Approximately 790,000 years ago, a truly devastating geologic cataclysm occurred on Earth.
And yet, for a very long time this destructive event was largely forgotten.
That was until a connection was noticed between a series of rocks such as this one.
While this specimen is a variety of naturally made glass it is not obsidian, although the
two do have similar appearances.
These pieces of glass were found from the same approximate moment in geologic history
in Mozambique, Madagascar, Antarctica, India, Australia, China, Indonesia, The Philippines,
far southern Japan and other areas.
These fragments of glass are thus found over 15.4% of Earth's total area on land and oceans
combined.
Thus, this glass was not formed by a powerful volcanic eruption or even a supervolcano but
instead something far more energetic; the largest asteroid impact Earth had experienced
in the last 2.5 million years.
Thus, these pieces of glass are referred to as tektites, with the entire strewnfield they
encompass being known as the australasian strewnfield.
For context, tektites are pieces of impact glass which form when a fairly sizable impact
event occurs.
This impact pulverizes large swaths of rock at the impact site but due to its high speed
which is often more than 15 kilometers per second it causes some fragments of rock to
almost instantaneously melt into glass before being ejected several kilometers into the
atmosphere.
These pieces then cool and fall back to the ground as tektites.
Tektites are generally a black color, but as shown by the occurrence of Moldavites in
eastern Europe from a 14.8 million year old impact event in Germany, they can also be
green.
For several decades, it remained a mystery as to where the Australasian tektites originated,
and a number of hypothesises were proposed.
Yet, as time progressed scientists finally narrowed in on where the source impact crater
was; somewhere in the vicinity of either Cambodia, Laos, Thailand, or Vietnam.
Yet, looking from satellite these areas do not have any obvious minimum 10 miles or 16
kilometer wide impact structures.
For comparison, look how obvious and well preserved the Bosumtwi Crater is in Ghana
which measures 10.5 kilometers across and is slightly more than 200,000 years older
than the expected crater.
So, where on Earth is this missing crater?
The answer only finally arrived in the last decade, when the crater was finally found
in the nation of Laos.
There, a 19.5 kilometer long and 15.0 kilometer wide impact crater was found surrounding albeit
mainly slightly north of the city of Paksong.
And, the reason this impact structure was so hard to find is that in the time since
it formed it was buried by more than 500 meters thick of lava.
As, although few people know about this, southeast Asia does contain a few scattered dormant
and active volcanoes and volcanic fields.
The volcanic field in question is currently dormant and is known as the Bolaven Volcanic
Field.
It covers an area slightly larger than 8,000 square kilometers and has been erupting intermittently
since approximately 16 million years ago.
This field consists of low silica primarily basaltic lava which has formed cinder cones
and has erupted individual lava flows which have travelled up to 35 kilometers from their
source vent.
It has erupted 15 times in the last 135,000 years including two lava flows which are under
40,000 years in age.
Altogether this volcanic field has erupted on average about once every 10,400 years.
And, either through sheer coincidence or possibly because of the asteroid impact itself, the
highest concentration of volcanism in this volcanic field in the last 790,000 years was
clustered within the impact structure.
This could be because it represented a path of least resistance after a 700 meter deep
crater was carved into the ground, but the impact itself could have also generated a
volcanic eruption as shown via an impact event on Mars around 110,000 years ago.
While the exact effects of the Laos impact event are unclear, models suggest the energy
released during the event may have been equivalent to around 428,000 megatons of TNT detonating
simultaneously.
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