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Journal of Earth Science, Vo l. 33 , No. 2, p. 229–235, April 2022 ISSN 1674-487X
Printed in China
https://doi.org/10.1007/s12583-022-1624-2
Kusky Timothy M., 2022. Déjà vu: Might Future Eruptions of Hunga Tonga-Hunga Ha’apai Volcano be a Repeat of the Devastating
Eruption of Santorini, Greece (1650 BC)?. Journal of Earth Science, 33(2): 229–235. https://doi.org/10.1007/s12583-022-1624-2.
http://en.earth-science.net
Editorial
Déjà vu: Might Future Eruptions of Hunga Tonga-Hunga
Ha’apai Volcano be a Repeat of the Devastating Eruption of
Santorini, Greece (1650 BC)?
Timothy M. Kusky
Center for Global Tectonics, Three Gorges Research Center for Geo-Hazards, China University of Geosciences, Wuhan 430074, China
Timothy M. Kusky: https://orcid.org/0000-0002-4553-620X
The remote Pacific islands nation of Tonga (about 170 is-
lands, with a population of 105 000), and surrounding countries,
are suffering from the damage from one of the largest, most ex-
plosive volcanic eruptions in at least several decades, at least
since the 1991 eruption of Pinatubo in the Philippines. The data
is still coming in from the Jan. 15, 2022 eruption. Initial reports
show (remarkably) few casualties, but the islands are still (as of
this writing) inaccessible because of thick volcanic ash cover-
ings, loss of communication networks, and damage to the main
airport. Initial reports are optimistic, but the observations and
data are sparse. Tonga needs help, immediately.
Tonga is located in the northern part of the Tonga-Kermadec
subduction system, that extends for about 2 550 km between
New Zealand and Tonga. It has the deepest trench in the southern
hemisphere, and the second deepest in the world. The conver-
gence rate between the Pacific Plate on the east and the Tonga-
Kermadec arc to the west is about 15 cm/year (some estimates
in the far north suggest it may be 24 cm/year), showing that this
trench records the fastest plate velocities on Earth (e.g., van de
Lagemaat et al., 2018), which certainly contributes to its long
history of earthquakes, volcanic eruptions and tsunami. The back
arc side of the Tonga-Kermadec arc is extensional, forming a
complex back-arc basin system extending from the Lau Basin in
the north, to the Taupo volcanic zone in New Zealand in the
south (Fig. 1a, inset). The Hunga Tonga-Hunga Ha’apai volcano
(Figs. 1a, 1b, 1c) is located in the southern part of the Tonga
segment of the Tonga Kermadec arc (Plank et al., 2020; Cronin
et al., 2017), and before 2014, consisted of two andesitic islands
(Honga Tonga in the northeast and Hunga Ha’apai in the west;
Figs. 1b, 1c)), and have had notable eruptions before this phase
in 2014, 2009, 1988, 1937, and 1912 (Smithsonian Museum,
Global Volcanism Program, 2022; Bryan et al., 1972). The larg-
est part of the volcano is a giant submarine caldera, located to
the SE of the islands (Fig. 2). Some information suggests that
Hunga Tonga-Hunga Ha’apai has had catastrophic eruptions
similar in scale to the 2022 eruption about 1 000, and 2 000 years
*Corresponding author: tkusky@gmail.com
© China University of Geosciences (Wuhan) and Springer-Verlag
GmbH Germany, Part of Springer Nature 2022
Manuscript received January 19, 2022.
Manuscript accepted January 23, 2022.
ago, and the volcanic edifice was at times a huge volcano that
periodically collapses during these catastrophic events (Cronin,
2022; Cronin et al., 2017).
The Hunga Tonga-Hunga Ha’apai volcano is located about
30 km from Tonga’s island of Fonuafo’ou, and about 60 km from
the largest island, Tongatapu, with the capital, Nuku’alofa (Figs.
1, 2). The main eruption sequence started on Jan. 14, with a ma-
jor ash and steam eruption, accompanied by a magnitude 5.8
earthquake at 5 km depth (Global Alert and Disaster Coordina-
tion System, GDACS), accompanying the volcanic plume that
rapidly reached to more than 20 km in the atmosphere. The larg-
est eruption so far was on Saturday, Jan. 15.
The blast on Jan. 15 (5:10 a.m. Jan. 15 GMT; 6:10 p.m. lo-
cal time), after some days of major eruptions (Figs. 3, 4), started
with a magnitude 4.5 earthquake, and a sonic explosion that was,
remarkably, detected around the world, as the volcano possibly
collapsed underwater and the seawater rushed in, causing a huge
displacement of seawater. Residents of New Zealand, Australia,
and Alaska reported sounds like “sonic booms” shortly after the
time of the eruption (corresponding to the speed of sound travel-
ling across the globe), while weather stations in Denver, and
across the globe, recorded sudden pressure drops corresponding
to passage of the pressure wave. Later, analysis of satellite data
(Fig. 5) showed that the sonic blast was accompanied by the for-
mation of atmospheric gravity waves that formed from vertical
displacements of particles caused by the blast, from the sea sur-
face to the ionosphere. This is the first such documentation of
volcanically-induced gravity waves (Adam, 2022), and we spec-
ulate that their formation may have been aided by the sonic blast
moving through the dense eruption column that had already
reached to 20 km height, displacing the ash, and causing a ripple
effect that propagated throughout the entire atmosphere, and rap-
idly spread around the globe. The volcanic plume and sonic blast
were followed by a toxic cloud of sulfur dioxide, that was trans-
ported through parts of the Pacific by the remnants of a tropical
cyclone.
The displaced seawater caused a Pacific-wide tsunami, ini-
tially thought to be about 1–1.3 m in height in Tonga, but was
measured at up to 2.7 m in Japan. New reports from Tonga suggest
that the tsunami may have at least locally reached 15 meters, mak-
ing it one of the largest since the devastating Indian Ocean tsunami
of 2004 (e.g., Kusky, 2008a). At least one person in Tonga was
washed away in the tsunami, but the reports are not in from most
Timothy M. Kusky
230
of the islands at the time of this writing. The tsunami passed Ha-
wai’i, caused damage in Santa Cruz CA, Peru, and other locations,
while a few surfers in LA enjoyed the waves, surprisingly reaching
>1 m in places along the sunny California coast.
Most tsunami are caused by earthquakes that displace the
sea-bed, forcing water out of the way, which forms huge fast-
moving, large-amplitude tsunami. This one was different, and
apparently made prediction and warnings to Pacific-wide coastal
communities difficult. Preliminary interpretations (Yuen et al.,
unpublished data, based on observation from NASA) suggest
that the energy was released so explosively it was more like a
10-megaton atomic explosion, not a typical earthquake or vol-
canic eruption. Thus, this tsunami was different, and caused
more of a sloshing of the entire Pacific Ocean, and the atmos-
pheric gravity waves (Fig. 5) are possibly the cause of the 10–20
cm tsunami reported in the Caribbean and Atlantic Oceans.
Thus, we suggest that the Tonga tsunami was possibly caused
by the rapid incursion of seawater into a collapsing molten
magma-filled caldera, and from the preliminary observations,
seems remarkably similar to one of the most devasting volcanic
eruptions in recorded history; Thera, 3 650 years ago, in what
is now modern-day Santorini in Greece. The eruption of Thera
caused vast destruction across the Mediterranean and the down-
fall of the Minoan civilization that inhabited Crete at that time.
Let us look at what happened in the Mediterranean, 3 650 years
ago, to hopefully understand what we, as world citizens, can do
to help the people of Tonga, today. The background and histori-
cal accounts of the eruption of Thera, below, are excerpted,
adapted, and paraphrased from my book “Volcanoes: Eruptions
and Other Volcanic Hazards” (Kusky, 2008b).
Figure 1. (a) Map of the Tonga volcanic arc (from Plank et al., 2020) showing the location of Hunga Tonga-Hunga Ha’apai volcano relative to the Tonga trench,
the closest arc volcano to the main capital island of Tongatapu (lower center of the image). Inset map (box shows location of main figure) of the Tonga-Kermadec
arc-trench system is from Wikimedia Creative Commons Attribution-Share Alike 4.0 International License. (b), (c) Airbus Pleiades-1A image of the newly
formed cone that emerged from between the islands of Hunga Tonga (right) and Hunga Ha’apai (left) beginning on Dec. 19, 2014, and the new island as it
appeared on Sept. 19 2017 (from Garvin et al., 2018).
Déjà vu: Might Future Eruptions of Hunga Tonga-Hunga Ha’apai Volcano be a Repeat of the Devastating Eruption
231
Figure 2. Map of the Hunga Tonga-Hunga Ha’apai islands and submarine caldera complex (underwater). The map is by Shane Cronin (University of Auckland,
New Zealand), modifed after Cronin (2022). Compare with Fig. 1c for the emergent segments of the complex (in brown and green colors).
Santorini is a small, elliptically shaped archipelago (Fig. 6)
approximately 16 km across, located about 110 km north of the
island of Crete. These islands are dark and ominous in stark con-
trast to Greece’s other white limestone islands, and they form
ragged, 390-m peaks that seem to point up toward something that
should be in the center of the ring-shaped archipelago, but is no
longer there, ominously, like the Hunga Tonga and Hunga
Ha’apai islands that fringe the central caldera (Figs. 1b, 1c),
along with the new central island, that grew out of the sea from
volcanic eruptions in 2014–2015 (Garvin et al., 2018; Cronin et
al., 2017), and likely collapsed during the Jan. 15 eruption. The
peaks surrounding the caldera at Santorini are pointing in and up
toward the previous peak of a huge volcanic center, that col-
lapsed to form a giant caldera complex that erupted in the late
Bronze Age, approximately 3 650 years ago, devastating much
of the eastern Mediterranean. The largest island on the rim of the
caldera is Thera and across two circular 275–300-m-deep calde-
ras rest the opposing island of Therasia, once part of the same
volcano. The volume of material between, and below, was blown
away in the eruption, which currently seems to be the fate of at
least parts of Hunga Tonga-Hunga Ha’apai.
In the center of the composite caldera complex are several
smaller islands known as the Kameni Islands, which represent
newer volcanic cones growing out of the old caldera, much like
the new island between Hunga Tonga and Hunga Ha’apai that
emerged in late 2014 and 2015 (Garvin et al., 2018; Cronin et
al., 2017). Santorini and Thera are part of the Cyclades Islands
that form part of the Hellenic volcanic arc that stretches from
western Turkey through Greece, lying above a subduction zone
in the Mediterranean along which part of the African plate is be-
ing pushed beneath Europe and Asia (Meng et al., 2021). Volca-
noes in the Hellenic arc are widely spaced, and numerous earth-
quakes also characterize the region. The area was apparently
densely populated, as remnants of Bronze Age and earlier Neo-
lithic settlements and villages along the coastal Aegean are bur-
ied in ash from Thera.
Timothy M. Kusky
232
Figure 3. Two photos (taken looking eastward, from Tonga Geological Services) of the eruption at 5:27 p.m. Jan. 14, 2022, with a 5 km wide eruption column
rising to 20 km height. Hunga Ha’apai in foreground, Hunga Tonga at far right. Note that these photos capture the eruptions the day before the major sonic blast
eruption on Jan. 15, and may indicate the volcano was collapsing into the caldera.
Before the cataclysmic eruption, the Santorini Islands were
one giant volcano known to the Greeks as Stronghyle, or the
round one, and now referred to as Thera. We have no written
firsthand accounts of the eruption of Thera, so the history has
been established by geological mapping and examination of his-
torical and archaeological records of devastation across the Med-
iterranean region. Volcanism on the island seems to have started
1–2 million years ago and continues to this day. It will not end
until Africa finally collides with Eurasia, marking the final clo-
sure of the Tethyan seaway (Meng et al., 2021). Large eruptions
are known to have occurred at 100 000, 80 000, 54 000, 37 000,
and 16 000 years ago; then, finally, 3 650 years ago. The inside
of Thera’s caldera is marked by striking layers of black lava
alternating with red and white ash layers, capped by a 60-m-
thick layer of pink to white ash and pumice that represents the
deposits from the cataclysmic Bronze Age eruption. Ash from
the eruption spread over the entire eastern Mediterranean and
also on North Africa and across much of the Middle East. The
most violent eruptions are thought to have occurred when the
calderas collapsed and seawater rushed into the crater, forming
a tremendous steam eruption and tsunami. This is what we sug-
gest, based on very preliminary data, happened during the Jan.
15 Hunga Tonga-Hunga Ha’apai eruption. In the case of Thera,
the tsunami moved quickly across the Mediterranean, devastat-
ing coastal communities in Crete, Greece, Turkey, North Africa,
and the Levant. The tsunami was so powerful that it caused the
Nile to run backward for hundreds of kilometers. We are still
unable to assess the damage to the remote islands of Tonga.
Detailed reconstructions of the eruption sequence of Thera
reveal four main phases, that bear an uncanny resemblance to
what we know about the recent events at Hunga Tonga-Hunga
Ha’apai. The first was a massive eruption of ash and pumice that
was ejected high into the atmosphere, collapsing back on Thera
and covering nearby oceans with 3–4 m of pyroclastic deposits.
This phase was probably a Plinian eruption column and its
devastating effects on Thera made the island uninhabitable.
Approximately 20 years passed before some settlers tried to
reinhabit the island. This may be equivalent to the previous
months of very active Plinian eruptions from Hunga Tonga-
Hunga Ha’apai. For Thera, next, huge fissures in the volcano
began to open in the second phase, and seawater entered these
and initiated large steam eruptions and mudflows, leaving de-
posits up to 20 m thick. The third phase was the most cataclys-
mic, as seawater began to enter deep into the magma chamber
initiating huge blasts that were heard across southern Europe,
northern Africa, and the Middle East. Sonic blasts, much like
those accompanying the Jan. 15 Hunga Tonga-Hunga Ha’apai
eruption, and pressure waves would have been felt for thousands
of kilometers around. Huge amounts of ash and aerosols were
ejected into the atmosphere, probably causing several days of
virtual darkness over the eastern Mediterranean. The fourth
phase of the eruption was marked by continued production of
Déjà vu: Might Future Eruptions of Hunga Tonga-Hunga Ha’apai Volcano be a Repeat of the Devastating Eruption
233
pyroclastic flows depositing many layers of ash, pumice, and other
pyroclastic deposits around the island and nearby Aegean. Most
estimates of the amount of material ejected during the eruption fall
around 80 cubic km, although some estimates are twice that
amount. Ash layers from the eruption of Thera have been found in
Egypt, Turkey, other Greek Islands, and across the Middle East.
Thera undoubtedly caused global atmospheric changes af-
ter ejecting so much material into the upper atmosphere. Data
from Greenland ice cores indicate that a major volcanic eruption
lowered Northern Hemisphere temperatures by ejecting aerosols
and sulfuric acid droplets into the atmosphere in 1645 b.c.e.
Additional evidence of an atmospheric cooling event caused by
the eruption of Thera comes from tree ring data from ancient
bristlecone pines in California, some of the oldest living plants
on the planet. These trees, and other buried tree limbs from Ire-
land, indicate a pronounced cooling period from 1630 to 1620
b.c.e. European and Turkish tree ring data have shown cooling
between 1637 and 1628 b.c.e. Chinese records show that at this
time there were unusual acidic fogs (probably sulfuric acid) and
cold summers, followed by a period of drought and famine. The
eruption of Thera therefore caused not only the destruction of the
Minoan civilization, but also changed atmospheric conditions glob-
ally, forming frosts in California and killing tea crops in China.
Similar cooling of global temperatures occurred after other major
historical eruptions, including Tambora (1815) and Krakatoa
(1883), both in Indonesia, and Laki in Iceland (1783). Will Hunga
Tonga-Hunga Ha’apai have a similar effect? Will this on-going
eruption give us some time to try to correct global warming? Esti-
mates of the volumes of gases, ash, and the possible effects of the
atmospheric gravity waves on global atmospheric circulation are
just beginning at the time of this writing, so we don’t know yet. We
also do not yet fully understand what effect the atmospheric gravity
waves will have on global circulation patterns, or the effect on cli-
mate from this newly recognized phenomenon.
Figure 4. (a) GOES-West satellite image (US National Ocean and Atmospheric Administration) image of the sonic blast moving through the expanding eruption
column taken at 5:10 a.m. Jan. 15 GMT (1:10 p.m., Beijing time, 6:10 p.m. Nuku’alofa time). (b) Enhanced image (from Tonga Meteorological Services), showing
the location of the main island of Tonga, Tongatapu, with the capital city Nuku’alofa located near the center of the blast.
Timothy M. Kusky
234
Figure 5. Atmospheric gravity waves (from AIRS Level-1 data by NASA DES DISC) extending 16 000 km from the eruption, extending from the ocean surface
to the ionosphere, and traveled around the globe several times. From Adam, 2022 (with credit to Lars Hoffmann, Jülich Supercomputing Centre).
Figure 6. Map of the Santorini archipelago showing the two large calderas, surrounded by the islands of Thera and Therasia, much like Hunga Tonga-Hunga
Ha’apai (compare with Fig. 1). Map modified slightly from Kusky, 2008b.
Déjà vu: Might Future Eruptions of Hunga Tonga-Hunga Ha’apai Volcano be a Repeat of the Devastating Eruption
235
The eruption of Thera coincided with the fall of the Minoan
civilization, certainly in the Santorini archipelago, but also on
Crete and throughout the eastern Mediterranean. The cause of
the collapse of the Minoan society was probably multifold, in-
cluding earthquakes that preceded the eruption, ashfalls, and the
9-m tsunami waves that swept the eastern Mediterranean from
the eruption. Since the Minoans were sea merchants, the tsunami
would have devastated their fleet, harbor facilities, and coastal
towns, causing such widespread destruction that the entire struc-
ture of their society fell apart. Vessels at sea would have been
battered by the atmospheric pressure waves, covered in ash and
pumice, and stranded in floating pumice far from ports. Crops
were covered with ash, and palaces and homes were destroyed
by earthquakes. The ash was acidic, the same as from Hunga
Tonga-Hunga Ha’apai, so crops would have been ruined for
years, leading to widespread famine and disease. People sought
relief by leaving Crete, the homeland of the Minoan culture.
Many of the survivors are thought to have migrated to Greece
and North Africa, including the Nile Delta region, Tunisia, and
the Levant, where the fleeing Minoans became known as the
Philistines.
This lesson from history should not be forgotten. The erup-
tions from Hunga Tonga-Hunga Ha’apai are not over, and could
potentially be even worse in the coming days, weeks, and
months. The question is, what can we do to help the people of
Tonga, now, and for the future, so their culture does not have the
same fate as the Minoans. What can we learn from this eruption,
in terms of understanding Earth’s most powerful forces, and the
interaction of plate tectonics with climate, sustainability at local
and global scales? It is time to act.
Specifically, Tonga needs international aid to ensure that
their drinking water supply is safe, after contamination from the
acidic ash. This is difficult because the population is widely dis-
persed across many islands. Food will be needed if the existing
agricultural harvests have been destroyed and the fields acidi-
fied. On a longer scale, the international community can help
Tongans better understand, predict, and mitigate geological haz-
ards, and how to inform the communities what to do when more
earthquakes, eruptions, or tsunami occur. On an international
scale the scientific community can learn from this, in that we
need a new class of tsunami models for this type of eruption, as
the existing models seem inadequate to properly model this com-
plex system, and give residents of any ocean basin with similar
arc-related tsunami risks accurate information on evacuations or
emergency measures. Finally, with the exceptional monitoring
of this catastrophic event, the scientific community has a wealth
of new data on atmospheric gravity waves caused by massive
eruptions, and need to model potential effects on climate, and
unexpected types of tsunami generated by the atmospheric pres-
sure/gravity waves, and with better monitoring stations, of geo-
logically well-mapped and studied volcanoes, seismologists
might be better able to predict when such catastrophic eruptions
may occur. We must better understand the relationships between
tectonic processes on the planet, hazards to the places people
live, and the interaction between deep Earth processes, cata-
strophic events, their influence on the atmosphere, and how to
make a more livable sustainable planet.
ACKNOWLEDGMENTS
Data for this editorial were collected by the Tonga Geohaz-
ards team based in the Three Gorges Research Center for Geo-
Hazards, Center for Global Tectonics, China University of Geo-
sciences (Wuhan). Tonga Hazards Team: Timothy M. Kusky,
Louisa Meyers Pale, Susana Unaloto Ki He Vahanoa Takau,
Meletonga Kaituu, Jiannan Meng, Reda Amer. We thank Walter
Mooney and Dave Yuen for insightful discussions. The final pub-
lication is available at Springer via https://doi.org/10.1007/s12583-
022-1624-2.
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