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A Sleeping or a Napping Giant?

Mount Agung’s New Found Calm May Signal Either a Return to Dormancy or a Coming Eruption

(12/3/2017) The head of the Central Agency for the Mitigation of Geological Disasters (PVMBG), Devy Kamil Syahbana, says the Mount Agung Volcano has suddenly become quieter as compared to its recent period of intensified seismic activity.

As reported by Metrobali.com, Devy said the newfound calm might mean that the molten lava that has made its way from deep below the mountain to the surface of the crater has hardened and solidified. Explaining that once lava is exposed above ground to the atmosphere it will quickly cool and harden. Thus if lava resides for an extended period in the crater is will both thicken and harden over time.

“If (the lava) hardens its mobility also decreases,” explained Devy on Sunday, December 3, 2017, during an interview at the Mount Agung Observation Post at Rendang, Karangasem.

He went on to explain that the question has now become whether or not the upward march of the lava has slowed because the mountain has depleted its energy source or is the lava's pathway is only blocked momentarily by lava that has hardened into a crust.

Based on the recent experience of Mount Rinjani in Lombok, Devy related how, following an eruption of that volcano, he climbed to the peak to take lava samples. Saying: “I once climbed Rinjani to gather a lava sample a few hours – less than 24 hours - after an actual eruption. The lava had already begun to cool. How the lava cools depends on the surrounding atmosphere.”

Continuing to relate his experience with Mount Rinjani, based on the measurements of sulfur dioxide (SO2) found within the mountain’s lava he detected a dramatic decrease in that gas – amounting to a 20x reduction than the SO2 present during the eruption.

The reduction of SO2 can happen when the energy driving the eruption has dissipated or then the lava channels have somehow become blocked and can portend a coming eruption.

Measurement done at Mount Galeras in Mexico just below it erupted also showed reduced levels of SO2 at the mountain’s peak. Merpati in Central Java also showed reduced levels of SO2 in 2010 prior to a major eruption.