More than 80 percent of Earth's volcanic activity takes place underwater, but we don't know as much about it as we do about volcanic activity on land. It would be nice to change that, since underwater volcanoes and earthquakes can cause damaging tsunamis.
In 2014, scientists installed a string of underwater sensors to gather real-time data about seismic events on the seafloor for the first time. And just a few months after the sensors went online, the Axial Seamount erupted off the west coast of the U.S. Researchers were able to watch exactly how the magma under the volcano moved and deformed the seafloor.
The sensors also detected earthquakes happening more and more often ahead of the eruption — up to thousands of little ones every day. And researchers found they got more frequent during low tide, when there was less water weighing down on faults in the seafloor.
We've suspected tides could help trigger some types of earthquakes for years. The effect isn't huge, but it's enough to measure, and it could be very useful. When tsunamis can cross the Pacific Ocean in just a few hours, every bit of early warning helps.