One of Iceland’s most active volcanoes, Bárðarbunga, shook the earth four times in recent weeks, an indication it’s getting ready for eruption. Since part of it sits under an ice cap, an eruption could impact areas beyond the island.
The earthquakes—measuring magnitudes of 3.9, 3.2, 4.7, and 4.7—are an ominous sign—pressure in the magma chamber below the volcano is likely building to a breaking point. Geologists warn that the volcano is poised to erupt, though they don’t know when it will happen or how significant it will be.
Despite Bárðarbunga’s remote location, the effects of its eruption could be felt well beyond Iceland. One-third of the system its a part of is covered by Europe’s largest ice cap, and volcanoes covered with ice can be highly explosive and produce lots of fine ash—which spews into the atmosphere and can affects larger areas. In 2010, when the Eyjafjallajökull volcano erupted, it threw ash miles into the atmosphere. For days, air travel throughout Europe ground to a halt—planes couldn’t risk flying through the engine-destroying ash cloud that stretched from Ireland to Russia.
Bárðarbunga poses similar risks. Here’s Elaina Zachos, reporting for National Geographic:
Eruptions under ice can trigger explosions by turning large volumes of ice into steam, and as magma hits the steam it explodes into fine particles that can shoot high into the atmosphere. Or, lava from an eruption could melt the ice and cause flooding, like that brought on by the Eyjafjallajökull eruption.
Bárðarbunga’s most recent explosion was from August 2014 through February 2015, and it was the largest the country had seen in 200 years. Pollution—especially fine particulate matter that can be hazardous to breathe—blanketed western Europe.
Iceland’s residents aren’t strangers to volcanic eruptions. On average, a volcano in the system erupts once every 50 years.