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Ring of Fire

26 Nov 10
Willman
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Unless you live in Alaska or along some parts of the west coast, it’s not likely that you spend much time staring up at volcanoes. In Bandung though, we can’t avoid them. The town is literally ringed by volcanoes and mountains.

Indonesia is one of the most volcanically active areas in the world, and the island of Java, where we live, has the largest number active volcanoes in Indonesia – 45, including Mt. Merapi some eight hours away from us. Merapi, which erupted this past October, has in fact erupted more than 80 times since 1000 BCE.

Fortunately for us, there is little volcanic activity nearby. But around us they sit, including a large one just to the north of our home.

The country of Indonesia is made up of more than 17,000 islands, the product of something called Plate Tectonics. While the older folks among us may not know of the theory, I’m teaching Elana U.S. social studies while we’re here, and I was quite surprised to find it mentioned in her 5th grade text book.

Tectonics was first theorized in the early 1900s by among others Alfred Wegener, who died while exploring Greenland’s ice cap in 1930, more than three decades before his theory became widely accepted. Like many great ideas in science, Wegener’s theory ran counter to the conventional wisdom of the time, so he was at best ignored, and often ridiculed. It wasn’t until the development of the concept of seafloor spreading in the late 1950s and early 1960s that the theory became a part of mainstream scientific thought.

According to my admittedly simplistic understanding of plate tectonics, the Earth’s crust is made up of about 11 large and five smaller plates that move in various directions relative to each other. These plates drag the continents along, sometimes at the fantastic speed (in geological time at least) of 100mm a year, though usually it’s much slower.

The margins of the plates interact with each other in three basic ways. Divergent plates – those moving away from each other – lead to what is called “seafloor spreading.” This process causes the formation of mid-ocean ridges and active areas of rifting on land. Perhaps the best known example is the famous Rift Valley of Africa.

Other plates are side slipping, meaning that they move almost parallel to each other. The most familiar side slipping fault in America is the San Andreas Fault in California. Plates typically don’t slide smoothly. Friction causes the plates to catch, and when they release it can cause an earthquake.

Finally, some plates are convergent, meaning they are moving toward each other. These create what are known as subduction zones – an area where one plate slips under the other. The upper plate can also catch and fold, creating mountain ranges such as the Andes in South America. Such zones can also form islands, as happened in Indonesia.

Just south of Indonesia is the Java Trench, where the Eurasian and Australian Plates collide. This trench is a subduction zone, where the Australian Plate slides under the Eurasian Plate. This movement led to the formation of the Indonesian islands, and it’s why there is so much volcanic activity here.

Bandung, at 750m (2460 feet) above sea level, sits in a basin formed by a ring of volcanoes and mountains. No one seems to know just how many are actually volcanoes, but you can’t miss them. The city is defined, in part, by craters.

Most of the volcanoes have been dormant for many years. The most recent eruption appears to have occurred in 1969.

Because so many volcanoes are nearby, it’s only natural to want to explore, so when the kids had a week off from school recently we did just that.

Tangkuban Perahu, which means up-turned boat in the Sundanese language, is an active volcano about 30km (18.6 miles) north of the city, which places it about 20km north of us. It is considered to be a stratovolcano, a type noted for its steep-sided symmetrical cones. Perhaps the most well-known stratovolcano is Mt. Fuji in Japan. Tangkuban though doesn’t look quite like that. Its crater long ago collapsed into the mountain, giving it a flat top, which led to the local legend that says it is an overturned boat (the story is quite interesting, and a short version can be found on the mountain’s Wikipedia page).

The volcano is quite a tourist trap. Because a road leads right up to the main crater, and it is so close to town, the volcano is almost impossible to visit on the weekend. Some friends tried to take us there during one of our first weekends in town, and after a three hour drive spent mostly sitting still in traffic we gave up.

This time we were more successful, and after 45 minutes found ourselves staring into Kawah Ratu, the volcano’s main crater. There appear to be 11 or 12 craters in total. This particular crater is quite large. Unlike American tourist sites, where safety is a major concern, there is a short railing near the edge, but nothing else to prevent anyone from sliding down to the acidic lake below.

The crater is surrounded by a hiking trail, so we set off to try and walk all the way around, a trip said to take about two hours. But we were quickly stopped by the large number of people trying to sell us just about every type of tacky tourist gift imaginable, from little heads made out of coconuts to “eggs” made from nearby petrified wood. The huts lining the trail for a couple of hundred feet reminded me very much of the traders in the Andes of Bolivia. I guess trinkets are the same just about anywhere in the world. Of course, it didn’t help that nearby someone was playing a reed flute with music similar to that also found in the Andes.

After finally dodging the sales pitches, we continued along the trail until we reached a barricade blocking our path. As it turns out, the sulfur gas being released from the crater often blows to the north, creating what is known as Death Valley. Even tourists are not expendable I suppose, so we were forced to turn back after stopping off at the “Holy Spring,” where water collects in a pool but there is no information to indicate why this spring might indeed be holy.

Back at the parking lot we visited a one-room “museum” about the volcano. It did not take long to realize that little real information was available, so we went back outside. About this time, the afternoon rains began, slowly at first, but after reaching the car it became a downpour. It was time to call it a day.

It was only while researching this post that I found the most interesting information of all. Twice in less than the past 20 years, the area around the volcano has been closed. That’s because seismologists were concerned about activity under the volcano, activity that may have indicated an eruption was imminent. No one mentioned that while we were visiting. And no one mentioned the possibility of an eruption when we rented our home, which sits on lava flows from past eruptions of this same volcano. In Indonesia, eruptions apparently don’t move people the way they do in the U.S.

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