Volcanoes! The U.S. Geological Survey believes that 55 of our 169 active volcanoes pose a high or very high threat to people. And the threat is not only molten lava; volcanic gas and falling boulders have also killed people.
We do monitor well-known volcanoes such as Hawaii’s Kilauea, Washington’s Mt. St. Helens, and Wyoming’s Yellowstone. But there are many that are not well monitored. Almost half of the active volcanoes in the country don’t have adequate seismometers—tools used to track the earthquakes that often occur during volcanic eruptions. And even at the sites that do have seismometers, many instruments—selected because they are cheaper and consume less power—are unable to take a complete record of the ground shaking around an eruption, meaning “the full amplitude of a seismogram may be ‘clipped’ during recording, rendering the data less useful for in-depth analyses.