Many people incorrectly think that continental Australia does not contain any active volcanoes.
However, the states of Queensland, Victoria, and South Australia all contain volcanoes
or volcanic fields defined as active as they have produced at least one volcanic eruption
during the last 11,700 years.
In South Australia and Victoria all of these recent eruptions occurred in a single vast
volcanic field which covers 21,500 square kilometers, being known as the Newer Volcanics
Province.
Vents in the Newer Volcanics Province are what are termed monogenetic as they erupt
once and then never erupt again.
This volcanic field has been erupting intermittently for 4.5 million years, creating a wide variety
of more than 400 vents via cinder cones, tuff cones, and most notably maars.
Maars are a type of volcanic explosion crater which are often larger than 50 meters wide,
and in the Newer Volcanics Province can be up to slightly more than 3 kilometers in diameter.
Many of these maars when they formed in powerful explosive eruptions dropped below the level
of the region's water table, and thus are today filled with crater lakes.
Examples include Lake Keilambete, Lake Gnotuk, and Lake Wangoom.
However, none of these features are quite as large or spectacular as another maar within
Victoria.
What I am referring to is the Tower Hill maar, which measures approximately 3,300 meters
wide and 80 meters deep.
Just imagine the scope of a volcanic eruption to carve out such a vast crater.
Around its walls you can find thick beds of volcanic ash and pyroclastic flow deposits
which are as much as 15 meters or 50 feet thick.
And yes, all of this thick material was emplaced in a single eruption which occurred 35,000
years ago.
This ancient eruption began as a body of magma was injected into the crust from the upper
mantle, moving upwards at a rate of several kilometers per day and eventually triggering
earthquakes and ground uplift of perhaps as much as 15 centimeters on the surface.
Finally reaching a depth of 500 meters, the magma began interacting with the region's
water table.
Due to the heat originating from the magma, the present groundwater quickly experienced
an increase in temperature which eventually caused it to flash to steam.
Since the same mass of steam takes up far more volume than the water it once was, it
caused an immense amount of pressure to build.
This pressure continued to grow until a powerful explosion occurred through the path of least
resistance which happened to be upwards, sending a tall plume of ash high into the atmosphere
and ejecting boulders of rock up to a distance of 1500 meters.
As this plume reached a height of perhaps as much as 12 kilometers, large amounts of
ash rained down, quickly going on to reach as much as 15 meters thick near the newly
formed crater rim edge on the eastern side as this represented the prevailing wind direction
at the time.
Part of the released gas was too heavy to rise into the atmosphere, so it collapsed
back to the ground as a series of ground hugging pyroclastic flows which scorched the landscape
in a several kilometer radius in all directions, even reaching up to 6,000 meters distant in
one direction.
As intermittent explosions continued which were less energetic, the crater got wider
and deeper.
Eventually, the shallow groundwater was largely absent, and an eruption which somewhat resembled
the 2021 eruption of the Cumbre Vieja volcano on the island of La Palma occurred.
Tall lava fountains were generated from a series of vents which were aligned in a south-southeast
direction.
While this occurred, intermittent explosions occurred, which ejected large volumes of scoria
and ash that built what is now the central island of the maar.
In total, the eruption which occurred would probably be rated on the volcanic explosivity
index as a 4, as it ejected at least 0.1 cubic kilometers of tephra.
Luckily, today Tower Hill is extinct and will never erupt again, although another location
in the vast Newer Volcanics Province will erupt again at some point in the future, most
likely at some point in the next 10,000 years.
However, since a volcanic eruption in the future can theoretically occur anywhere in
the vast volcanic field, nothing is preventing the next new vent from forming close by to
a preexisting one, such as Lake Gnotuk and Lake Bullen Merri which formed a mere 3,000
meters from one another.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below.
Additionally, I would like to thank this channel's patrons on Patreon and channel members on
YouTube!