On October 25, 2010, the Merapi Mount of Indonesia erupted three times, spewing lava down its southern and southeastern slopes. The eruption took casualties, and still Scientists have warned that pressure building beneath Mount Merapi’s lava dome could trigger its most powerful eruption in years.

But what is a volcano?

A volcano is a landform (usually a mountain) where molten rock erupts through the surface of the planet.

In simple terms a volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. It is a hole in the Earth from which molten rock and gas erupt.

The name “volcano” has its origin from the name of Vulcan, a god of fire in Roman mythology.

As pressure in the molten rock builds up it needs to escape somewhere. So it forces its way up “fissures” which are narrow cracks in the earths crust. Once the magma (the liquid rock inside a volcano) erupts through the earth’s surface it’s called lava (the liquid rock that flows out of a volcano). Fresh lava ranges from 1,300° to 2,200° F (700° to 1,200° C) in temperature and glows red hot to white hot as it flows.

There are around 1510 ‘active’ volcanoes in the world. We currently know of 80 or more which are under the oceans. Over half of the world’s volcanoes arise in a belt around the Pacific Ocean called the Ring of Fire (About 90% of the world’s earthquakes and 80% of the world’s largest earthquakes occur along the Ring of Fire!)

Zooming in on our neighbour country, Indonesia, we can see that the country mainly lies on active volcanoes.

The two most active volcanoes are the Merapi and Kelut volcanoes. Since the year 1000 AD, both have erupted more than 80 and 30 times respectively.

There are six known supervolcanoes in the world: 

1. the Yellowstone (United States)
2. Long Valley (United States)
3. Valles Caldera (United States)
4. Lake Toba (Indonesia)
5. Taupo Volcano (New Zealand)
6. Aira Caldera (Japan)

Supervolcanic eruptions typically cover huge areas with lava and volcanic ash and cause a long-lasting change to weather.

Volcanic Eruption Index (VEI) records how much volcanic material (ejecta) is thrown out, how high the eruption goes, and how long it lasts. The scale goes from 0 to 8. An increase of 1 indicates a 10 times more powerful eruption.

The largest known supervolcanic eruption known to date is the Toba eruption (VEI 8) 74000 years ago, throwing the earth into 6 years of volcanic winter and nearly putting human population to extinction, and was deemed responsible for slowing down the rate of human evolution. A more recent supervolcanic eruption, but to a much lesser scale is the mount Tambora eruption (VEI 7), also in Indonesia, in 1815, with ejecta volume of about 100-kilometer cubes.

(Picture: Toba Lake has not been active since the super-eruption, and now is a popular tourist destination in Indonesia)