In recent weeks, scientists in the Philippines had been intently watching the Taal volcano,
as it produced a third series of volcanic explosions.
Thus, because so much attention was given to Taal, we were quite surprised when another
nearby volcano erupted.
On November 30th, at 12:09 pm local time, an explosive eruption occurred at the famed
Mount Pinatubo volcano.
This eruption lasted for 4 minutes, and sent a plume of ash 14,300 meters or 44,000 feet
into the atmosphere.
While this occurred, Philippines AirAsia Captain Aljess Lasmarias snapped some from photos
from the cockpit.
Note how the ash plume is mostly white instead of the usual gray color large eruption plumes
are.
This indicates that very little ash is in this plume and that it is almost completely
water vapor.
Because of this surprise eruption, although there is not yet an official evacuation order,
I would recommend a 3 kilometer evacuation radius at this time.
So, what will happen next at Mount Pinatubo?
Will there be another caldera forming eruption, similar to what was experienced in 1991?
This video will answer these two questions and discuss this unexpected eruption.
Mount Pinatubo can be found on the island of Luzon in the central western Philippines.
Specifically, it is 90 kilometers northwest of Manila.
From satellite, Mount Pinatubo is quite easy to spot as there are a series of gray pyroclastic
flow and lahar deposits which radiate outwards from its summit.
These were emplaced during the 1991 eruption of Mount Pinatubo, which caused the 1,745
meter tall volcano to collapse downwards to a height of 1,486 meters, forming a 2.5 kilometer
wide caldera.
In total, this eruption ejected 13 cubic kilometers of volcanic rock, marking it as the largest
volcanic eruption in the Philippines of the last 5,000 years.
Pyroclastic flows from this eruption reached up to 16 kilometers distant, destroying everything
in their path.
This major eruption was only the latest of several large volume eruptions Pinatubo has
produced.
Pinatubo has a long-term eruptive cycle, which is important in order to understand the context
of the latest eruption.
First, a very long period of dormancy occurs, lasting between 500 and 3,000 years in length.
This dormancy is interrupted by a large explosive eruption, such as what occurred in 1991.
For a period of several hundred years following the major eruption, a combination of small
phreatic and lava dome forming eruptions occur at the volcano, thus largely filling in any
craters or calderas which once existed.
Since a caldera forming eruption occurred a mere 30 years ago, what was just witnessed
was one of the small phreatic eruptions to be expected in the period following a major
eruption.
Phreatic eruptions occur when underground magma slowly heats surrounding rock, causing
any nearby groundwater to flash to steam.
Eventually this steam becomes overpressurized and takes up more space than the rock containing
it, resulting in an explosive eruption.
The eruption which occurred today was purely phreatic, as it did not contain any small
fragments of lava, indicating that the source of magma which caused the eruption is still
quite deep.
In the next several days to weeks, more similarly sized phreatic eruptions should be expected,
meaning that the overall volcano should be closed off to the public for some time.
Although not truly a certainty, there is a slight possibility that the magma which triggered
this latest eruption could erupt into the caldera lake, and begin to build a new lava
dome.
However, the current level of volcanic earthquakes and sulfur dioxide gas is insufficient to
suggest an imminent magmatic eruption.
For those of you who are still worried about this volcano, here is some greater context.
One way to determine how much magma is present is based on the amount of sulfur dioxide gas
it emits.
Before the climax of the major eruption in 1991, these levels were more than 13,000 tons
per day.
In comparison, today levels of sulfur dioxide are a mere 341 tons per day right now.
While another explosive eruption is quite likely, a major eruption is not expected at
this time.
Thanks for watching.
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