Deafening explosions of hot gas rattled evacuees miles (kilometers) from an Indonesian volcano Monday, the latest eruption in a deadly week. The country reported increased rumblings at 21 other active mountains, raising questions about what's causing the uptick along some of the world's most prolific fault lines.

No new casualties were reported in Mount Merapi's new blast, which came as Indonesia also struggles to respond to an earthquake-generated tsunami that devastated a remote chain of islands. The two disasters unfolding on opposite ends of country have killed nearly 500 people and strained the government's emergency response network. In both events, the military has been called in to help.

Merapi has killed 38 people since it started erupting a week ago. Monitoring officials have also raised alert levels at some of the 129 active volcanoes in Indonesia, with two under watch for possible eruption within two weeks and 19 showing increased activity - more than double the usual number on the watch list, an official said.

Indonesia, a vast archipelago of 235 million people, is prone to earthquakes and volcanos because it sits along the Pacific "Ring of Fire," a horseshoe-shaped string of faults that lines the western and eastern Pacific. Scientists could not say for certain what was causing the increased volcanic activity, though two theorized the earth's tectonic plates could be realigning and one noted growing evidence that volcanos can affect one other. [ MYWAY NEWS ]