Overview
This lecture discusses why volcanoes on Mars, specifically Olympus Mons, are the largest in the solar system and compares volcanic processes on Mars and Earth, focusing on the role of plate tectonics and hotspots.
Volcanoes on Mars
- Some Martian volcanoes are so large they are visible from space.
- Mars, despite being a small planet, has the largest volcanoes in the solar system.
- Olympus Mons is the tallest and widest volcano, named after Mount Olympus.
- Olympus Mons is about as wide as the state of Arizona and over two and a half times taller than Mount Everest.
- The caldera (top crater) of Olympus Mons is larger than the state of Rhode Island.
Formation and Growth of Martian Volcanoes
- Mars has a crust with an asthenosphere (partially molten upper mantle) beneath it.
- Hotspots (hot areas in mantle) heat magma causing it to rise via convection.
- Rising magma breaks through the crust, forming a volcano above the hotspot.
- If the hotspot remains active, continuous eruptions add more rock, making the volcano grow very large.
- Martian volcanoes grew so big because hotspots stayed under the same location for long periods.
Why Earth's Volcanoes Are Smaller
- Earth also has a crust, asthenosphere, mantle, and hotspots.
- Earth’s crust moves due to plate tectonics, but hotspots stay stationary.
- When a volcano moves off a hotspot, it becomes inactive and erodes.
- New volcanoes form as the plate moves over the hotspot, creating a chain of smaller volcanoes rather than one giant one.
- Example: Hawaii is a chain of volcanic islands formed by a hotspot, with only the islands directly over the hotspot currently active.
- Older Hawaiian islands erode and submerge as the plate continues moving.
Plate Tectonics vs. Stationary Crust
- Without plate tectonics, a hotspot would create one or two enormous volcanoes, like on Mars.
- With plate tectonics, Earth has many smaller volcanoes in chains rather than single large volcanoes.
Key Terms & Definitions
- Hotspot — an area of the mantle that is significantly hotter than its surroundings, leading to volcanic activity.
- Asthenosphere — a region of the upper mantle beneath the crust, involved in plate movement and volcanism.
- Caldera — the large crater at the top of a volcano formed after an eruption.
- Plate Tectonics — the movement of Earth's crustal plates over the mantle, causing earthquakes, volcanoes, and mountain formation.
Action Items / Next Steps
- Review diagrams of hotspot volcanism on Mars and Earth.
- Compare volcanic chains (e.g., Hawaii) and single volcanoes (e.g., Olympus Mons) for upcoming quiz.