Question

Volcanoes, such as the Hawaiian chain, that form over mantle plumes are some of the largest on Earth. However, several volcanoes on Mars are gigantic compared to those on Earth. What does this difference tell us about how, or if, the process of plate motion operates on Mars? Explain.

Short answer

Mars likely lacks active plate tectonics, allowing volcanoes to grow much larger than on Earth.

Step-by-step solution

Understanding Plate Motion

Plate tectonics involves the movement of large plates on a planet's surface due to the heat-generated activity within. On Earth, these moving plates can lead to volcanic activity when a plate moves over a mantle plume, forming a chain of volcanoes. The continuous movement of plates creates new volcanoes and eventually subducts older ones.

Comparing Mars and Earth

Mars has some of the largest volcanoes known, such as Olympus Mons, which is much bigger than any on Earth. This suggests that Mars does not have active plate tectonics like Earth because if it did, the plates would distribute volcanic activity and prevent the formation of such massive single volcanoes over time.

Implications of Stationary Crust

The enormous size of Martian volcanoes implies that Mars' crust is relatively stationary, allowing mantle plumes to build up a single, large volcano in one location over a long period. Without plate motion, the volcanoes continue to grow larger without being shut down or relocated.

Key concepts

Mantle Plumes

Mantle plumes are upwellings of abnormally hot rock that originate deep in a planet's mantle. As these plumes rise towards the surface, they can cause melting, which leads to volcanic activity.
The Hawaiian Islands are a classic example of how mantle plumes create volcano chains on Earth. As the Pacific Plate moves over a stationary mantle plume, melting occurs in the mantle, and magma rises to create new volcanoes.

• This process forms new islands over millions of years, with older ones subducting back into the mantle or eroding away.
• Therefore, Earth's dynamic plate movement results in multiple small volcanoes forming over time, rather than one large one.

On Mars, the absence of active plate tectonics means mantle plumes can build massive volcanoes like Olympus Mons, as they remain stationary beneath Mars’ crust for extended periods. This allows a single volcano to grow vast over millions of years.

Plate Tectonics

Plate tectonics is the theory explaining the movement of large plates that make up a planet’s crust and lithosphere. This concept is key to understanding planetary volcanism, especially on Earth.
The movement is driven by heat from the planet’s core, causing convection currents. On Earth, these currents shift crustal plates, which can lead to the formation of volcano chains as plates move over hot spots, or mantle plumes.

• As plates subduct or collide, pressure and temperature changes can lead to volcanic activity.
• The formation of ocean basins, mountain ranges, and island arcs are all influenced by plate tectonics.

In contrast, Mars's crust seems to be more rigid and stationary. Without plate movements to distribute volcanic activity, a mantle plume under Mars can continue feeding the same volcano repeatedly, resulting in enormous structures like Olympus Mons.

Martian Geology

Martian geology provides fascinating insights into how planetary geology can differ due to varying internal processes. Mars showcases enormous shield volcanoes, ancient river valleys, and vast dust storms, indicating geologic activity both past and present.
Olympus Mons, towering 13.6 miles high, is proof of Mars' unique volcanic history. The volcano's size suggests that Mars has what resembles a single piece crust, unlike Earth's dynamic, fragmented plates.

• Without plate tectonics, magma can continuously supply volcanoes with material, resulting in their immense size.
• Furthermore, Mars' lower gravity and lack of atmospheric erosion help sustain these gigantic structures over time.

Mars' geology, complete with features indicating water flow in its past, hints at a once more active and possibly hospitable surface environment, making it a compelling study for planetary scientists.