When an ash island formed in the Pacific Ocean following an underwater volcanic eruption in late 2014, scientists predicted it would soon disappear. Over the next six months, the island nestled between two others of the Tonga nation experienced heavy erosion, but "then it leveled off," NASA scientist Dan Slayback explains in a video. Three years later, Hunga Tonga-Hunga Ha'apai remains—reaching 400 feet above the ocean and covering almost 500 acres—and is predicted to last anywhere from six to 30 years, according to a new NASA study. It's an exciting development for a couple of reasons: First, scientists say the mass presents the first opportunity in the satellite era to carefully study how such islands form, per the Guardian. Second, the island could help scientists learn more about similar eruptions far away on Mars.
"Everything we learn about what we see on Mars is based on the experience of interpreting Earth phenomena," says NASA's Jim Garvin. "We think there were eruptions on Mars at a time when there were areas of persistent surface water," he adds, noting the new island could indicate whether Mars' thousands of volcanoes erupted beneath lakes or oceans, per the New York Times. NASA scientists, who've been monitoring the island monthly since its birth using radar and optical sensors, also hope to discover why it hasn't disappeared as predicted. A specific chemical reaction is suspected: In the case of the volcanic island Surtsey, formed near Iceland in 1963, warm seawater mixing with ash created a tougher rock than normal. A researcher notes the islands surrounding Hunga Tonga-Hunga Ha'apai also have "some pretty tough substrate." (Mars also has what look like scratches.)