When most people think of the word volcano, they picture a circular cone with a triangular profile.
However, not all volcanoes look like this. Take for example this explosion crater in Mexico.
This is a volcano. Or this rare volcanic feature in British Columbia with a flat top.
This is also a volcano. This video will briefly
cover the varieties of volcanoes which form around the globe, and explain how they form.
The first type of volcano we will cover is also the most simplistic; fissure volcanoes. A fissure
volcano does not have a central peak, but rather is defined by a series of straight line cracks in
the crust known as fissures. These fissures are typically the result of the two tectonic plates
spreading apart. During a fissure eruption, lava erupts from a long section of a fissure,
and slowly travels downslope. The majority of the world's oceanic crust was formed by
this type of volcano which erupts on a near constant at Mid ocean ridges around the planet.
One example of a fissure volcano which you can see on land is at the Bárðarbunga volcano in Iceland.
The second type of volcano can occur as a unique volcano, or be part of a vent on a much larger
volcano. What I am referring to are cinder cones, which are a type of medium sized volcanic cone.
Cinder cones have a cylindrical shape with a central vent, and are formed by mildly
explosive eruptions. During these eruptions, fine particles of ash are ejected from the
volcano and largely fall close to the erupting vent, thus building the cone.
One notable cinder cone is Paricutin in Mexico. The third type of volcano is a shield volcano.
These form from the effusive eruption of low viscosity lavas which move relatively quickly.
Due to this fast movement speed, the lavas are deposited far from the erupting vent and
thus build a very gentle slope. The largest volcanoes in the world are shield volcanoes,
with one example being Mauna Loa in Hawaii. A stratovolcano has the stereotypical profile
of a volcano, with a relatively steep slope which increases up until the peak
of the mountain. Stratovolcanoes are built from a combination of layers of ash from
explosive eruptions overlaid with viscous lava flows. Stratovolcanoes are generally
built out of andesite or basaltic andesite and as a result have a distinguishable gray color.
When highly viscous lava erupts onto the surface, it often forms a dome shaped feature with a
steep drop-off at the edge of a flow. Sometimes, volcanoes can be built by a combination of these,
and are thus termed lava dome complexes. The Lassen Peak volcano is a perfect example of this,
as one of its recent eruptive centers contains four overlapping domes of dacite lava.
The most catastrophic eruptions in the world often eject many cubic kilometers worth of lava and ash.
When this occurs, it can cause the underlying magma chamber at depth to drain, causing
structural instability in the crust overlying it. Sometimes, the crust collapses downwards to fill
the pockets of air in the magma chamber, which forms a circular depression in the ground known as
a caldera. These calderas are typically at least 2 kilometers across, but in some circumstances
can form to be more than 100 kilometers across after the eruption of a supervolcano.
The feature shown on screen has a flat top and very steep slope. This rare volcanic feature
is known as a tuya, and is built out of andesite. Tuyas form from eruptions beneath a thick glacier
or ice sheet. The lava during these eruptions cannot escape a section of the overlying ice,
thus forming a flat top. One example of a tuya is "the table" in the Garibaldi Lake volcanic field.
It may seem strange, but some volcanoes never erupt any lava. Take for example this giant
explosion crater at the Soda Lakes volcano in Nevada. It contains two explosion craters,
one of which is two kilometers wide. These craters are referred to as "maars",
and form when heated rock encounters groundwater at depth. The groundwater then flashes to steam,
and explodes thus forming an explosion crater above it.
A similar volcanic feature known as a "tuff ring" forms when the same process
takes place, but instead with a body of water on the surface. When this occurs, an explosion
crater is generated but is not as deep, and has a highly rounded ring of debris at the crater's
edge. This tuff ring in the Pinacate volcanic field in Mexico is known as Cerro Colorado,
and is 40 meters deep and a kilometer wide. Several other less common volcanic types exist on
the planet, but the 9 which I just listed account for 99.9% of volcanoes worldwide. I hope that you
enjoyed this video. If you would like to request a specific topic, please leave a comment below!