LOS ANGELES, CA (Catholic Online) - The Merapi volcano in Indonesia killed 5,000 people in May of 2006. Ash from the Merapi was thrown into the sky as high as four miles. Geologists say the Merapi is capable of major eruptions, and the frequency of those eruptions is now every 10 to 15 years.

The Nyiragongo volcano in the Democratic Republic of the Congo blew its top in 2002, and lava flows are still going strong today. Since the sides of this volcano are steep, the lava flows have the ability to move quickly and sweep away people and livestock. When an eruption in 1977, Nyiragongo flooded 20 square kilometers in an hour and killed around 70 people. A 2002 eruption sent lava streaming out of fissures directly through the center of town, destroying 40 percent of its buildings, while killing dozens and displacing half a million people.

The Avachinsky volcano in Russia erupted in 1945 and gave a horrific demonstration of its potential destructive power. That eruption was categorized as a level 4 out of 8 on the Volcanic Explosivity Index. The Eyjafjallajokull eruption was also a level 4). Avachinsky is also classified as a "somma" volcano because its structure resembles that of Italy's Mount Vesuvius, whose eruption in 79 A.D. destroyed Pompeii.

The Santa Maria Volcano in the western highlands of Guatemala erupted in 1902, killing about 5,000 people. It was one of the four largest volcanic eruptions in the 20th century, registering a VEI magnitude of 6 and leaving a 700-by-1,000 meter crater behind. Survivors of the eruption later contracted malaria and died - scientists theorize that the eruption killed many of the birds who fed on the mosquitoes in the area. The Santa Maria remains active today.

The Taal volcano in the Philippines is near populated areas and poses an ongoing threat in the area. There have been 33 eruptions reported at the Taal since 1754. Travel around the area is restricted as it remains highly unstable. Its last big eruption in 1977 killed 100 people.

Finally, the Yellowstone Supervolcano in Wyoming has been inactive for many, many millennia, but there's no guarantee it will remain so. The volcano - and popular tourist attraction is capable of a VEI magnitude of 8. When that happened in Indonesia 70,000 years ago, the blast sent the world into a devastating volcanic winter that dramatically changed the course of human evolution. But there's no real reason for concern - just yet.