How lava flows on Olympus Mons tell us about the volcanic history of Mars

When we think about big mountains on Earth, the first thing that comes to mind is almost always Mt. Everest. Everest, however, is absolutely miniscule in comparison to the solar system’s largest volcano, Olympus Mons.

Standing at 21,229 meters above the Mars global datum (which can be thought of like sea level here on Earth), Olympus Mons is about two and half times as tall as Mount Everest. Unlike Everest, which is the result of two continental plates slamming into each other, Olympus Mons has a volcanic origin. It can be classified as a shield volcano, similar to those that make up the Hawaiian Islands.

Shield volcanoes are characterized by broad, gentle slopes (4-8 degrees) and tend to erupt nonviolently out of fissures on the flanks of the volcano (think the recent lava flows in Hawaii). The tops of shield volcanoes tend to have calderas, which are large collapsed structures found at the top of volcanoes. The magma in the chamber provides pressure that effectively holds up the top of the volcano.The magma chamber is literally inflating the top of the volcano, sustaining its dome-like shape. When the volcano is done erupting and the chamber is partially empty, the top of the volcano collapses and forms a caldera. Things can get a bit more complicated, however, as has been recently discovered at the caldera at the top of Olympus Mons.

Figure 1: The caldera atop Olympus Mons. Colors correspond to elevation, where warmer colors are higher and cooler colors are lower. The blue shapes extending outwards in almost all directions are lava flows. From Mouginis-Mark and Wilson (2019).

The caldera atop Olympus Mons, like the volcano itself, is huge. Its horizontal dimensions are 60 X 80 km, and it has a depth of about 3 km. Lava flows radiate outwards from the rim of the caldera (Fig.1). The strange thing about this caldera, however, is that some of these lava flows appear to flow uphill (Fig. 2). This is not normal, even on Mars. Lava can sometimes travel small distances uphill due to confining pressure or momentum. The lava flow on Olympus Mons, however, didn’t travel a short distance uphill -- it appears to have gone several kilometers!

Figure 2: Zoomed in from figure 1 to show the anomalous lava flow. The left and right images show the same lava flow. The left is CTX image of the flow and the right is an interpreted sketch of the flow with contour lines. The arrow denotes flow direction. Notice how the flow travels uphill. From Mouginis-Mark and Wilson (2019).

Scientists have instead interpreted this to mean that the lava flow was emplaced and flowed downhill normally, cooling as it did so. Later, new magma was brought up to the near surface through cracks in the rock in a sheet-like intrusion, called a dike. This dike caused a localized inflation to occur within the caldera which tilted certain areas. One of those areas was near the lava flow, making it appear to be flowing uphill. But why is this significant? This tilting shows scientists that volcanism didn’t end when previously thought, when the caldera collapse occurred. Instead, there must have been renewed volcanism closer to the present. By understanding the timing of volcanism on Mars, we can better understand Mars’s evolution as a planet, and therefore what past conditions on Mars could have been like. Was Mars more volcanic in its past? Could this volcanism provide a greenhouse effect to allow life to exist? This work takes us one step closer to fully answering these questions.

Original paper:

Mouginis-Mark, P. J., & Wilson, L. (2019). Late-stage intrusive activity at Olympus Mons, Mars: Summit inflation and giant dike formation. Icarus, 319(September 2018), 459–469. https://doi.org/https://doi.org/10.1016/j.icarus.2018.09.038

NASA Cassini Spacecraft Discovered Ingredients That Could Sustain Life on One of Saturn’s Moons

Fig. 1. Enhanced image taken of Saturn’s moon Enceladus showing the erupting geyser spray of fine particles that the Cassini spacecraft flew through. (NASA/JPL)

Evidence is mounting that Saturn’s ice-covered moon Enceladus may be able to support microscopic life. NASA’s Cassini spacecraft flew through an erupting geyser on Enceladus (Fig. 1) and detected large amounts of molecular hydrogen, or H₂. This chemical signature is the critical ingredient needed to support a chemical reaction that feeds certain microbes on Earth (Fig. 2), called methanogenisis. Methanogenisis produces methane from hydrogen and water and creates usable energy for the microorganisms.

Fig. 2. Electron microscope image of methanogens. Methanogens are microbes that get their chemical energy from a reaction that makes methane from hydrogen and water. Recent discoveries from NASA suggest that Enceladus may be able to support such life (Maryland Astrobiology Consortium, NASA, and STSci)

This discovery also reveals information about what the subsurface environments on Enceladus could look like.  According to a recent Science article by NASA scientists (Waite et al., 2017), the detection of H₂ is most plausibly caused by ongoing water-rock hydrothermal reactions at Enceladus’ seafloor (Fig. 3). In such a scenario, hot fluids would flow over and through cracks in rocks releasing H₂ into the overlying ocean. Hydrothermal vents on Earth host massive communities of simple life forms, further strengthening the idea that Enceladus is ripe for life.

Fig. 3. Graphic illustration of the hydrothermal reactions that NASA scientists think are occurring at the bottom of the ocean of Enceladus, producing H₂ (NASA/JPL)

H₂ will only form under specific environmental conditions. Therefore scientists can also infer that the pH ranges of Enceladus’ subsurface ocean are likely fairly basic, ~9-11 (Fig. 4).

Fig. 4. Graphic illustration of what scientists expect the environmental conditions of Enceladus’ oceans to be. The orange region identifies the H₂ chemical signature detected by the Cassini spacecraft. The dark blue diagonal lines show constant ocean pH values.  The highlighted blue region identifies what pH ranges best coincide with what is expected for Enceladus. (Waite et al., 2017)

In contrast, the most common hydrothermal vents found on Earth are acidic not basic. For example, Figure 5 shows a cloudy acidic plume erupting from a hydrothermal vent in near Guam. However, there are unique hydrothermal systems in Hawaii, specifically the Lōʻihi Seamount that have pH’s similar to the estimates for Enceladus. Therefore, before heading all the way back to Enceladus, NASA scientists are planning to first explore closer to home by sending underwater submarines to the Lōʻihi Seamount. One such research project is the NASA SUBSEA or Systematic Underwater Biogeochemical Science and Exploration Analog project. SUBSEA will explore Lōʻihi this August to September to learn more about how the seamount is capable of supporting life.

Fig. 5. Erupting cloudy plume from a hydrothermal vent near the Island of Guam. (NSF)

The discovery of H₂ doesn’t mean that life currently exists on Enceladus, simply that Enceladus may contain chemical food sources capable of supporting microscopic life. The discovery of H₂ is nonetheless very exciting and makes Enceladus a top choice for future space missions. The discovery of potential microscopic life beyond Earth may soon be within reach.