Fire-spewing mountains

The highest warning level, red, has been declared for the Bardarbunga volcano in Iceland. The volcano is nearly invisible, hidden well beneath the Vatnajokull glacier. The weather office says nearly 2,500 earthquakes have been registered in the last few days. Signs of magma movement have also been detected.

Four years ago, the eruption of Icelandic volcano Eyjafjallajökull disrupted European air traffic for six days. More than 10 million air travelers were affected, and the disruption resulted in $1.7 billion ( 1.3 billion euros) in lost business. Bardarbunga is even larger than Eyjafjallajökull and would release much more magma during an eruption.

Worldwide there are at least 500 to 600 active volcanoes. Every year about 50 of them erupt. Volcanic eruptions are fascinating as natural phenomena, but when humans are endangered, things can quickly turn catastrophic. Huge lava streams and pyroclastic flows can engulf entire villages without warning.

Shorty after such a violent explosion, however, life returns. First, plants regrow and people return to rebuild their destroyed towns at the foot of the volcano. They do so despite the danger, because they know that volcanic ash makes for very fertile soil and thus good harvests. It is rich in phosphorus, potassium and calcium.

With an area of around 103,000 square kilometers (40,000 square miles) and about 30 active volcanoes, Iceland is considered the largest volcanic island in the world. Eyjafjallajökull in April 2010 and Grímsvötn in May 2011 are two of the most famous eruptions. The record-breaking volcanoes are, however, not in Iceland.

Kilauea in Hawaii is the most active volcano on earth. It releases the most magma but is normally not explosive. The name of the volcano in the Hawaiian language therefore means "spitting" or "lots of spreading." Lava isn't released explosively, but springs forth from the earth's interior and is released in lavaflows. On January 3, 1983, an eruption began that has persisted until this day.

The largest volcano is also found in Hawaii: Mauna Loa. It is 4169 meters tall (13,700 feet), and, when measured from sea level, it is one of the tallest mountains in the world. Measured from the ocean floor, its actual height is about 10,000 meters (32,800 feet). Mauna Loa last erupted on March 25, 1984 and is currently dormant.

In explosive contrast, Izu-Oshima in Japan erupted in 1986, releasing a 1600-meter-high lava fountain, the tallest ever recorded.