Inside Aden Crater, a World of Tunnels, Tubes and Pits

Inside Aden Crater, a World of Tunnels, Tubes and Pits

(Looking down toward the network of lava tubes from the top of Aden Crater. Photo: Kayla McKiski)

By Nicola Shannon

As the RIS4E team arrived at the base of Aden Crater, jagged clumps of dark, porous rock rolled and crunched under the rubber of their car tires and boots. At Kilbourne Hole, the team’s main field site 10 miles away, the ground underfoot had been all ash and sand. But Aden Crater was something different—a line of huge crumbled pits that ran down the side of the volcano and out into the flat, endless desert.

Nikki Whelley, who works in education and outreach for NASA, reminded the team to wear gaiters and gloves to protect against falling on a sharp rock or one of the many species of cacti. And, maybe, rattlesnakes. They like to hide in the shade under the rocks here. Gaiters might not a lot of use, Whelley said as the group set out, “but they’re better than nothing.”

The team’s research at Aden Crater involved many of the same instruments as at Kilbourne, but the day was structured differently because the mission was more about hard science. Instead of the timed moonwalks, or EVAs, that the team used to test equipment at Kilbourne hole, the researchers were interested in volcanoes and lava flows. Their explorations could reveal small clues about the Earth’s past and maybe about the past and present of other rocky bodies of the solar system.

The team’s research at Aden Crater involved many of the same instruments as at Kilbourne, but the day was structured differently because the mission was more about hard science. Instead of the timed moonwalks, or EVAs, that the team used to test equipment at Kilbourne hole, the researchers were interested in volcanoes and lava flows. Their explorations could reveal small clues about the Earth’s past and maybe about the past and present of other rocky bodies of the solar system.

Aden Crater is actually not a crater, but a small shield volcano, one characterized by lava that spattered and flowed from the center and built up shallow walls when it erupted. While Kilbourne Hole was formed by a massive explosion, resulting in small particles of ash and debris layering around the crater, Aden Crater had liquid lava flows that formed rivers, tubes, pits and other structures in and around the volcano. RIS4E is researching the differences between some of these features on Earth and beyond, focusing particularly on the lava tube.

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Lava usually hits the Earth’s surface at between 1300 and 2400 degrees Fahrenheit and cools very quickly, leaving a crust that new lava flows over, or under. Huge rivers of molten lava can continue to flow even within layers of crust that have hardened around them. These rivers create complicated networks of lava tubes, most of which harden under the ground as the lava stops flowing. Other times, when the river has somewhere to drain, the lava leaves an empty tunnel, like an underground hallway. On Earth, most tubes are around 50 feet wide or less. On the moon, where these rivers, or lunar rilles, were much larger, tunnels can be miles wide.

To volcanologists like Brent Garry, a RIS4E co-investigator from NASA’s Goddard Space Flight Center, the science behind these volcanic processes is fascinating on its own. But NASA is researching lava tunnels on Earth for the possibility that similar hollow tunnels on the moon could be used by future astronauts for protection from dangerous lunar radiation.

The Thurston Lava Tube is a main attraction for visitors of Hawaii Volcanoes National Park.

The Thurston Lava Tube is a main attraction for visitors of Hawaii Volcanoes National Park. (Photo: National Park Service)

The idea of lava tunnels being a kind of fallout shelter on the moon goes back several decades, Garry said. “We just didn’t have the instruments that could get us the resolution to actually search the lunar surface for these things.”

Because the moon has no atmosphere or magnetic field, its surface is exposed to forms of radiation from heavier radioactive elements that we are safe from on Earth. But the intensity of that radiation would also make it harder to block. So even if there is a giant hollow lava tunnel accessible by astronauts on the moon, it might not be a safe haven from all space radiation.

The RIS4E researchers are interested in the possible protective function of lava tunnels for another reason: The perennial question of life on Mars. Jake Bleacher, the geologist who led the RIS4E field team, said that if any life forms did exist on Mars they might have used lava tubes for protection as the environment around them changed.

“We know on Earth that once life gets a foothold it’s very difficult to get rid of life,” Bleacher said. “Life may have retreated to places like lava tubes to continue to survive.”

Back here on Earth, geologists have long been fascinated by these unusual volcanic formations. Pits have usually been discovered in places where the ceiling of a tunnel has caved in, leaving openings like skylights on the surface. But not all pits are openings to tunnels. Sometimes, part of a lava flow has inflated under a hardened surface crust and then collapsed, leaving a pit in the ground that goes straight down but doesn’t connect to a tunnel.

To distinguish some kinds of pits from the surface of the volcanic field, RIS4E used specialized equipment such as a device called a terrestrial laser scanner, a type of LiDAR (Light Detection and Ranging) instrument.  The laser scanner, perched atop a large tripod, was transported around the volcano’s hardened sides by Garry and his LiDAR coworker at Goddard, Patrick Whelley. The two geologists use their LiDar data to make detailed 3D maps of lava tunnels.

Meanwhile, Stephen Scheidt, a RIS4E collaborator from the Lunar and Planetary Laboratory at the University of Arizona, used a drone to create digital images of the volcano that would be used in tandem with the LiDAR data to produce the maps. The high resolution aerial photos are comparable to scans of the moon’s surface taken by satellites.

An image of a possible skylight pit in the Marius Hills, taken by the Lunar Reconnaissance Orbiter Camera. (NASA/Goddard Space Flight Center/Arizona State University)

An image of a possible skylight pit in the Marius Hills, taken by the Lunar Reconnaissance Orbiter Camera. (NASA/Goddard Space Flight Center/Arizona State University)

In these scans, scientists have found multiple deep pits that look like lava pits, or openings to lava tubes. One lunar pit, in the Marius Hills, an area in the western hemisphere of the moon, was labeled a possible skylight to a lava tube after images were taken by Japan Aerospace Exploration Agency’s (JAXA) SELENE lunar orbiter in 2009. Gravitational measurements by NASA’s GRAIL spacecraft and radar sounder scans by JAXA’s SELENE orbiter have also given scientists reason to believe there is a hollow tube, what the lunar scientists call void space, connected to this pit.

Next year, RIS4E will be bringing more geophysical instruments to Aden Crater, like magnetic survey equipment and ground penetrating radar, to pinpoint what types of measurements are needed to detect underground lava tubes from the surface of the Earth.

“Say we figure out that to detect a lava tube on Earth, what we need is good topography maps, some radar, and some magnetometer stuff. Those are the three tools that we need to tell the difference between inflation pits and lava tubes,”Patrick Whelley explained. “Then, we could make a reasonable argument that if you’re sending astronauts to the moon where you think there might be a lava tube, then you have to send these three instruments.”

(Looking down toward the network of lava tubes from the top of Aden Crater. Photo: Kayla McKiski)

By Nicola Shannon

As the RIS4E team arrived at the base of Aden Crater, jagged clumps of dark, porous rock rolled and crunched under the rubber of their car tires and boots. At Kilbourne Hole, the team’s main field site 10 miles away, the ground underfoot had been all ash and sand. But Aden Crater was something different—a line of huge crumbled pits that ran down the side of the volcano and out into the flat, endless desert.

Nikki Whelley, who works in education and outreach for NASA, reminded the team to wear gaiters and gloves to protect against falling on a sharp rock or one of the many species of cacti. And, maybe, rattlesnakes. They like to hide in the shade under the rocks here. Gaiters might not a lot of use, Whelley said as the group set out, “but they’re better than nothing.”

The team’s research at Aden Crater involved many of the same instruments as at Kilbourne, but the day was structured differently because the mission was more about hard science. Instead of the timed moonwalks, or EVAs, that the team used to test equipment at Kilbourne hole, the researchers were interested in volcanoes and lava flows. Their explorations could reveal small clues about the Earth’s past and maybe about the past and present of other rocky bodies of the solar system.

The team’s research at Aden Crater involved many of the same instruments as at Kilbourne, but the day was structured differently because the mission was more about hard science. Instead of the timed moonwalks, or EVAs, that the team used to test equipment at Kilbourne hole, the researchers were interested in volcanoes and lava flows. Their explorations could reveal small clues about the Earth’s past and maybe about the past and present of other rocky bodies of the solar system.

Aden Crater is actually not a crater, but a small shield volcano, one characterized by lava that spattered and flowed from the center and built up shallow walls when it erupted. While Kilbourne Hole was formed by a massive explosion, resulting in small particles of ash and debris layering around the crater, Aden Crater had liquid lava flows that formed rivers, tubes, pits and other structures in and around the volcano. RIS4E is researching the differences between some of these features on Earth and beyond, focusing particularly on the lava tube.

Lava usually hits the Earth’s surface at between 1300 and 2400 degrees Fahrenheit and cools very quickly, leaving a crust that new lava flows over, or under. Huge rivers of molten lava can continue to flow even within layers of crust that have hardened around them. These rivers create complicated networks of lava tubes, most of which harden under the ground as the lava stops flowing. Other times, when the river has somewhere to drain, the lava leaves an empty tunnel, like an underground hallway. On Earth, most tubes are around 50 feet wide or less. On the moon, where these rivers, or lunar rilles, were much larger, tunnels can be miles wide.

To volcanologists like Brent Garry, a RIS4E co-investigator from NASA’s Goddard Space Flight Center, the science behind these volcanic processes is fascinating on its own. But NASA is researching lava tunnels on Earth for the possibility that similar hollow tunnels on the moon could be used by future astronauts for protection from dangerous lunar radiation.

The Thurston Lava Tube is a main attraction for visitors of Hawaii Volcanoes National Park.

The Thurston Lava Tube is a main attraction for visitors of Hawaii Volcanoes National Park. (Photo: National Park Service)

The idea of lava tunnels being a kind of fallout shelter on the moon goes back several decades, Garry said. “We just didn’t have the instruments that could get us the resolution to actually search the lunar surface for these things.”

Because the moon has no atmosphere or magnetic field, its surface is exposed to forms of radiation from heavier radioactive elements that we are safe from on Earth. But the intensity of that radiation would also make it harder to block. So even if there is a giant hollow lava tunnel accessible by astronauts on the moon, it might not be a safe haven from all space radiation.

The RIS4E researchers are interested in the possible protective function of lava tunnels for another reason: The perennial question of life on Mars. Jake Bleacher, the geologist who led the RIS4E field team, said that if any life forms did exist on Mars they might have used lava tubes for protection as the environment around them changed.

“We know on Earth that once life gets a foothold it’s very difficult to get rid of life,” Bleacher said. “Life may have retreated to places like lava tubes to continue to survive.”

Back here on Earth, geologists have long been fascinated by these unusual volcanic formations. Pits have usually been discovered in places where the ceiling of a tunnel has caved in, leaving openings like skylights on the surface. But not all pits are openings to tunnels. Sometimes, part of a lava flow has inflated under a hardened surface crust and then collapsed, leaving a pit in the ground that goes straight down but doesn’t connect to a tunnel.

To distinguish some kinds of pits from the surface of the volcanic field, RIS4E used specialized equipment such as a device called a terrestrial laser scanner, a type of LiDAR (Light Detection and Ranging) instrument.  The laser scanner, perched atop a large tripod, was transported around the volcano’s hardened sides by Garry and his LiDAR coworker at Goddard, Patrick Whelley. The two geologists use their LiDar data to make detailed 3D maps of lava tunnels.

Meanwhile, Stephen Scheidt, a RIS4E collaborator from the Lunar and Planetary Laboratory at the University of Arizona, used a drone to create digital images of the volcano that would be used in tandem with the LiDAR data to produce the maps. The high resolution aerial photos are comparable to scans of the moon’s surface taken by satellites.

An image of a possible skylight pit in the Marius Hills, taken by the Lunar Reconnaissance Orbiter Camera. (NASA/Goddard Space Flight Center/Arizona State University)

An image of a possible skylight pit in the Marius Hills, taken by the Lunar Reconnaissance Orbiter Camera. (NASA/Goddard Space Flight Center/Arizona State University)

In these scans, scientists have found multiple deep pits that look like lava pits, or openings to lava tubes. One lunar pit, in the Marius Hills, an area in the western hemisphere of the moon, was labeled a possible skylight to a lava tube after images were taken by Japan Aerospace Exploration Agency’s (JAXA) SELENE lunar orbiter in 2009. Gravitational measurements by NASA’s GRAIL spacecraft and radar sounder scans by JAXA’s SELENE orbiter have also given scientists reason to believe there is a hollow tube, what the lunar scientists call void space, connected to this pit.

Next year, RIS4E will be bringing more geophysical instruments to Aden Crater, like magnetic survey equipment and ground penetrating radar, to pinpoint what types of measurements are needed to detect underground lava tubes from the surface of the Earth.

“Say we figure out that to detect a lava tube on Earth, what we need is good topography maps, some radar, and some magnetometer stuff. Those are the three tools that we need to tell the difference between inflation pits and lava tubes,”Patrick Whelley explained. “Then, we could make a reasonable argument that if you’re sending astronauts to the moon where you think there might be a lava tube, then you have to send these three instruments.”

Sun, Snakes and Safety


In the field, preparing for risks has its rewards.

Read more