrounding rock, but was a match for the rock from Fogo. They were then able to date the rock’s arrival on the shore through the amount of helium-3 that had built up thanks to sunlight reacting to olivine in the boulder. All this narrowed the boulder’s arrival to 73,000 years ago.
What size wave?
This confirmation allowed the researchers to reverse engineer the wave necessary to move the 770 ton rock to its current resting place. For the rock to be moved 2000 feet from the water, 650 feet above sea level, there must have been a wave that could reach the top of the Eiffel Tower. While the the shoreline has since changed through less dramatic tectonic movements, and the sea levels have risen as well, researchers now have a better understanding of what patterns and indicators to look for not only to find evidence of more collapses in the past, but possibly predict potential tsunami triggers in the future.
My first grader asked: Do we live close enough to the ocean to worry about a mega-tsunami?
While we do need to be ready for possible earthquakes and therefore tsunami activity in our region, we’re miles from the actual shoreline. We also lack any nearby volcanic islands off our coast, although other seismic activity to our north has definitely been known to cause some amazing amounts of flooding, albeit without the boulders.
Source: Island boulders reveal ancient mega-tsunami by Emma Brown, Nature News