Modified Martian Lava Tubes as Habitats

Submitted to "Case For Mars - 1996"
By R. D. "Gus" Frederick
Member: Oregon L5 Society

Abstract:

One of the key elements for successful long-term human occupation of Mars, is a viable habitation scheme. Countless ideas have been proposed along these lines from converted landers to inflatable domes. The advantages of most schemes thus far are that they are location independent, to an extent. The lander lands and the habitation is set up. In other words, bring the habitat to Mars.

But what if ready-made habitats were available? Select locations on the planet, which with minor modifications, would easily serve as a semi-permanent base of operations? These locations could well be lava tubes.

Lava tubes are caves formed by flows of highly fluid lava--a "river" of molten rock flowing from an eruption source, either volcano or fissure. Often as the flow progresses, the tops and sides solidify. If the flow source stops, the remaining lava may pour out, leaving a hollow "tube" of rock. Not all lava flows produce tubes. Sometimes the flow sides form large "levees" as the sides harden, and the top remains liquid.

On the Earth, the author has personally visited lava tubes on the flanks of Mount St. Helens, in Washington state, the Big Island of Hawaii as well as tubes formed by fissure eruptions in Iceland. Many of the lava flows identified on the planet Mars feature the same characteristics as terrestrial flows, including lava tubes and levees. The main difference is a matter of scale: The Martian features dramatically dwarf their Earth-based counterparts.

This paper offers some speculations on the utilization of these land forms for the construction of viable human habitats. With examples from Ape Cave on Mount St. Helens, and other lava tube-related features here on Earth, I will demonstrate how their much larger Martian versions could provide a quick, easy and inexpensive way to provide long-term human outposts on the Red Planet.

Volcanic Backgrounds:

Growing up in the Pacific Northwest guaranteed a strong exposure to volcanic terrain. My family stressed an appreciation for the great outdoors, so every summer weekend found us bivouacked in any number of remote campgrounds in the High Cascades of Oregon and Southern Washington. A favorite family get-away was the Mount Fuji of North America, Mount St. Helens.

I recall my siblings and I standing at the bottom of steep piles of very fresh-looking pumice overlooking the dark blue waters of Spirit Lake. My dad related how he had read somewhere that a couple of geologists had suggested that Mount St. Helens would erupt in the next twenty years.(1.) Imagine the glee my pre-teen brothers and I expressed as we replied that we hoped it would happen when we were around!

We got our wish in 1980. The very location of that conversation is now occupied by a gaping hole and view of majestic Loowitt's guts. Spirit Lake, while still visible, is radically changed. A reminder of Mother Nature's periodic "rent collections."

Another favorite Frederick family destination was located on the other side of Mount St. Helens along the south slopes. Here, some two thousand years earlier, massive fluid flows of pahoehoe lava spilled from the flanks of this Cascade cone. It is within these flows that the longest and best preserved lava tube systems in the U.S. are located.

Liquid basalt, heated to more than 1200 degrees C, issued from fissures along the sides of Mount St. Helens. Flowing like a river down hill, it followed the path of least resistance, and like wax from a candle, began to freeze along the sides of the flow. The farther from the vent, the cooler the flow became. A crust soon developed over the top of the flow, which tended to insulate the liquid within as it continued downhill.

When the source of magma was exhausted, the remaining liquid lava drained out of the flow, leaving a series of hollow rock tubes to mark its path. Where the crust was too thin, the top of the tube collapsed creating skylight sinkholes. These would provide the future entrances for later human visitation.

The youth of these tubes is the reason that they are so well preserved, as many terrestrial tubes succumb to erosion, earthquakes and sedimentation. Ape Cave, the longest and most famous of the St. Helens lava tubes, traverses a total of 3,904 meters, (12,810 ft.). In many places within the tube, the ceiling is over 7 m tall, and the cave resembles a subway tunnel in places with its smooth, symmetrical meanderings.

I often wondered what it would be like to live in one of these tubes. Dark, damp and cool, but in many ways, a perfect shelter. Of course the occasional chunk of falling ceiling could ruin one's day.

Years later while serving in the U.S. Navy, I found myself in Iceland, stationed at the Naval Station in Keflavic. During a tour of the country side, I was introduced to the Icelandic lava tubes. Many of these were much larger than the St. Helens flows. In fact, one, "Surtshellir," was used in the 17th century as a hide-out for a band of marauding bandits. These tubes were the result of floods of basalt that erupted from fissures, or cracks in the Earth's crust.

Eruption of Martian Data:

After Mount St. Helens came back to life, and the data from Mars started to accumulate, I was drawn to the vast volcanic areas of the Red Planet. The orbital views showed many of the same igneous landforms found here on Earth, with the difference being a matter of scale. The Martian features were much larger, and this included the lava flows and presumably the lava tubes as well.

The tubes are there, many being identified from the "skylights" of their collapsed ceilings. These tubes are considerably bigger than their terrestrial counterparts. Since we have yet to explore the tubes of Mars, we can only assume the their internal structure would be similar to their Earth cousins.

The West flank of Olympus-Mons for example exhibits many landforms that look like collapsed tube skylights. (VO Frame 47B25; 21N, 130W)

Along the Southeast flank of Arsia Mons, a series of well-defined tubes and channels are also visible, (VO Frame 52A04; 12S, 120W) as well as the sides of the Northern shield Alba Patera. (VO Frames 7B94; 41N, 109W and 7B53; 46N, 119W)

The relative elevation may eventually be a factor in locating this tube systems for future habitation. These range from the "low" 1 km of the Northern Alba Patera area upwards to 10 km and greater on the Tharsis shields. An elevation of "0 km" was defined as that elevation where mean atmospheric pressure at the surface is equivalent to the triple-point pressure of water, or 6.1 mbars. (2.) By comparison, my barometer here in Silverton, Oregon is at this moment reading 29.78 mbars. Silverton is at about 200 feet above sea level.

Logic dictates that many of the common features of terrestrial lava tubes would also be present in larger versions on Mars. What we would have would be long tubes of solid rock. It would be a relatively simple matter to build a colony in one of these tubes. It would be air-tight and would offer superior shielding against the raw environment of the Martian surface--its thin atmosphere and resulting exposure to the elements--solar flares, radiation, cosmic rays and the like.

In the second volume of his trilogy of the colonization of Mars, "Green Mars," (3.) Kim Stanley Robinson located one of his rebel colonist groups within a hypothetical modified lava tube situated in the Martian Southern hemisphere, approximately 64S, 290W, in the Northern Dorsa Brevia region. In his scenario, the colonists blocked off sections of the huge tube with bulkheads of a pliable, air-tight fabric.

A small dome was erected over one of the skylights to admit light, and the tube was partially flooded, creating a landscape of underground forests, fields, lakes and islands within this enclosed world. Expansion of the colony was achieved simply by moving deeper into the tube system. He sized his tubes using a 2-to-1 ratio created by the gravitational and other uniquely Martian conditions. NASA observations put the ratio at 10-to-1.(4.)

His tube was wider than it's Earth kin by a factor of several hundred, and was 40 km long. This scheme closed off 12 km of the lava tube, divided into 1 km segments.

Robinson's tube system was apparently from a single flow. It featured only one main (albeit large) single tube. On Earth, and presumably on Mars too, multiple lava flows overlap each other, (5.) sometimes creating lava tubes on top of older lava tubes.

In Ape Cave, this phenomenon is present. In fact, one such area is like a large "bubble" located above the main tunnel. By clambering up a side channel, and crawling through a narrow half meter-high opening for about 3 meters, one enters into a large domed chamber about 7 m in diameter and some 5 m high.

Another aspect of the Earth tubes, is that they tend to collect water. In fact, all of the lava tubes I have explored on Mount St. Helens have small pools of water at their ends. One tube is named "Lake Cave" for the large "lake" that fills the end of it. Another, "Little Red River Cave," has a small stream running through its length. Of course, one also finds fine sandy floors of volcanic ash in places from the various "lahar" or mud-flows that have spilled down the mountain over the years.

The Icelandic tubes I explored tended to have little siltation. This no doubt being due to the fact that they were caused by fissure eruptions that tend towards flood basalts. They did however have water, in some cases forming spectacular ice formations, (left) The Cascade volcanoes including St. Helens are composite cones that mainly erupt silica-rich rhyolites as ash. The fluid basalt flows are few and far between by comparison. Most of the lava tubes that result from the rare pahoehoe flows are soon filled in by later ash eruptions.

On Mars, we may also find water frozen at the end of the tubes. These may in fact be huge natural cisterns. The tubes may well prove to be a good place to look for water. But where to look for the lava tubes? Robinson's Tube Colony was located in the ancient southern flows. I would guess that the younger flows of the Tharsis plateau would be a better place to look. The most easily identifiable tube structures around the great shield volcanoes would make the best candidates.

Building in the proximity of a skylight would allow for the "piping" of sunlight into the tube chamber. Robinson's inflatable bulkheads could be created to block off large sections. An easier approach may be inflating a single, very large balloon within the hollow. This would be like blowing up a toy balloon within a cup. It would conform to the shape of the space, and provide a quick and easy habitable area.

A Procedure . . .

. . . for setting up such a dwelling might involve the following steps:

  1. Identify likely candidate lava tubes from orbit. Look for a series of skylight pits arranged in a linear pattern along lava flows.

  2. Establish ground contact, and do a preliminary evaluation of candidate tubes.

  3. Prepare the site. This may involve clearing some minor debris from the skylight cave-in.

  4. Install the deflated balloon. It would be constructed of a tough, insulated material. The portion where the skylight fits would be clear or translucent to allow for light transmission.

  5. Setup the balloon for inflation. This could be done either from supplied compressed air, or by the Martian atmosphere, with a "slow pump" sucking in Martian air over an extended period of time. (Plants could be introduced at a point to start converting the carbon dioxide into oxygen.)

  6. Once inflated, we move in! Establish some sort of airlock, setup inter walls and partitions, etc.

  7. Communications antenna and solar power units would be set up outside, with the cables running down into the tube.

Advantages:

  • A large protected habitable space could be set up in a very short period of time, maybe within 24 hours if one used supplied compressed air.

  • The surrounding rock would provide an excellent radiation shield.

  • The lava tubes might contain frozen water deposits.

  • By deflating and moving on to other lava tubes, the colony could be semi-portable.

Disadvantages:

  • Location-specific. The scheme would rely on the location of large lava tubes. This would exclude the majority of the surface.

  • Lighting might be a problem. Locating directly under a skylight would help, but usually these areas (in terrestrial tubes) contain huge mounds of debris from the cave-ins that created the skylights.

  • No Martian lava tubes have been explored, so we can only guess at this point as to their viability as shelters. I think it would be a good guess!

There you have my flight of fancy. As I said at the onset, I do not pretend to fully understand all the intricacies of setting up a viable habitat on another world. But then again, you never know when some crazy half-baked idea might prove useful some distant day!

Thank you for taking the time to read this paper.

R. D. "Gus" Frederick
401 Silver Street
Silverton, Oregon 97381
503-873-6216
[email protected]

Author's Biography: Oregon native Gus Frederick, (DOB 10/4/54) lives in Silverton, Oregon with his 14 year-old daughter Genevieve. He works as Instructional Technology Specialist for the Oregon Public Education Network, is a member of the Oregon L5 Society, longtime Mars enthusiast and amateur spelunker, writes science fiction in his free time and collects 78rpm jazz records for fun.

References:

  1. Mullineaux, Donald R. and Crandell, Donald R., 1962. "Recent lahars from Mount St. Helens, Washington" Geological Society of America Bulletin 73, 855-869.
  2. Batson, R.M., Bridges, P.M. and Inge, J.L., 1979. "Atlas of Mars" NASA SP-438, Appendix C: Contour Mapping by Sherman S.C. Wu, 131.
  3. Robinson, Kim Stanley, 1994. "Green Mars" Trade Edition, Bantam Books. Part 6 - Tariqat, 282-284
  4. Viking Orbiter Imaging Team, 1980. "Viking Orbiter Views of Mars" NASA SP-441, 47-61
  5. Williams, Howel and McBirney, Alexander R., 1979. "Volcanology" Freeman, Cooper & Co. Chapter 5, 106-109

Photographs by the Author:

Ape Cave Main Entrance
Mt. St. Helens, Washington, USA

Raufarhólshellir Lava Tube Cave Ice Formations
Southwestern Iceland