An active volcano in Alaska has erupted again, raising the state’s aviation alert level to red.

The Alaska Volcano Observatory spotted an eruption of the Bogoslof Volcano in the Aleutian Islands at around 2:16 p.m. on Sunday, Bloomberg reports. The eruption, the most recent in six months of volcanic activity, lasted 55 minutes and sent a massive ash plume 35,000 feet into the air.

As a response, the Aviation Color Code has been raised to the highest level. Volcanic ash in the air can disrupt and even destroy jet engines flying above 20,000 feet. Flights between Alaska and the rest of North American and Asia are likely to stay grounded for the next few days.

Bogoslof Volcano is a submarine stratovolcano – a volcano that is conical, built up over several layers. The summit forms Bogoslof Island, which is on the Bering Sea. Since the volcano began erupting in December, the island has more than tripled in size. Bogoslof Island has grown to 242 acres and is expected to keep growing.

The last recorded eruption was on May 17, when ash clouds were seen rising as high as 34,000 feet.

Geophysicists are saying that the Bogoslof Volcano is providing exciting new research opportunities. Hans Schwaiger, a geophysicist with the Alaska Volcano Observatory, said,

It’s different from most of the other volcanoes we deal with. It comes through the ocean, and so there’s a different character to the plumes, there’s more lightning detection we’re getting off these so it’s an interesting science study as well.

He added, “If we think it may have another explosive event, if seismicity is still high we might keep it at Red for a while, but it had dropped down to lower levels and it was essentially at background levels, so we wanted to reduce it down to orange.”

There is still much to learn about underwater volcanoes, as modern techniques for locating submarine volcanoes rely almost completely on sound.