Comparitive Planetology

Here are summaries of a few brief stories that combine Earth data and elsewhere data to get neat understandings of other worlds

1) Carrizozo Lava Flow (image: Google): Looking at Mars, we keep finding beautify lava flows that stream across the surface and end in sprawling lobes. Pouring over images of the Earth, we find the exact same thing (image left of Carrizozo Lava flow in New Mexico). To try and understand the Mars lava flow, a group of geophysicists set off to Carrizozo to see what they could see.

The talk presented by James Zimbelman started with the written notification, “This presentation has been approved for public release by White Sands Missile Range for unlimited distribution. The White Sands Missile Range Operations Security review was completed on February 25, 2008.” The Carrizozo Lava flow intersects White Sands Missile Range, and that added an interesting twist to trying to do field work. This poor determined researcher and his colleagues, I’m guessing, had to jump through more bureaucratic hops to get their Earth-based data then their Martian data - permission was required to explore the lave on the base, and then further permission was required to publish the research on the lava on the base. Perseverance paid off, however. This is neat piece of work.

In exploring the distal lobe of this 5000 year old lava flow, they found the 75 km long lobe was emplaced on an underlying slope of just 0.2-0.4 degrees. Various researchers have guessed the flow rate was somewhere between 5 to 800 cubic meters per second (a HUGE variation), which leads to an emplacement duration of between 2 months and 2-3 years. It always amazing me how slowly volcanoes can ooze their contents across the land. If you look at modern day Mt Saint Helene’s data you can watch the mountain steadily grow a new bulge over years and years! Not all volcanic processes are fast and explosive.

In the case of the Carrizozo lava flow, it appears that lava tubes slowly oozed their contents in a manner that created a triple terraced structure. Looked at from the side, the lava flow has three stair steps that can be explained via a three different mechanisms. It is possible (but not probably) that the lave just came out in a way that caused this three-layer wedding cake structure. More likely, however, the material either came out with a thin runny emerging first and creating the broad base and then the next two terraces were emplaced on top of the runny layer (after it had solidified), or it came out with a tall central lobe coming out first, and subsequent layers running along the sides creating each of the steps.

Topographically, the lava has many different structures (and plants - the photos he showed allowed the lava to in part be identified by where the most green stuff was located. I don’t think this will be true on Mars, but it is cool nonetheless to see it happen on Earth.) At the end of the lava flow, the material separates into different lobes (Zoom and pan at will in Google Map).

View Larger Map

If you look hard enough, you can see this as three different lobes that are bridged by “break out” lava, just like three streams of flowing water might be bridged by side channels. The break outs are very chaotic (called pahoehoe and pronounced ahoyhoy). There are also pits in the lava that have been partially infilled by other lava. Over all though, the terraces are fairly level in elevation on larger scales. These scientists hiked the whole width of the distal feature (I now know why everyone is skinny!) and mapped the features. Across each lobe, elevations typically varied by a couple meters or less on ~kilometer scales.

Taking this study and applying it to Mars, they find that small shield volcanoes, such as Pavonis Mons, has very similar features: “a low shield at the distal end with broad flat plateaus, lobate margins and topographics lows.” It appears that the Martian feature, like the Earth feature, was emplaced via lava tubes. It is guessed that were one to walk across the Martian feature, they’d find themselves on structure nearly identical (as nearly idebtical as any two geologic features can be) to the New Mexico Lava flow - just minus the plants.

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