Indonesia’s Mount Sinabung has now released a plume of ash strong enough to cover the provincial capital of North Sumatra.

The residents of Medan now have to don masks to be able to breathe when they step outside of their homes or businesses.  The city is located 31 miles from the volcano and has a population of 3.4 million people.

The monitoring post watching the mountain says seven hot ash avalanches slid down the mountain on Wednesday for a distance of 10,500 feet.  The ash cloud from the eruptions rose over a mile into the sky.

Mount Sinabung, located on the Pacific Ring of Fire, had been dormant for 400 years before roaring to life in 2010.  Scientists who are investigating the rebirth of dormant volcanoes have published a study suggesting that earthquakes could be the cause.

Solid Earth, the journal of the European Geosciences Union, suggests that “megathrust earthquakes” in the region around previously dormant volcanoes could be the cause of new eruptions.  In the case of Mount Sinabung, three megathrust quakes between 2005 and 2007 could have sparked the volcano’s 2010 awakening. These earthquakes include the magnitude 8.6 earthquake in 2005, the magnitude 7.9 earthquake in 2007, and another magnitude 8.4 earthquake in 2007.