[Rockhounds] Scientists Unravel How the Tonga Volcano Caused Worldwide Tsunamis

[Kreigh Tomaszewski]

In August 1883, a mountainous island in Indonesia named Krakatau, or
Krakatoa, self-destructed. Episodic volcanic eruptions crescendoed in an
explosion that sent debris 80 kilometers high and smothered 800,000 square
kilometers of Earth’s surface in corrosive ash. As much of the island
blasted apart and splashed into the sea, a tsunami rose up and slammed into
the nearby islands of Java and Sumatra, causing most of the eruption’s
36,000 fatalities.

While Indonesia bore the brunt of the damage, the Krakatau eruption had
perplexing effects across the world. Somehow, small tsunamis lapped at the
shorelines of countries in both the Pacific and Atlantic oceans, even
though there didn’t appear to be any way Krakatau’s tsunami could have
leapfrogged from the Indian Ocean over continents and into other ocean
basins. Lacking any other explanation, scientists at the time blamed these
far-flung tsunamis on coincidentally timed earthquakes.

But geophysicists in subsequent decades kept puzzling over the data. A study
from 1955 <https://ui.adsabs.harvard.edu/abs/1955TrAGU..36...53E/abstract>,
for example, found that the distant tsunamis correlated with the arrival of
the pressure wave that propagated outward through the air from the
eruption. The study’s authors speculated that some sort of coupling had
taken place between this atmospheric disturbance and the water. Computer
simulations in 2003
<https://www.researchgate.net/publication/29630185_Simulation_of_the_trans-oceanic_tsunami_propagation_due_to_the_1883_Krakatau_volcanic_eruption>
further
supported this, showing that Krakatau’s main tsunami, even where it did
make its way through gaps in the continents to reach both the Pacific and
Atlantic oceans, lagged behind tiny tsunamis in places like Hawai‘i,
California and Alaska, which instead synced up with the faster pressure
wave from the blast. (A pressure wave whose frequency is in hearing range
is known as sound.)

To corroborate the speculative idea that volcanoes’ sound or pressure waves
could cause tsunamis, scientists needed to see another version of Krakatau
play out in real time in the modern era — an awkward wish, to be sure.

https://www.quantamagazine.org/scientists-unravel-how-the-tonga-volcano-caused-worldwide-tsunamis-20220413/