Around the planet at any given moment, there are between 40 and 55 volcanoes actively erupting.
Among these volcanoes, no two eruptions are alike.
Thus, to best understand the hazards an eruption might pose it is important to be able to identify
the type of eruption which is ongoing.
This video will briefly discuss the 14 types of volcanic eruptions and what types of volcanoes
most frequently produce them.
The most common type of volcanic eruption occurs in the vast oceans of the planet and
are referred to as submarine eruptions.
At great depths, the significant water pressure makes it almost impossible for any sort of
explosive volcanic activity to occur after a few hundred meters below sea level.
The majority of submarine eruptions are characterized by gentle lava effusion and a white column
of superheated water, steam, minor amounts of ash, and volcanic gasses which rise to
the surface.
A very similar eruption which occurs in locations such as the Andes, Alaska, Kamchatka, or Iceland
are sub-glacial eruptions.
Sub glacial eruptions almost entirely occur underneath a thick ice sheet, and many times
the eruption column never breaks the surface of the ice.
One way to know that a subglacial eruption is ongoing is due to a large sudden flood
of glacial water, termed a jokulhaup.
One example of a subglacial eruption was the 1996 eruption of Grimsvotn which released
3 cubic kilometers of water in a massive flood.
However, if a submarine eruption occurs at depths of less than 50 meters, it creates
an explosive eruption.
At these depths, magma explosively interacts with the surrounding water, generating a series
of short black ash rich explosions alongside a central white plume in what is termed a
surtseyan eruption.
On land, the most peaceful eruption type is known as an Icelandic eruption.
This type of eruption is characterized by a lengthy fissure or crack in the ground which
magma gently erupts from and spills out onto the sides.
The lava is then funneled to whichever direction is downslope, frequently forming rivers of
molten rock.
Icelandic style eruptions almost universally involve low silica basaltic magma, and originate
at or near divergent plate boundaries or rift zones on the planet such as near Lake Baikal
in Russia or central Iceland.
A similar eruptive type termed a "Hawaiian eruption" occurs when instead of a fissure
system, volcanic activity commences at either the summit of a shield volcano or a flank
vent.
In this type of eruption, lava is emitted alongside occasional small fragments of ash
out a vent via a tall fountain of material, which then falls back to the ground and gently
flows downhill.
If basaltic magma instead has a higher gas content, it can create the lowest magnitude
of what can be correctly considered an "explosive eruption".
In a so-called "strombolian" eruption, fluctuating bursts of volcanic gasses and small explosions
propel fragments of lava high into the air and fling them up to several hundred meters
distant.
Moderate amounts of ash also are emitted from the erupting vent in a process which is particularly
loud.
Strombolian eruptions often result in the formation of cinder cones such as witnessed
during the 2021 eruption of La Palma in the Canary Islands.
At stratovolcanoes, the most common type of eruption occurs when lava or related volcanic
products temporarily clog an eruptive conduit.
Pressure than builds up until an explosion occurs, ejecting a thick cloud of ash.
This is what occurs during "vulcanian" explosive eruptions, which are best identified via the
small pyroclastic flows they produce.
These vulcanian explosions are separated by periods of relative inactivity which last
between a minute and 36 hours.
However, a vulcanian eruption can also occur when the side of a lava dome is unstable,
and blocks of it fall off, releasing pyroclastic flows.
This is what occurred at Mount Unzen in 1991, and some of my colleagues refer to this as
a Merapi type vulcanian eruption.
This fact might surprise some people, but there is an entire class of volcanic eruptions
which does not eject any lava.
In phreatic eruptions, underlying magma stays at depth and heats nearby groundwater.
The heated groundwater then flashes to steam, and since steam takes up more space than the
same mass of liquid water, it triggers a powerful explosion.
Phreatic eruptions may occur as unique events, but are most commonly witnessed in the early
stages of a magmatic eruption.
If a phreatic eruption is large enough, or if the magma triggering the eruption is quite
shallow, small fragments of lava can be ejected in what is termed a phreatomagmatic eruption.
Aforementioned vulcanian and phreatomagmatic eruptions do not typically produce a sustained
eruption column, but instead produce intermittent plumes.
If an eruption does have a sustained plume, lasting on the order of several hours to days,
it is a plinian eruption.
During plinian eruptions, significant quantities of ash are ejected high into the atmosphere,
often reaching the stratosphere.
It is quite common for part of the eruption column to collapse downwards, creating long
travelling pyroclastic flows.
If a sustained eruption plume is less than 20 kilometers in height, it is a sub-plinian
eruption.
If it is greater than 20 kilometers, it is a plinian eruption.
If a plinian eruption occurs through a water rich layer of a lake or glacier, an eruption
plume may have a whiteish gray color in what is called a phreatoplinian eruption.
And, if an eruption with a sustained eruption column ejects more than 10 cubic kilometers
of explosively erupted material, it is called an ultraplinian eruption.
The final type of volcanic eruption gets its namesake due to the famous 1902 eruption of
Pelee in the Caribbean, a pelean eruption.
Pelean eruptions occur when large amounts of pressure and gasses build underneath a
volcano.
After reaching a critical point, a powerful explosion occurs, often occurring to the side
of a volcano in a lateral blast or being heavily focused towards a single direction.
This generates long reaching pyroclastic flows, which travel much further then seen at most
vulcanian or sub-plinian eruptions.
At some point in the eruption before, during, or after the peak explosive phase, a lava
dome is often constructed.
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