Mars Volcanoes Are Far More Complex Than Scientists Believed

The Red Planet's Volcanic History Needs a Major Rewrite

Mars has always been known for its volcanoes. Olympus Mons, the tallest volcano in the solar system, has been a fixture of planetary science textbooks for generations. But scientists have long assumed that Martian volcanism was relatively simple: basaltic eruptions building broad shield volcanoes over billions of years, with little of the compositional diversity seen on Earth. A new study is upending that comfortable narrative, revealing that Mars's youngest volcanoes display a startling complexity that rivals anything found on our own planet.

The research, based on high-resolution orbital data combined with advanced spectral analysis, has identified volcanic deposits on Mars that span a far wider range of chemical compositions than previously recognized. These include silica-rich lavas that would have been viscous and explosive, pyroclastic deposits indicative of violent eruptions, and evidence of volcanic activity far more recent than most models predicted.

Challenging the Basalt Monotony Myth

For decades, the prevailing view of Martian volcanism was one of relative monotony. Mars was thought to produce mainly basaltic lavas, the same type of low-viscosity, iron-rich lava that builds Hawaiian shield volcanoes on Earth. This assumption was supported by early orbital and lander data, which consistently detected basaltic compositions on the Martian surface.

But the new analysis tells a different story. Using data from multiple orbital spectrometers with overlapping wavelength ranges, the research team identified volcanic deposits with compositions ranging from basalt to dacite, a silica-rich rock that on Earth is associated with explosive, often dangerous volcanic eruptions.

The discovery of dacitic compositions on Mars is particularly significant because producing dacite requires a process called fractional crystallization, where magma evolves chemically as it slowly cools and different minerals crystallize out at different temperatures. This process requires either large, long-lived magma chambers or repeated remelting of previously erupted material, both of which imply a more complex volcanic plumbing system than Mars was thought to possess.

The Young Volcanoes of Elysium Planitia

The most surprising findings come from the Elysium Planitia region, a broad volcanic plain in Mars's northern lowlands. While the giant volcanoes of the Tharsis region have attracted most scientific attention, Elysium has emerged as a hotspot for recent volcanic activity.

The team identified a cluster of small volcanic constructs in Elysium that appear to be remarkably young, potentially less than 100 million years old and possibly as young as a few tens of millions of years. In geological terms, this is practically yesterday. These young features include:

• Steep-sided domes: Structures resembling the volcanic domes produced by viscous silica-rich lava on Earth, very different from the broad, gently sloping shields typical of basaltic volcanism.
• Pyroclastic mantling deposits: Layers of fine-grained material draping the terrain around volcanic vents, consistent with explosive eruptions that ejected fragmented rock and ash into the Martian atmosphere.
• Compositional zoning: Systematic variation in chemical composition from the center of volcanic features to their edges, suggesting that eruptions tapped magma at different stages of chemical evolution.
• Lava flow morphologies: Flow textures ranging from smooth pahoehoe-like surfaces to rough blocky surfaces, indicating a wide range of lava viscosities and eruption temperatures.

What Drives Compositional Diversity on Mars?

The existence of evolved volcanic compositions on Mars raises fundamental questions about the planet's interior. On Earth, compositional diversity in volcanic rocks is closely linked to plate tectonics. Subduction zones, where one tectonic plate dives beneath another, introduce water into the mantle, lowering melting temperatures and promoting the generation of silica-rich magmas. Mars has no plate tectonics, so a different mechanism must be at work.

The researchers propose that the key factor is the longevity of Martian volcanic systems. Because Mars lacks plate tectonics, its volcanic hotspots remain fixed over the same location for billions of years, rather than drifting away as they do on Earth. This means the same volume of mantle is repeatedly heated and partially melted over extraordinarily long timescales.

Over billions of years, this repeated processing could gradually enrich the source region in silica and other incompatible elements, eventually producing the evolved compositions observed in the youngest volcanic deposits. In essence, Mars compensates for its lack of plate tectonics with an abundance of time.

The Water Connection

Another factor that may contribute to compositional diversity is water. While Mars's surface is currently dry, substantial evidence suggests that water ice exists in the subsurface, particularly at mid and high latitudes. If rising magma encounters subsurface ice, the resulting interaction could alter the magma's composition and dramatically change the style of eruption.

Magma-ice interactions are well documented on Earth, particularly in Iceland, and produce distinctive volcanic landforms. The research team has identified several features in Elysium Planitia that closely resemble terrestrial rootless cones and tuff rings, both products of explosive magma-water interactions.

If confirmed, this would have profound implications for the search for habitable environments on Mars. Volcanic heat interacting with subsurface water could create warm, chemically rich niches capable of supporting microbial life, potentially within the geologically recent past.

Implications for Mars Exploration

The revised understanding of Martian volcanism has direct implications for future exploration missions. Sites of recent, compositionally diverse volcanism are scientifically valuable targets because they provide windows into the planet's deep interior and potentially into environments where life-supporting conditions may have existed.

The Elysium Planitia region is already of interest to mission planners. The InSight lander, which operated in the region from 2018 to 2022, detected marsquakes that confirmed ongoing tectonic and possibly volcanic activity beneath the surface. The new volcanic diversity findings add urgency to proposals for follow-up missions with capabilities for direct rock analysis.

A rover equipped with instruments for detailed chemical and mineralogical analysis could resolve many of the questions raised by the orbital data. Are the silica-rich compositions truly dacitic, or could they represent other processes such as weathering or impact alteration? Do the young volcanic deposits contain minerals formed in the presence of water? Are there biosignatures preserved in volcanic-hydrothermal deposits?

A Planet Still Geologically Alive

Perhaps the most profound takeaway from this research is that Mars is not the dead, geologically dormant world it was once assumed to be. The evidence for recent and compositionally diverse volcanism suggests a planet whose interior retains enough heat to drive volcanic activity into the astronomically recent past, and possibly the present.

This living geology makes Mars a more interesting scientific target than ever, not just as a museum of the solar system's early history, but as a world with ongoing processes that continue to shape its surface and subsurface. The volcanoes of Mars, it turns out, have been telling a far richer story than we knew how to read.