Several volcanoes are known for their large eruptions, which caused their summit to collapse
to the side. Two examples include Mount Saint Helens in 1980 and Mount Meru in 5850 BC. However,
neither of these volcanoes produced a landslide quite as large as the topic of this video.
The volcano I am referring to is called Mount Raung, which produced a massive landslide that
traveled 79 kilometers, almost reaching the Indian Ocean. Today, Raung is erupting once
again. This video will discuss this volcano, and mention what its future hazards are.
The Raung volcano is located in Indonesia where it is on the eastern edge of the
island of Java. This volcano is located 21 kilometers west southwest of another famous
volcano called Ijen which produces blue lava. Both Raung and Ijen are quite young volcanoes,
which were built on a massive caldera which formed through a very
large explosive eruption 50,000 years ago. The first documented eruption from Raung
occurred 38,000 years ago, when magma reached the surface on the western side of the caldera.
Over approximately ten thousand years, these eruptions built a volcanic cone called Suket.
After this volcanic cone became extinct, eruptive activity moved to what is now west northwest of
the modern summit. Over a span of more than ten thousand years, a new volcanic cone was
built out of a combination of gray andesitic lava and layers of ash. Eventually, this volcanic cone
stood at 2900 meters tall. Then, sometime in the last 20,000 years, the modern Raung volcano began
to form. For the first several thousand years, it erupted infrequently as the volcanic cone to the
west, called Gadung was the primary vent. However, as Raung became taller and taller, its edifice
began pushing Gadung slowly to the west, causing high levels of structural instability. Eventually,
this pressure became too great, and Gadung almost completely collapsed in a massive landslide.
Over the span of several minutes, a fast landslide swept downhill to the west of Gadung.
It continued onwards and onwards, until it almost reached the Indian Ocean. In total,
this landslide covered 1045 square kilometers of land with an average thickness of 24 meters
of rock. Debris from this landslide traveled up to 79 kilometers, and had a total volume of 25 cubic
kilometers. Along the way, this landslide created numerous rounded hills called Hummocks. These
hummocks can be seen throughout eastern Java, indicating other large collapses in the region.
As a result of this landslide, the volcano was reduced to a height of 1700 meters. Afterwards,
a lava dome grew out of the collapse scar. After this lava dome stopped erupting,
volcanic activity continued exclusively at Raung. By 5,000 years ago, this volcano had grown to
3400 meters tall. So, why is Raung several hundred meters shorter today? The answer is that
the volcano suffered a recent catastrophic VEI 6 eruption, although we aren't exactly sure when
this occurred. This eruption reduced the overall height of Raung, and formed a 2 kilometer wide
caldera. Today, this caldera has a prominent steep 300 meter tall rim, and its center is overlaid
with recent flows of lava. Written records of this volcano's eruptions go back to 1586,
since which 73 different eruptions have occurred. All of these eruptions were explosive in nature,
although a few of these stand out. The largest eruption since records have been kept occurred
in 1593, which ejected a cubic kilometer of lava and ash which rained down in the
surrounding landscape. This eruption generated pyroclastic flows which escaped the caldera rim.
In 1638 and then again in 1817, large VEI 4 eruptions occurred, which created deadly
lahars as water swept away large volumes of ash. The current cinder cone in the summit caldera
formed in 1913, since which it has represented the main active vent from Raung. Today,
this cinder cone regularly emits bombs of lava in strombolian style mildly explosive eruptions.
On occasion, it produces larger explosions, leading to temporary suspension of all air traffic
in the region like what occurred in 2015. However, the main threat from this volcano is lahars.
Any time a large explosive eruption occurs, be careful during the next rainstorm.
These storms will wash away large volumes of ash, creating unusually large flash floods
called lahars. These lahars have historically most impacted towns to the southeast of Raung.
If you live in these towns and a large eruption occurs, get away from any riverbeds.
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