Volcano Minute — Using ocean noise to monitor for volcanic eruptions

Aloha, it's your weekly Volcano Minute, brought to you by the USGS Hawaiian Volcano Observatory. 

Out in the open ocean, waves are constantly rolling and crashing. That motion creates a steady, rhythmic beating on the seafloor. Those vibrations travel through the Earth and are picked up by seismometers around the world, including here in Hawaii. 

Most days, scientists at the Hawaiian Volcano Observatory ignore this ocean noise and focus on the signals coming from inside our volcanoes. But recently, that constant ocean hum has been used as a new volcano monitoring tool. 

Using a technique called ambient noise interferometry, scientists measure how fast those ocean‑generated signals pass through the ground. When the speed changes — either slowing down or speeding up — it can tell us something about what’s happening beneath a volcano’s surface. 

Two months before Kīlauea’s 2020 summit eruption, ocean noise signals began slowing down between stations on opposite sides of the summit caldera. As magma rose toward the surface, it cracked the surrounding rock. Those cracks made the ocean‑driven vibrations travel more slowly.  

During ongoing episodic eruption at the summit of Kīlauea, scientists see the opposite effect along the caldera rim. As magma accumulates in shallow storage zones, it pushes outwards, closing existing cracks. With fewer cracks for vibrations to navigate, the signals speed up — giving us an early clue that a fountaining episode might be on the way.  

This technique is still evolving, but the results are promising. The next time you hear the ocean’s steady thrumming, know that it’s giving scientists another window into the hidden movements of magma — helping to forecast when the next fountaining episode or other eruptive activity at Kīlauea might begin.  

Mahalo for listening, I’m Katie Mulliken and this was your weekly volcano minute brought to you by the USGS Hawaiian Volcano Observatory.