Craters of the Moon – Lava Tubes on Earth and Mars?

Field Day 3, Stop 3

Dianne Mollica, Scott Lessor, Josh Sheldon

Lava Flow
1. Imagine you are standing on black lava flow in central Idaho, with the sun beating down on you. If you saw the view above, how would you explain these holes in the ancient flow?

Observations:
You should notice a few things in the photo above. First, there are huge angular blocks sitting at the bottom of what appears to be a hole in the ground. Second, there are what look like tunnels or tubes leaving this hole. And finally, if you look carefully, you can see horizontal lines running along the wall at the far side.

Interpretation:
The hole you see above is part of a lava tube, formed when flowing lava forms a crust on top where it is exposed to cool air, but continues to flow under this crust. Sometimes the crust above collapses while there is still lava flowing and the crust is carried away. Without a crust, this formation is a lava channel. More often, the crust holds and a lava tube is formed. However, with nothing underneath to support it, the crust can collapse later, creating something like what we see above. Finally, notice the horizontal lines. These lines are the different heights at which the lava was flowing through the tube.

Lava Tubes
2. Looking up to the ceiling of one of the lava tubes, we see these formations pointing down at us. What could they be?

Observations:
We see pointy formations hanging attached to the top of the tube at their broad base, with the pointy end hanging down toward us.

Interpretations:
Though these may look a lot like garden variety stalactites, they are not. Usually, stalactites are formed when minerals are absorbed into groundwater and then deposited as that water drips down from a cave roof. In this case, however, the pointy formations were created at almost the same time as the lava tube itself. The hot lava was pulled down by gravity and formed these points that end up looking like stalactites.

Lava Tube
3. Here’s one final view of a lava tube. Notice how big it is compared to the people in the picture. What else do you notice in this photo? How does the sunlight enter the tube? How do explain what you see?

Observations:
Based on the height of the people, we see that this lava tube is between 15 and 22 feet tall. There are some angular blocks of rock in the foreground, and then more again in the background where we see sunlight entering the tube.

Interpretation:
This is a classic example of skylights, or areas where the roof of a lava tube has fallen in, opening the tube to daylight. Lava tubes can play host to very interesting ecosystems, with animals that are specially adapted to living in places with little or no light. Skylights provide the transition from daylight to no light.

Connections to Mars:

Caldera
4. What do you see in this image? What do you think the long line that leads from the top of the caldera (circular depression) to the oval is?

Observations:
Based on the information about how and when the image was taken, we know that the caldera is at the top of a hill/mountain. There are several linear depressions that come together and then run down the hill to the ovular depression that appears above. There is a second example of this pattern on the left side of the hill.

Interpretation:
Like its earthly counterpart, lava put out by volcanoes on Mars may flow in channels downhill from its source. Though in this image there does not appear to be a crust remaining, if the channel were to crust over then there could be a lava tube on Mars. The full caption appears below with the image.


5. These vein-like features are part of an image taken of one side of Olympus Mons, the highest volcano in our solar system. What do you think the vein-like features might be?

Observations:
There appear to be two long raised “lines” that meander slightly, like a fluid running downhill. There are also a number or round depressions in the image.

Interpretation:
Planetary geologists have speculated that the two lines visible in this image are lava tubes running down the side of Olympus Mons. Like their counterparts on Earth, they would have been formed when a hot flowing lava channel was exposed to the cold Martian atmosphere. The channel would have crusted over while continuing to flow, forming the lava tube.

The circular depressions are impact craters that record the landing of meteorites after the formation of the initial land. Notice the small impact crater on the upper impact crater. The full caption appears below with the image.

Caldera
Volcanoes Ceraunius Tholus and Uranius Tholus MGS MOC Release No. MOC2-305, 18 April 2002,
http://www.msss.com/mars_images/moc/news2002/ceraunius/

“Acquired in March 2002, this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) wide angle view shows the martian volcanoes, Ceraunius Tholus (lower) and Uranius Tholus (upper). The presence of impact craters on these volcanoes, particularly on Uranius Tholus; indicates that they are quite ancient and are not active today. The light-toned area on the southeastern face (toward lower right) of Ceraunius Tholus is a remnant of a once more extensive deposit of dust from the global dust storm events that occurred in 2001. The crater at the summit of Ceraunius Tholus is about 25 km (15.5 mi) across. Sunlight illuminates the scene from the lower left.”


NASA/JPL/Malin Space Science Systems / Lava Tubes of Olympus, MGS MOC Release No. MOC2-687, 5 April 2004 http://www.msss.com/mars_images/moc/2004/04/05/

“This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows evidence of two collapsed lava tubes on the southeast flank of the giant martian volcano, Olympus Mons. One runs diagonally across the entire image, the other is shorter and does not extend across the whole image. The shorter one is a series of pits and troughs, rather than a continuous channel. Lava flowed in tubes under the surface; later, the roof of each tube collapsed to form a series of pits and troughs which, in the larger example, eventually coalesced to its present, channel-like form. The image is located near 16.8°N, 132.2°W, and covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.”