Olympus Mons, a colossal mountain on Mars, holds the title of the largest known volcano in the entire Solar System. This immense geological feature dwarfs all terrestrial counterparts. While it has not erupted in millions of years, contemplating the reawakening of this giant provides a thought experiment. Understanding the potential consequences requires examining the volcano’s scale, the physics of a Martian eruption, and the unique conditions of the planet’s thin atmosphere.
Anatomy of the Martian Giant
Olympus Mons is a classic shield volcano, built up by countless flows of highly fluid lava over billions of years. Its enormous scale is a direct result of Martian geology and physics, specifically the planet’s low surface gravity and the absence of mobile tectonic plates. The volcano rises approximately 22 kilometers (14 miles) above the surrounding plains, making it nearly three times the height of Earth’s Mount Everest.
Its base spans 600 kilometers (370 miles), an area comparable to the state of Arizona. On Earth, plate movement would have carried the crust away from the magma hotspot, creating a chain of smaller volcanoes. Because the Martian crust remained fixed over a stationary plume of magma, material continuously piled up in a single location, allowing Olympus Mons to achieve its monumental size. This structure gives the volcano a very shallow average slope, despite its immense height.
The Likelihood of an Eruption
For a long time, Olympus Mons was considered extinct, having last produced a large-scale eruption around 25 million years ago. However, the designation has shifted to dormant, as evidence suggests it may not be completely cooled. Recent geological studies indicate that some lava flows on the flanks of Olympus Mons could be as young as 2 million years old, a mere blink in a planetary timescale.
The possibility of future activity is supported by the suspected presence of a vast, underlying magma plume beneath the Tharsis region, where the volcano is located. This deep magma reservoir appears to be slowly rising, suggesting that the Martian interior may still be geologically active enough to fuel an eruption. While the probability of an eruption in the near future remains extremely low, the planet’s crust is still capable of generating the “Marsquakes” that hint at subterranean movement.
Immediate Physical Devastation
A modern eruption of Olympus Mons would unleash a distinctly Martian pattern of devastation. The shield volcano’s basaltic magma would be highly fluid, and low Martian gravity would permit lava flows of unprecedented volume and distance. These low-viscosity flows would spill out across the Tharsis plains, potentially traveling thousands of kilometers before solidifying.
The shifting of the volcano’s internal plumbing would generate massive seismic events far exceeding any Marsquakes recorded to date. These tremors would destabilize large regions of the planet’s crust, potentially triggering enormous landslides and flank collapses around the Tharsis Bulge. The eruption would also launch an ash and dust plume of staggering proportions.
The extremely thin Martian atmosphere, which is less than one percent the density of Earth’s, would offer little resistance to the plume’s upward momentum. Models suggest that a powerful eruption could drive an ash column to heights exceeding 20 kilometers, injecting material directly into the upper atmospheric layers. This plume would contain far more dust and ash than an equivalent terrestrial event, given the low atmospheric pressure and the nature of Martian magma.
Global Climate Consequences
The long-term effects of a reawakened Olympus Mons would alter the Martian environment through the injection of massive amounts of volatiles. The eruption would release volumes of dust, ash, water vapor (H2O), and sulfur dioxide (SO2) into the atmosphere.
The initial climatic impact would involve a complex interplay of cooling and warming effects. The vast curtain of fine ash and dust particles injected into the atmosphere would block incoming solar radiation, likely causing a temporary global cooling. However, the simultaneous release of SO2 would introduce a powerful greenhouse gas that could potentially trap heat.
Volcanic sulfur dioxide on Mars would react differently than on Earth, potentially leading to warming of the lower atmosphere by several tens of degrees. The heat from the eruption could also melt widespread subsurface ice. This would rapidly vaporize the ice, releasing large amounts of water vapor that would increase atmospheric pressure and moisture content, even if only for a short geological period.