Describing the devastating eruption in Tonga
Date:
March 29, 2022
Source:
University of California - Santa Barbara
Summary:
On January 15, the volcano Hunga Tonga-Hunga Ha'apai devastated
the nation of Tonga. The eruption triggered tsunamis as far afield
as the Caribbean and generated atmospheric waves that travelled
around the globe several times. Meanwhile, the volcano's plume
shot gas and ash through the stratosphere into the lower mesosphere.
FULL STORY ==========================================================================
On January 15, the volcano Hunga Tonga-Hunga Ha'apai devastated the
nation of Tonga. The eruption triggered tsunamis as far afield as the
Caribbean and generated atmospheric waves that travelled around the
globe several times.
Meanwhile, the volcano's plume shot gas and ash through the stratosphere
into the lower mesosphere.
==========================================================================
Just two months after the eruption, geologists have put together a
preliminary account of how it unfolded. UC Santa Barbara's Melissa Scruggs
and emeritus Professor Frank Spera were part of an international team of researchers that published the first holistic account of the event in the journal Earthquake Research Advances. The authors think that an eruption
the day before may have primed the volcano for the violent explosion
by sinking its main vent below the ocean's surface. This enabled molten
rock to vaporize a large volume of seawater, intensifying the volcanic
eruption the very next day.
"This is definitely, without a doubt, the largest eruption since
Mt. Pinatubo in 1991," said corresponding author Scruggs, who studies
magma mixing and eruption triggering mechanisms, and recently completed
her doctorate at UC Santa Barbara. She compared January's event to the
1883 eruption of Krakatoa, which was heard 3,000 miles away.
Hunga Tonga-Hunga Ha'apai (HTHH) is a stratovolcano: a large, cone-shaped mountain that is prone to periodic violent eruptions, but which usually experiences milder activity. It's one of many along the Tofua Volcanic
Arc, a line of volcanoes fed by magma from the Pacific Plate diving
beneath the Indo- Australian Plate. Heat and pressure cook the rocks of
the descending plate, driving out water and other volatiles. That same
water decreases the melting temperature of the rock above, leading to
a chain of volcanoes about 100 kilometers from the plate boundary.
A submerged danger The islands of Hunga Tonga and Hunga Ha'apai --
after which the volcano is named -- are merely the two highest points
along the rim of the caldera, or central crater. Or they were, until
the eruption blew most of the islands sky high.
========================================================================== Scruggs first heard about the eruption as she scrolled through her Twitter
feed while getting ready for bed. "I saw a GIF of the satellite eruption,
and my heart just stopped," she said, pausing to find her words. She immediately knew that the event would cause massive devastation. "The
scariest part was that the entire country was cut off, and we didn't
know what had happened." She was already messaging other volcanologists
as the events unfolded, trying to understand the images that satellites
had so clearly captured. "We really just set out to try to understand
what happened," Scruggs said. "So, we gathered all the information that
we could, anything that was available within the first few weeks." The
authors drew on whatever resources they could find to quickly characterize
this eruption, including publicly available data, videos and even tweets.
Using a variety of data sets, the team calculated that the January 15
event began at 5:02 p.m. local time (0402 +/-1 UTC). The U.S. Geological
Survey recorded a seismic event around 13 minutes later at the vent
location. The first two hours of the eruption were particularly violent,
with activity fading after about 12 hours.
But eruption activity had actually started all the way back on December
20, 2021. And before that, the volcano had erupted in 2009 and again
in 2014 and 2015. Scruggs believes these earlier episodes are key to understanding the violence behind HTHH's recent eruption, perhaps related
to changes in the magma plumbing system at depth or the chemistry of
the magma over time.
Hunga Tonga and Hunga Ha'apai used to be separate islands until they
were united by eruptions from the volcano's main vent, which created a
land bridge.
"This island was just born in 2015," said Scruggs. "And now it's
gone. Were it not for the satellite era, we would not have even known
it ever existed." On January 14, 2022 an explosion from the main vent
razed this connection, sinking the vent beneath the ocean's surface. "Had
that land bridge not been taken out, the January 15 eruption might have
behaved just like the day before because it would not have had that
excess seawater," Scruggs remarked.
==========================================================================
A staggering explosion Same volcano, one day's difference: On Friday
the vent was above the water, and by Saturday it was below. "That made
all of the difference in the world," Scruggs said.
The team believes that the seawater played a large part in the violence
and force behind the Jan. 15 eruption. Much like a bottle rocket, an
eruption of this scale takes the right ratio of water and gas to provide
the force to send it skyward.
And it took off like a rocket, too. "It went halfway to space," Scruggs exclaimed. The ash plume shot 58 kilometers into the atmosphere, past
the stratosphere and into the lower mesosphere. This is more than twice
the height reached by the plume from Mt. Saint Helens in 1980. It was
the tallest volcanic plume ever recorded.
A truly staggering amount of lightning also accompanied the eruption. The authors suspect that vaporizing seawater caused the lava to fragment into microscopic ash particles, which were joined by tiny ice crystals once
the steam froze in the upper atmosphere. The motion, temperature change
and size of the particles generated incredible amounts of static charge separation that flashed above the eruption. For the first two hours of
the eruption, about 80% of all lightning strikes on Earth split the sky
above Hunga Tonga-Hunga Ha'apai.
The authors estimate around 1.9 km3 of material, weighing 2,900 teragrams, erupted from HTHH on Jan. 15. "But the volume of the eruption was not
the big deal," said Spera, a coauthor on the paper and Scruggs' doctoral advisor. "What was special is how the energy of the eruption coupled to
the atmosphere and oceans: A lot of the energy went into moving air and
water on a global scale." The shockwave traveling through the ocean
triggered tsunamis throughout the Pacific, and beyond. What's more,
the wave arrived faster than tsunami warning models predicted because
the models aren't calibrated for volcanic eruptions - - they're based
on equations that describe tsunamis generated by earthquakes.
A second tsunami followed the atmospheric pressure wave. This shockwave
even triggered a meteo-tsunami in the Caribbean, which has no direct
connection to the South Pacific. Scruggs called it unprecedented:
"Basically the whole ocean just kind of sloshed around for five days
after the eruption," she added.
Plenty of work to do Scientists are still piecing together what happened
at the volcano, so they have yet to develop a complete understanding
of the tsunami wave. However, it's an important task needed to
update tsunami travel forecast systems so they account for this type
of mechanism. Otherwise, warnings could be incorrect the next time a
volcano like HTHH erupts, potentially costing more lives.
Indeed, the event highlights the danger posed by unmonitored submarine volcanoes. Despite the devastation, the people of Tonga were relatively
well prepared for the Jan. 15 eruption. The government had issued warnings based on the previous day's activity, and the nation had plans in place
for eruptions and tsunamis.
HTHH has experienced similarly violent eruptions in the past. A recent
paper by researchers at the University of Otago, New Zealand revealed
that a large eruption destroyed the caldera at the summit of the undersea volcano about 1,000 years ago. And similar volcanoes could well erupt
in the same manner.
Consider Kick 'em Jenny, another submarine volcano whose main vent is a
mere 150 meters underwater. It's located just 8 km north of the island
of Grenada.
"Imagine if something like the Tonga eruption happened in the Caribbean," Scruggs said.
The researchers worked quickly with only publicly available data. They
plan to revisit all their findings as more information and samples
become available and as more researchers publish their own findings on
this groundbreaking eruption.
Their primary goal was to provide a point of departure for future work
on the topic.
Scruggs is particularly keen on learning about the ash collected from
this eruption. Volcanic rock provides a wealth of information to a
trained geologist. Examining the material could shed light on the type
of magma that erupted, how much of it there was and perhaps even how
much seawater was involved in the eruption.
"There's so many questions that have been raised," said Scruggs. "Things
we didn't even think were possible have now been recorded." The UC Santa Barbara researchers will lead a special invited session on the Hunga Tonga-Hunga Ha'apai eruption at the Geological Society of America's 2022
annual meeting in Denver this October. "It will be exciting to see what
scores of other earth scientists can discover about this unique volcano,"
Spera said.
"We are just at the beginning."
========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Barbara. Original written by Harrison
Tasoff. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. David A. Yuen, Melissa A. Scruggs, Frank J. Spera, Yingcai Zheng,
Hao Hu,
Stephen R. McNutt, Glenn Thompson, Kyle Mandli, Barry R. Keller,
Songqiao Shawn Wei, Zhigang Peng, Zili Zhou, Francesco Mulargia,
Yuichiro Tanioka.
Under the Surface: Pressure-Induced Planetary-Scale Waves, Volcanic
Lightning, and Gaseous Clouds Caused by the Submarine Eruption of
Hunga Tonga-Hunga Ha'apai Volcano Provide an Excellent Research
Opportunity.
Earthquake Research Advances, 2022; 100134 DOI: 10.1016/
j.eqrea.2022.100134 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220329142523.htm
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