Indonesia is the most active volcanic area on Earth, with 129 active volcanoes. Located straddling the equator and the Ring Of Fire, the country is a long string on islands, who owe their existence in many cases to a volcanic eruption at some time in the past. A glance at the news at any given time could easily speak of the latest volcanic eruption in the country. In recent weeks Mt. Kelud in East Java has gestured that its ready to erupt, villagers having to be forcibly removed from their land. In Sulawesi Mt. Soputan erupted on October 25th, creating smoke and ask, but no casualties.
A volcano is an opening, or rupture, in a planet’s surface or crust, which allows hot, molten rock, ash and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.
Volcanoes are generally found where tectonic plates pull apart or come together. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by “divergent tectonic plates” pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by “convergent tectonic plates” coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth’s crust.
There are many kinds of volcanoes and Indonesia possesses some of the most impressive, including Gunung Agung, Gunung Rinjani and Mt. Bromo in East Java.
Stratovolcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as composite volcanoes. Strato/composite volcanoes are made of cinders, ash and lava. The volcanoes are made by a another volcano. Cinders and ash pile on top of each other, then lava flows on top and dries and then the process begins again. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy.
Supervolcano is the popular term for a large volcano that usually has a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park of western USA and Lake Taupo in New Zealand. Indonesia also has the largest super volcano in the world, Lake Toba.
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Indonesia’s most active volcano is Mt. Merapi in Central Java. Merapi is the youngest in a group of volcanoes in the area and is situated at a subduction zone, where the Indo-Australian Plate is sliding beneath the Eurasian Plate. Merapi has contributed to the history of the country. Typically, small eruptions occur every 2-3 years, and larger ones every 10-15 years or so. Notable eruptions, often causing many deaths, have occurred in 1006, 1786, 1822, 1872 the most violent eruption in recent history), and 1930—when thirteen villages were destroyed and 1400 people killed by pyroclastic flows.
Some of Indonesia’s more notorious volcanoes include:
• Agung, Bali
• Colo, Suluwesi
• Dieng, Java
• Galunggung, Java
• Gamalama, Halmahera
• Kelut, Java
• Krakatau, Sunda Strait
• Merapi, Java
• Papandayan, Java
• Semeru, Java
• Tambora, Sumbawa
The 1815 eruption of Tambora was the largest eruption in historic time. About 150 cubic kilometers of ash were erupted (about 150 times more than the 1980 eruption of Mount St. Helens). Ash fell as far as 800 miles (1,300 km) from the volcano. In central Java and Kalimantan, 550 miles (900 km) from the eruption, one centimeter of ash fell. The Volcanic Explosivity of the eruption was 7. The eruption column reached a height of about 28 miles (44 km). The collapse of the eruption column produced numerous pyroclastic flows. As these hot pyroclastic flows reached the ocean where they caused additional explosions. During these explosions, most of the fine-fraction of the ash was removed. The eruption formed a caldera. An estimated 92,000 people were killed by the eruption. About 10,000 direct deaths were caused by bomb impacts, tephra fall, and pyroclastic flows. An estimated 82,000 were killed indirectly by the eruption by starvation, disease, and hunger.
In Bali the 2 largest volcanoes are Gunung Agung and Gunung Batukaru. Gunung Batur in the Kintamani area is a complex of coalesced volcanic cones inside of two nested calderas. The calderas formed about 50,000 and 20,000 years ago, the larger being 13kms long. Agung is the most active volcano on Bali and last erupted in 1963, it is overdue for another eruption.
Hiking a volcano in Bali or in other parts of Indonesia can be an enjoyable experience. Batukaru can be hiked during the day starting behind the large temple at Pura Luhur Batukaru. Partially forested, this hike will take several hours to reach the summit and camping is possible. Gunung Agung can be hiked from behind Besakih temple, or from Pura Pasar Agung. The shortest route takes a few hours to get up and is hard on the knees. One of the most enjoyable hikes in Gunung Catur at Bedugal. This forested route is free to hike and should be done during the day. Gunung Batur is a spectacular sight, when viewed from the crater rim and you’ll have to pay spectacular prices to hike it.
[photo shows orbital shot of volcanoes in Central & Eastern Java.]