Iceland was rocked by the largest earthquakes in 39 years, prompting fears its largest volcano will erupt after almost a century of dormancy.

Two quakes -- of magnitudes 4.5 at 1:41 a.m. and 4.6 at 1:47 a.m. Monday- rocked the crater of south Iceland's Katla in the Myrdalsjokull glacier, the Icelandic Meteorological Office reported. They are the largest quakes to hit Katla since 1977, when a 5.1 earthquake was measured there, according to the Iceland Review.

Katla, which is 90 miles east of Reykjavik. has not erupted since 1918, when it lasted 24 days and caused major glacier river floods. But the office considers it one of the country's most active volcanoes. Katla has erupted 21 times in the last 1,100 years, and 18 broke through the ice cap in the volcano's central crater, according to the Catalog of Icelandic Volcanoes.

Icelandic scientists are watching the volcano, according to Icelandic Meteorological Office.

On July 29, the office reported, "Around Katla we are not detecting signs of increased ground deformation or bursts of seismic tremor, which are both signals that might indicate movement of magma," the agency said. "We continue to monitor Katla closely and will issue updates. ... Our assessment is that the volcano is in a period of summertime unrest and it does not show signs of impending eruption, although we cannot rule out a sudden escalation in seismicity in connection with a hazardous flood."

In 2010, another Icelandic volcano, Eyjafjallajökull, produced a giant ash cloud that forced airlines to divert thousands of flights in Europe.

(UPI)