Within Katmai National Park and Preserve in Alaska is a strange geologic oddity.
There, 14 miles north-northeast of the active Griggs stratovolcano is a circular depression
in the ground.
Known as Savonoski Crater, it measures 1,738 feet or 530 meters wide and from its rim to
the water surface in the crater lake is 164 feet or 50 meters.
Looking at this feature you might think, "wow, this is a fascinating impact crater, albeit
a fairly small one", and for many years, this feature was thought to be an impact crater.
However, more than 50 years after its discovery, we are no closer to discovering the true origin
of this circular structure than we were in the 1970s.
The main problem revolves around the following issue.
Most impact craters exposed on Earth's surface that happened to have formed in the last 5
million years show a notable feature.
That is, they formed in areas that have large surface exposures of sedimentary or metamorphic
rock.
And, in the rare chance the impact crater formed on top of volcanic rock, the solidified
lava, ash, or other magmatic products are generally many millions if not billions of
years older than the exposed surface of the crater.
However, at volcanoes around the planet, there is a type of volcanic vent which looks just
like an impact crater.
For example, in Oregon there is the 1 mile wide and 360 foot deep feature simply known
as "hole in the ground".
This feature formed during a voluminous explosive eruption when one of the adjacent volcanic
complexes produced a magmatic intrusion.
As the magma advanced upwards, the heat of the material transferred through the crust,
heating ever present groundwater.
Eventually, this water flashed to steam, and since the same mass of steam takes up significantly
more volume than the water it once was, it caused an immense amount of pressure to build.
After reaching a critical point, a powerful explosive eruption occurred, creating a large
explosion crater known as a maar which did not erupt any lava.
Thus if a meteorite or small asteroid was to strike a volcanic area around the same
time it was erupting or highly active, how would scientists be able to determine its
origin?
And this is exactly the problem at Savonoski Crater.
Although the closest volcano to Savonoski Crater is Mount Griggs, a total of 11 volcanoes
are within a 33 mile or 53 kilometer radius, marking it as one of the most volcano rich
areas on the planet.
You might ask why I chose the seemingly arbitrary number of 33 miles.
The answer is that this distance represents the furthest away a vent in an active volcanic
complex can be from another vent at least that I am aware of, excluding true fissure
complex volcanoes such as seen in Iceland.
Thus, any one of these 11 volcanoes could have theoretically created this crater.
This possibility is supported by the fact that 5 small volcanic cones are located in
relatively close proximity to Savonoski which all formed in the last several million years.
However, these two ideas are not the only legitimate possibilities to consider.
Looking around areas in cold climates from satellite, you might notice an absurdly high
number of depressions in the ground which often have lakes and can sometimes be surprisingly
circular.
These features are known as kettles, and form during the process of glacial retreat.
During this process, chunks of the glacier or individual blocks of ice break off and
are left behind by the retreating glacier.
They are later buried by sediment, and thus when they finally melt, they leave a depression
in the ground.
And, if this depression dips below the water table, the kettle fills with water.
This is why large sections of Alaska, Canada, Russia and other areas that used to be covered
by numerous glaciers have many thousands of these features.
The final possibility revolves around the recent discovery of natural gas explosion
craters in the permafrost of Russia.
After a pocket of natural gas reaches a certain pressure, it may violently shoot upwards via
a path of least resistance, which sometimes forms a crater.
However, this possibility seems the least likely of the group as I could not find any
record of nearby natural gas deposits in this section of Alaska.
Thanks for watching!
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