Two strong earthquakes hit one of Iceland's largest volcanoes on Monday morning, and scientists are monitoring for an eruption, which would be its first in 98 years.
A 2010 eruption at another Icelandic volcano produced a giant ash cloud that shut down much of Europe's airspace. Airlines canceled 17,000 flights, and lost millions of dollars.
The Katla volcano shook in two separate events on Monday, measuring magnitudes 4.6 and 4.5, according to the Icelandic Meteorological Office.
There are no indications of an eruption, but Icelandic scientists are watching the volcano, according to Icelandic news organization Iceland Review.
Although Katla has not erupted since 1918, the Icelandic Meteorological Office considers it one of the country's most active volcanoes. The Catalogue of Icelandic Volcanoes says Katla has erupted 21 times in the last 1,100 years, and 18 have broken through the massive ice cap that sits in the volcano's central crater.
Small earthquakes at the volcano are common, especially in summer, the meteorologic office said. The office released a report in July saying 100 shallow earthquakes had already happened this past summer, four times the monthly average.
"In recent weeks, it seemed that the summertime unrest was abating," the office said in a statement sent to CNBC, "however today's seismicity marks a further escalation that stands out in comparison with seismic activity in the area in recent decades."
These two earthquakes are the strongest tremors to hit the volcano since the late 1970s, the Iceland Review noted. Katla is 90 miles east of the capital, Reykjavik.
The country's most active volcano, Grímsvoetn, erupted in 2011.