The year was 1951, and the location was Papua New Guinea.
People were going about their daily lives when something unexpected occurred.
One of the local mountains which was highly eroded started to smoke.
This was not from a forest fire, but rather from a volcanic eruption.
Over the next four days, the eruption became more obvious, causing the several thousand
residents who lived nearby to take note, even recording the unexpected nature of the eruption
as no one locally had previously thought Mount Lamington was a volcano.
Then, on January 21st, at 10:40 am local time, one of the world's deadliest volcanic eruptions
occurred.
Part of Mount Lamington unexpectedly collapsed, creating a several kilometer long landslide
of rock.
From this landslide emerged pyroclastic flows which raced downhill in every direction, travelling
up to 14 kilometers distant and destroying everything in their path.
After several additional powerful explosions occurred, the extent of the disaster which
had unfolded became clear.
More than 300 square kilometers of forest, consisting of many towns and villages, had
been completely incinerated.
This caused between 2,500 and 4,000 casualties and the eruption was assigned a volcanic explosivity
index of a 4.
So, how did this deadly eruption occur?
For context, the Mount Lamington volcano is located in far southeastern Papua New Guinea,
where it is 120 kilometers east northeast of Port Moresby.
This volcano is one of several regional volcanic centers which form a narrow chain of activity.
These volcanoes formed due to a unique geologic setting, where to the north the Trobriand
Trough marks the edge of a plate boundary that once subducted towards the south underneath
a large tectonic plate.
However, this subduction is no longer ongoing, and as a result a slab of material has likely
broken off.
Partial melting then occurred on this slab, and due to a divergent plate boundary to the
south caused upwelling of the mantle and created a series of weak points, allowing for magma
to intrude into the crust and erupt onto the surface.
Mount Lamington began forming approximately 90,000 years ago, when a volume of this magma
intruded into the crust.
As it continued shallower into the crust, the magma became defined by a north-northeastern
fissure.
When it finally reached the surface, it erupted in an explosive manner.
As a gray column of ash rose into the atmosphere, bits of rock and lava were intermittently
ejected.
Then, since the lava which erupted had a high viscosity, it could not flow very far from
its source vent and solidified into a large lava dome.
After a 1 kilometer long and 200 meter tall lava dome was constructed, the eruption ceased.
Following a several thousand year long period of dormancy, Lamington erupted again, producing
another lava dome 7 kilometers to the west.
The next series of eruptions created lava domes back at the site of the first vent,
which began to overlap each other after tens of thousands of years of activity.
When the volcano erupted again in 1951, a small phreatic eruption initially occurred,
as the intruding magma was confined by the edifice of the volcano.
Over the span of several days, a bulge appeared on the northern section of the mountain, creating
an appearance somewhat similar to what was witnessed at Mount Saint Helens before it
catastrophically erupted in 1980.
Then, on January 21st, the northern slope of the volcano collapsed in a large landslide,
traveling up to 10 kilometers from its source.
This released a large volume of underlying pressure and exposed a section of the magmatic
intrusion, causing a powerful pelean style eruption to occur.
As a plume of ash rose more than a dozen kilometers into the atmosphere, part of the eruption
column collapsed due to its mass, travelling across the landscape in all directions as
superheated pyroclastic flows.
Additionally, a lateral blast was directed outward from the collapsed section of the
volcano, incinerating everything up to a distance of 14 kilometers in mere minutes.
For a period of 5 years following this eruption, a large lava dome grew out of the 1.3 kilometer
wide collapse scar generated by the events in 1951.
Then, the eruption ended.
As to why Lamington did not look like a volcano before its 1951 eruption?
It relates to how fast the dense rainforest vegetation reclaims destroyed landscape, which
often takes less than 50 years in this part of the world.
Thus, if a volcanic complex has not produced an eruption is living memory of the people
nearby, it is often not recognized as a volcano.
For example, the Waiowa volcano produced an eruption from 1943 to 1944, but its eruption
site is no longer recognizable since it is now densely forested.
Thanks for watching.
If you would like to request a specific topic, please leave a comment below!
Additionally, I would like to thank my grandidierite tier patron Justin who requested this video's
topic!