Since the turn of the 20th century, there has been a relatively consistent number of
actively erupting volcanoes, which has averaged between 40 and 50 at any given moment.
However, since then something else has not remained constant.
Around the planet, human activity has led to an increase of carbon dioxide in the atmosphere,
leading to the increase of worldwide temperatures by 1 degree celsius or 1.8 degrees fahrenheit.
This has caused sea levels to rise by 20 centimeters and for the majority of glaciers around the
world to retreat.
However, the purpose of this video is not to explain the complexity of human caused
climate change.
Rather, it will explain why the rate of volcanic eruptions around the planet is likely to increase
in some areas and decrease in others as the planet warms.
Before I say why this will occur, I'll state which parts of the planet will likely see
a change in the frequency of volcanic eruptions.
Across the planet, the rate of volcanic eruptions will increase at many volcanoes covered by
a series of glaciers or some form of massive ice sheet.
Such is the case for many volcanoes in Iceland, Alaska, Canada, Russia, Antarctica, far southern
Chile, and taller volcanoes in the Andes mountain range.
Meanwhile, the rate of volcanic eruptions will decrease slightly at shallow submarine
volcanoes such as Campi Flegrei Mar Sicilia off the southern coast of Italy and a slightly
weaker decrease in eruptive frequency at volcanoes which have most of their bulk volume below
sea level such as Mount Stromboli.
To understand why this will occur I present an example; the Westdahl volcano in Alaska.
Westdahl is a large stratovolcano located southwest of the mainland on Unimak island
which is mostly covered by a series of glaciers which are around 1 kilometer or 3,280 feet
thick.
At a depth of 4.5 miles or 7.2 kilometers beneath Westdahl's summit is a large body
of magma.
Ever since it last erupted in 1992 this deep magma chamber has been slowly receiving a
steading influx of new material, increasing the pressure within this reservoir.
Once the pressure in this magma chamber is greater than that exerted on the rock overlying
the molten material, equilibrium is lost, and dike propagation begins.
Once this occurs, it is often only a matter of time before a new volcanic eruption starts.
If this volcano did not have any glacial cover, models suggest it would have certainly erupted
by 2010.
However, it is now September of 2022 and an eruption has not yet occurred.
Although ice is less dense than the average volcanic rock, a several kilometer thick sheet
of it increases the amount of pressure a magma chamber must have before dike propagation
can occur, making volcanic eruptions far less frequent.
In a scientific paper by L. Lucas and others, linked below, they modelled how reduced the
rate of eruptions would be depending on glacial thickness and depth of a volcano's magma chamber.
They found that if a prolate magma chamber at a depth of 2 kilometers without an ice
sheet normally erupted every 100 years it would instead erupt once every 186 years with
a 3 kilometer thick ice sheet above it.
If the same magma chamber was instead located at 9 kilometers depth then the volcano would
erupt an average of once every 112 years.
As glaciers retreat around the planet, the pressure required for dike propagation to
begin and potentially lead to an eruption decreases meaning that eruptions will occur
more frequently.
As modelled by the aforementioned paper, this could result in increases in eruptive frequencies
in the double-digit percentile range at various volcanoes that have glaciers assuming part
of or the entire glacier on them melts away.
In theory, resulting eruptions from these volcanoes would then on average be slightly
less explosive than beforehand.
Also, although the paper did not conclude this, the same logic could likely be applied
to the weight of water on a primarily submarine volcano.
Thus, as ice caps around the world melt and drain into the ocean, sea levels will rise,
increasing the pressure on primarily submarine volcanoes and reducing their rate of new eruptions.
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