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We have previously looked at volcanic lakes and have understood that they pose certain unforseen roles, especially if the volcanism in the area is not well understood. Today we will look at another type of volcanic related lake: the lava lake.
Usually the focus of very pretty photographs or extremely cool eruption videos, the dangers that lava lakes pose is not often talked about. When discussing the hazards associated with these lava lakes, it is usually related to something along the lines of: "don't go near" and "don't fall in." These lava lakes tend to be confined within craters of volcanoes, and as such, direct hazards associated with these lakes are confined to being in close proximity with the lava lake. Hazards related to these lava lakes, such as at Ambrym, Vanuatu, or Kilauea, Hawai`i, tend to be hazards from eruptive activity, such as ejection of materials (bombs, ash, etc.), or the emissions of poisonous volcanic gas, like sulphur dioxide. But did you know, that if conditions are just right, a lava lake can be dangerous to areas surrounding and away from the volcano?
Nyiragongo volcano, located in the Democratic Republic of Congo, has been a rather active volcano. Unfortunately, due to much political unrest in the area, Nyiragongo is not as well studied by scientists as they would like. Twice in recent history, Nyiragongo has had two devastating volcanic eruptions, the first related to the lava lake, while the second from a deadly eruption off the flank of the volcano. Nyiragongo's lava lake is found at a maximum elevation of 3250m (pre-disaster), inside a 3465m tall stratovolcano; the lava lake has an estimated depth of 600m and contains one of the most fluid lavas on Earth. Usually, a lava flow from an erupting volcano does not pose as problematic as other dangerous hazards, as it does not travel as fast as pyroclastic flows, block and ash flows, or lahar flows. In comparison with these hazards, a lava flow generally moves much slower, on the order of 1 to 10 km/hr. During certain lava flow eruptions in Hawai`i, residents have been able to outwalk an oncoming lava flow*. The lava found in Nyiragongo's lava lake, however, is different, as it is much less viscouc, of highly alkaline composition, and is believed to be fed by a plume under the volcano. This means that it is super fluid and able to move up to speeds of 97 km/hr.
Figure above: Nyiragongo and its lava flows down the flanks (From http://oddstuffmagazine.com)
Video above: Slow lava flows in Hawai`i that destroy homes in Hawai`i.
Now you may be thinking, what is the issue here? This lava, as fluid as it may be, is inside the volcano in the lava lake. How did it cause such destruction on the communities around Nyiragongo? The thing to remember is that there are 3 factors in this problem:
1. The lava is super fluid and can move fast.
2. The lava lake is rather deep, meaning there is a large volume of this lava available.
3. The lava lake is perched at the top of a very tall and steep sided stratovolcano.
On the 10th of January, 1977, the crater wall holding the lava lake ruptured. (The exact reason this happened has not yet been well understood, and this is why Nyiragongo still needs to be studied, to predict if this can happen again.) Within 30 mins, the entire lava lake had drained, sending an estimated 3 to 5 million cubic meters of lava to the north, west, and south of Nyiragongo. These lava flows reached up to 100 km/hr, wiping out several of the surrounding villages and burning almost 300 people alive. Reports from eye witnesses stated that the lava flows reached the outskirts of the nearest large city, Goma, within 20 mins. The only lucky thing about this event was that most of the lava drained out was directed into the surrounding forests. The destruction could have been worse if the direction of the flow had been elsewhere.
Figures above: Destruction of the draining of the lava lake in 1977 (Photos by M. Kraft)
Volcanoes can be considered dangerous because of the hazards they pose. But what makes Nyiragongo one of the most dangerous volcanoes in the world is that, aside from the danger of super fast lava flows that drain into nearby cities, the reason for why this happened is not well known, and the inability of scientists to predict such lava lake draining events is not yet possible. Attempting to climb the volcano is also dangerous, as the crater walls could rupture any time.
Video above: A look at Nyiragongo's lava lake
As it turns out, lava lakes can be pretty deadly, and at Nyiragongo, it makes it one of the most dangerous volcanoes in the world. Next time you see a video of a pretty lava lake, don't forget the dangers that lurk behind the mesmerizing, swirling pool of lava.
* Warning: VolcanoWorld does not in any way suggest that you try to outwalk a lava flow. If there is certain danger in the area, please follow evacuation directions as given by officials and STAY SAFE.
For a cool account of National Geographic visiting Nyiragongo's lava lake and trying to study it, check here.
For more information on Nyiragongo, check here.