In Hawaii, as on Mars, Lava Tubes Hide Secrets Beneath the Surface

By Kate Greene | June 14, 2013 2:52 pm

This is the ninth in a series of reports from the HI-SEAS simulated Mars mission. Read others in the series here.

lava tube Hawaii

The first lava tube we encountered was large but inaccessible without specialized gear. Credit: Kate Greene

Most of our time on this simulated Mars mission is spent inside a geodesic dome. We conduct research, make and document meals for our food study, do chores, and fill out psychological and behavioral surveys. It’s no surprise, then, that adventure is hard to come by.

But on Wednesday of this week, three of us gave it our best shot. We donned our green spacesuit simulators and took a hike. For two and a half hours, we clambered over the shifty and crumbling lava rocks just east of our habitat. We walked to the edges of pits and peered over steep drop-offs. And we investigated a nearby lava tube cave, hollowed out years ago by an immense column of molten lava.

Lava tube skylights

A walkabout such as this is called an EVA, or extra-vehicular activity. Wednesday’s EVA had a particular objective: to explore the caves and cavities near our habitat. Technically called lava tubes and skylights, these structures interest our crew geologist, Oleg Abramov. Back on Earth, Oleg is a research space scientist with the USGS astrogeology branch in Flagstaff, AZ. Here on simulated Mars, he plans and leads geological EVAs.

On this EVA, our longest and most ambitious to date, Oleg’s intent was to collect samples. He wanted to get better acquainted with the geology of the region, including the composition of lavas and white coatings we’ve seen on many rocks in the area. In addition, he wanted to ground-truth satellite images for a number of skylights he spotted on Google Earth/Simulated Mars. His hope was that some of these holes in the ground would provide access to lava tube caves below.

Caves on Mars

NASA’s Mars Reconnaissance Orbiter took this photo of a cave skylight on Pavonis Mons, a large volcano on Mars. The pit is about 180 meters wide.
Credit: NASA/JPL/University of Arizona

Thanks to satellite imagery, we now know that both Mars and the moon also have lava tubes and skylights. These caves and holes likely formed the same way they do on Earth.

As a channel of molten lava flows, its top layer, exposed to air, cools and forms a crust. Below, the hotter lava continues to course until it empties out, leaving behind a tube-like cave. Skylights form when parts of the lava tube ceiling collapse. Sometimes these ceilings crumble and completely block access to the cave. Other times, they fall away clean, leaving pits with dangerous, potentially unstable overhangs. But once in a while, the rocks fall in such a way to give unfettered access to a lava-carved tunnel.

Caves and skylights on Mars and the moon have recently attracted the attention of researchers keen on finding the best places to built extra-terrestrial habitats (as well as those looking for extra-terrestrial — likely microbial — life). Temperatures underground are less variable than on the surface. Moreover, caves protect against radiation; a below-ground habitat wouldn’t need heavy, expensive radiation shielding.

Pit success

But on our EVA this week, we weren’t looking for a new place to live. We just wanted to explore and collect some geological samples. The first pit we approached was an enormous gouge in the ground. Inside, a cave mouth gaped roughly 20 meters high. Unfortunately, the edges of the skylight were simply too dangerous to descend in our bulky spacesuit simulators and without rappelling gear.

The next skylight was smaller, about five meters across, but its perimeter seemed unstable. We couldn’t see a lava tube entrance and could only get close enough to get the sense that the drop would be a doozy. We affectionately called this one the Pit of Death.

entrance of the lava tube

Science officer Yajaira Sierra-Sastre at the entrance of the lava tube. Credit: Kate Greene

After a few more inaccessible skylights, we came upon a fairly shallow one that sported a lava tube opening with surprisingly easy access. Oleg, Yajaira Sierra-Sastre (our science officer), and I made our way with caution. Last September, archaeologists discovered what appeared to be an ancient Hawaiian burial site in a lava tube in an area adjacent to our habitat. Human remains were found, along with a hearth and kukui nut shells. Sensitive to the possibility of disturbing such a site, we stayed near the entrance and looked for indicators of prior human activity. There were none, so Oleg collected samples of white coating on the rocks while Yajaira and I took pictures and video to document the structure.

On the way back to our habitat, we came upon a few more skylights and another death pit. We didn’t dawdle or get too close. Our return journey was slow and mostly consisted of walking on solidified pāhoehoe lava flows. These are the kind that can take on a variety of looks: like heavy fabric that’s bunched and frozen in place, like thick petrified ropes or like piles of shattered dinner plates.

We also made a difficult crossing of an aʻā lava flow, the type that’s sharp, jagged and brittle. And the final challenge between us and our dome was a steep up-and-over on a cinder cone ridge made of small, gravel-like stones. Two steps forward, one step back. After what seemed an eternity on uneven, ankle-breaking terrain, we finally made it home. We arrived safe, sound, and grateful for the chance to explore.

CATEGORIZED UNDER: Mars on Earth, Top posts
  • Natalie Willoughby

    Awesome. Great pictures, too. Sounds like quite an adventure. :)

  • m12345

    Im glad they are coming around to my thinking about an underground base.

    I made mention the first landing craft should be a drill and drill an underground cavern complex, with which the first inhabitants have a shelter. They may not use it from the off, but they can get it operational when they arrive, allowing them to have a secure infrastructure in place for all eventualities.

    Then you can add an above ground complex to it and build a truly inter-locking complex as it grows, with underground tunnel systems connecting areas.

    Local sand would be turned into glass and provide the necessary roofing and building materials where required, and hopefully filled with water such that these viewing spots have maximal protection and also have a water source should it be required. Lots of these viewing tanks could be located around the facilities with dual purposes.

    The glass can be ground into mirrors and telescope designs so that people can just stand under them and view the stars around with out necessarily using a giant telescope.

  • Carl Fago

    I wonder if the safety of being in the earth’s atmosphere allowed more risks to be taken. The lava field can have a number of sharp edges and those suits didn’t look all that robust.

    Glad the experiment is happening! More data to increase the chances of a successful trip to Mars in the future!

  • Jay Dillon

    There is discussion of sending humans to Mars, but if people go there
    even for short stays, they will need a safe place for shelter. An
    underground Mars cave system would be the best way to survive Mars’s
    constant destructive sandstorms and powerful tornadoes. I don’t think
    any spacecraft lander will survive very long on the surface without the
    ability to dig down under the surface to protect itself. Also it should
    be easier to conserve heat below the surface.

    • Thomas

      I agree,going to Mars and trying to live on the surface,would be suicidal,its just too extreme of a environment.The lava tubes ,caves etc will buy us lots of time.


Field Notes

Firsthand reports from DISCOVER correspondents covering science as it happens.

About Kate Greene

Kate Greene is a San Francisco-based science and technology journalist whose work has appeared in Discover magazine, The Economist, and U.S. News & World Report, among others. She is presently a crewmember of HI-SEAS (Hawaiian space Exploration Analog and Simulation), a 120-day simulated Mars mission, during which she will live on the rocky slopes of the Hawaiian volcano Mauna Loa inside a two-story dome, eating astronaut food. As a kid, she wanted to be an astronaut. Gastronaut’s not bad either. Her Internet home is


See More


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Collapse bottom bar