In January of 2022, the underwater volcano Hunga Tonga-Hunga Ha’apai
produced the biggest atmospheric explosion seen in modern history.
Scientists have had their eyes on this volcano ever since an eruption
in 2015 joined two islands together. This recent eruption blew that bridge apart,
inundating islands in Tonga with meters-high floods and a coat of ash and dust.
Detectors around the world picked up the
pressure wave from Hunga Tonga-Hunga Ha’apai–
people in Alaska could hear the blast,
and tsunami waves triggered an oil spill in Peru.
Scientists are still untangling all the ways the
eruption rippled through the earth, ocean, and atmosphere.
Using a network of instruments:
from micro barometers to hydrophones and seismometers,
researchers characterized the impact of the eruption.
The main eruption resulted in shaking similar to a magnitude 5.8 earthquake.
Sound waves in various frequencies, from audible sound to infrasound,
below what humans can hear, reverberated around the world.
One type of pressure wave that disturbed the atmosphere, called a “lamb wave”,
circled the Earth six times in four days.
This is similar to what was observed from one of the
deadliest volcanic eruptions in recorded history–
the 1883 eruption of Krakatoa, Indonesia.
Like Tonga, the 1883 eruption also triggered tsunamis around the world.
Researchers suspected interactions between the atmosphere and ocean
could have triggered the lamb wave,
but didn’t have the data to back it up.
Then came the Tonga eruption:
a perfect opportunity for scientists to understand these tsunamis
using modern day sensors.
Most tsunamis we see are “ordinary” tsunamis.
Disturbances like earthquakes or landslides
move large amounts of water, creating waves.
Waves caused by the displacement of water near the volcano
moved throughout the Pacific ocean,
and tsunami warning systems accurately predicted when they would arrive.
But another kind of tsunami–a driven tsunami–
eluded warning systems, arriving two hours before these “ordinary” waves.
A pressure wave rippling through the atmosphere
was strong enough to move water, creating “driven” waves that were small,
but traveled all around the world.
These different types of waves from the eruption meant the Tonga tsunami
lasted longer than earthquake-induced tsunamis.
In addition to waves moving across the world,
the eruption shot a giant plume of water vapor and gas into the sky.
At its peak, the plume reached 57 kilometers high.
That’s more than triple the height of a commercial flight,
and the tallest ever measured by a satellite.
Most volcanic plumes deposit lots of ash, dust and
sulfur dioxide into the troposphere,
but only the most energetic ones penetrate higher into the upper atmosphere.
These aerosols temporarily cool the earth by reflecting
solar radiation from the sun back to space.
But Tonga was unique–the significant amount of water in the plume
meant less sulfur dioxide–and a lot more water–
made its way into the stratosphere.
One set of researchers used data from weather balloons to measure
how much water vapor made it high into the sky.
They estimate that 50 million tons of water vapor
were spewed into the stratosphere–
equivalent to over 19,000 Olympic-size swimming pools.
That means water vapor in the stratosphere increased by at least 5%.
While the dust and sulfur dioxide reflect radiation,
the increased water vapor acts as a greenhouse gas that traps heat.
Water vapor also sticks around in the atmosphere longer than aerosols,
which means scientists are uncertain whether the eruption
will ultimately cool or heat the earth.
As researchers continue to analyze the treasure trove of data from the eruption,
they hope to create better warning systems and
models to anticipate the impact of future volcanic eruptions.