Mount Merapi is once again producing a series of large pyroclastic flows which are making
the news.
The pyroclastic flow shown here traveled about 3 kilometers from its summit.
However, this isn't too unusual, as the volcano has been almost continuously erupting since
1548.
This video will discuss this active volcano in Indonesia, and mention what its future
hazards are.
Mount Merapi can be found in the central part of the island of Java.
Specifically, it is 56 kilometers south of Semarang.
This volcano exists due the subdduction of the Australian tectonic plate underneath the
Sunda plate.
The Australian plate is denser than the crust of the Sunda plate, so it is forced downward.
The oceanic crust from this tectonic plate then melts and migrates upwards until it erupts
on the surface, creating a volcano.
Mount Merapi began forming 138,000 years ago, when a series of eruptions created the Turgo
hill.
The eruptions at this hill were largely effusive in nature and likely produced tall lava fountains.
3,000 years later, another volcanic hill formed a kilometer to the east which was called Plawangan.
The next period of volcanic activity began around 109,000 years ago, and created Mount
Bibi.
The eruptions from Mount Bibi were slightly more explosive in nature than those which
occurred during the previous period.
Lavas from this volcano slowly built a stratovolcano which a wide 8 kilometer base.
The subsequent period of volcanic activity began 30,000 years ago, and formed a new volcanic
cone on top of the lavas from Mount Bibi.
This volcanic cone was referred to as Old Merapi.
For the next 22,000 years, this cone represented the summit of Mount Merapi.
This changed when the summit was destroyed in one or more massive debris avalances, which
caused a portion of this mountain to slide to the southwest.
The mechanism of these events was likely similar to the 1980 eruption of Mount Saint helens
in the United States.
The final period of volcanic activity began 6700 years ago and continues to the present
day.
This period has featured more than 100 distinct eruptions of primarily andesite lava.
These eruptions helped to create a now 2910 meter tall mountain.
Eruptions from this modern volcanic edifice are often highly explosive in nature.
One of the largest eruptions to occur from this mountain in the last several thousand
years took place in 1180 BC.
This eruption produced at least 100 million cubic meters of ash and tephra.
Over the past several hundred years, eruptions at Merapi have followed a predictable pattern.
Initially, an eruption produces lava near the summit of the mountain.
This lava then slowly builds up over time, forming a plug which blocks the main summit
crater.
Hot gasses and additional magma get trapped underneath, which build up in pressure.
Once the pressure reaches a certain point, these gasses and lava are forced out of the
volcano in a large explosion.
These explosions and the associated dome collapses are the cause of the frequent and deadly pyroclastic
flows at this volcano.
To understand the extreme extent of hazards from Mount Merapi, let me remind you of a
recent large eruption, which occurred in 2010.
During this eruption, the volcano produced a long distance pyroclastic flow which traveled
13 kilometers from its summit.
The eruption also produced bombs of lava, lahars, AND caused 30 centimeters of ash to
fall on a village 15 kilometers away from the mountain.
Although most eruptions are 1 or 2 orders of magnitude smaller than the 2010 eruption,
there is still an extreme danger posed by their effects.
For example, pyroclastic flows which travel a kilometer or more occur several times a
year.
These are essentially impossible to predict in the short term during eruptions, which
puts the lives of everyone who remains nearby in jeopardy.
I personally would recommend a permanant 5 kilometer exclusion zone around the mountain,
which increases to 15 kilometers towards the southwest of the summit.
However, 49,000 people live within 5 kilometers of Merapi.
Moving large numbers of people is not an easy task, but perhaps showing them the scientific
data might work.
For example, this map shows where pyroclastic flows reached between 1911 and 2006.
I hope that you enjoyed this video.
If you would like to request a specific topic, please leave a comment below.