On Mars, Mount Olympus, or Olympus Mons, as it is known in Latin, is the Solar System's
largest known volcano.
It is a shield volcano.
Rather than violently spewing molten material, shield volcanoes are created by lava slowly
flowing down their sides.
The massive shield volcano is almost practically made up of basalt lava flows.
It towers about 16 miles (25 kilometers) above Mars' surface and has a diameter of 374 miles
(600 kilometers), making it roughly the size of Arizona.
It would just about fit within the boundaries of France.
It is so enormous that it could be recognized as a separate feature on telescopes as early
as the 19th Century.
But it wasn't until 1971, when NASA's Mariner 9 spacecraft arrived in orbit around Mars,
that the nature of Mount Olympus was established not only as an outstanding mountain but also
a volcano.
This volcano, which is roughly three times the height of Mount Everest (the highest point
on Earth), must have had a lot of activity and eruptions to grow to the size it is now.
Because Olympus Mons is so large, the lava must have been quite runny, resulting in the
smooth slopes that are seen.
However, scientists don't believe the volcano has erupted recently.
They believe it last erupted about four billion years ago, and because of this, they concluded
that it is a dormant volcano, one that is at rest because there isn't much lava movement
visible.
After reviewing many photographs and scientific data obtained by satellites and rovers on
Mars, they came to this conclusion.
Also, they examined the rock in great detail and calculated the ages of the rocks visible
on the surface.
The rocks on the surface are cold since they have had plenty of time to cool down from
the last time they erupted from the volcano.
The average temperature of Mars today is -63°C, which is quite low!
Temperatures must be extremely high for a volcano to erupt and melt rocks into lava.
So Olympus Mons would have been far hotter billions of years ago.
When lava erupts from volcanoes on Earth, it can reach temperatures of 700°C to 1,200°C.
Volcanoes in Hawaii are more or less similar to Olympus Mons in that they have very wide
bases and very gentle slopes.
Although the volcanoes in Hawaii are much smaller, they are very similar.
When lava gets hotter, it becomes runnier, and we know that the lava on Olympus Mons
was runny because of the lengthy slopes observed.
So, the lava must have been extremely hot for it to be runny, and if it was similar
to the volcanoes in Hawaii, the lava would have been around 1,200°C.
If the lava had been any colder, it would not have been able to flow down the sides
of the volcano, resulting in extremely steep slopes as it accumulated up near the top of
the volcano.
This would result in the formation of a different type of volcano known as a stratovolcano.
These types of volcanoes exist here on Earth, such as Mt St. Helens in the United States.
Why would such a massive volcano erupt on Mars but not on Earth?
Scientists think that the red planet's lower surface gravity, combined with faster eruption
rates, allowed the lava to pile up higher.
The presence or absence of tectonic plates may also impact the different types of volcanoes
that exist.
On both planets, the lava hot spots under the crust remain in the same location.
However, the movement of the crust on Earth hinders the continuous build-up of lava.
For example, the Hawaiian Islands formed as a plate drifted over a hot spot.
Each eruption resulted in the formation of a little island in a different spot.
However, plate movement on Mars is quite limited.
Both the hot spot and the crust have remained stationary.
When lava reaches the surface, it piles up in a single spot.
Large volcanoes, such as Olympus Mons, form instead of a series of volcanic islands.
Although we can't visit Olympus Mons in person, we can learn a lot about the rocks and how
they formed by using satellites and rovers, as well as comparing them to similar volcanoes
here on Earth.
The more we learn about Mars as a planet, the more we'll be able to determine its past
environment and how it evolved into what we observe today.
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