Volcano specialists warned on Tuesday that the earthquake-stricken island of Sao Jorge in Portugal’s Azores archipelago might see an early eruption comparable to Spain’s La Palma last year, which destroyed thousands of buildings and crops over an 85-day period.

More than 20,000 minor earthquakes have shook the lush mid-Atlantic island in the last 11 days, with the largest tremor since the start of the “seismic crisis” recorded on Tuesday evening with a magnitude of 3.8, according to the region’s CIVISA seismo-volcanic observation center.

The earthquake had a magnitude of 4 according to Portugal’s meteorological office, IPMA. There are worries that the tremors, which have so far caused little damage, might foreshadow a volcanic eruption, or a severe earthquake, for the first time since 1808. The tremor on Tuesday was felt in Sao Jorge as well as in the nearby volcanic islands of Terceira, Pico, and Faial.