Lava Tubes – Formation, Facts, Safety

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Lava Tubes Definition and Formation

Lava tubes or pyroducts are natural tunnels formed by flowing lava beneath the Earth’s surface. They are a common volcanic feature near shield volcanoes, which erupt low-viscosity basaltic lava. Some lava tubes are vast and elaborate, sometimes extending for miles. They are not only geological wonders, but also hold cultural and scientific significance.

Key Points about Lava Tubes

  • Natural Conduits: Lava tubes form when flowing lava cools on the surface while remaining molten underneath, creating hollow tunnels.
  • Variety of Formations: Lava tubes contain unique speleothems, such as lavacicles and driblet stalactites, formed by dripping lava.
  • Global Occurrence: They occur in volcanic regions worldwide, with famous examples in Hawaii, Australia, and the Canary Islands.
  • Extraterrestrial Presence: Lava tubes also occur on the Moon and Mars, offering potential sites for future exploration and habitation.
  • Cultural Importance: Lava tubes hold significant spiritual and historical value for many cultures, particularly as as shelters and sacred sites.

What Is a Lava Tube?

A lava tube or pyroduct is a natural conduit through which lava once flowed beneath the surface of a lava field. These tubes form when the outer surface of a lava flow cools and hardens, while the interior remains molten and continues flowing. As the lava drains away, it leaves behind a hollow, cave-like structure.

How Lava Tubes Form

The formation of lava tubes follows a multi-step process, influenced by the viscosity of the lava, the slope of the land, and the surrounding environment. Here’s a step-by-step breakdown:

  1. Lava Flow Initiation: Lava tubes begin with an eruption from a shield volcano. Low-viscosity basaltic lava flows over the surface, often in a long, steady stream.
  2. Crust Formation: As lava flows, the surface layer cools and solidifies due to exposure to the air. This creates an insulating crust that helps retain heat within the flow, keeping the underlying lava molten.
  3. Tube Formation: The still-molten lava continues flowing beneath the crust. Over time, the lava carves out a tunnel by melting or moving through soft rock, gradually forming a hollow tube.
  4. Drainage of Lava: When the lava supply diminishes, the molten lava within the tube flows out, leaving a hollow conduit. This tube sometimes remains intact as a cave, protected by the insulating crust that formed on top.
  5. Speleothem Formation: In some lava tubes, secondary formations known as speleothems develop. These include features such as lavacicles (lava stalactites), which form from dripping molten rock, or flowstone-like features created by cooling lava flows along the walls.

Characteristics and Features of Lava Tubes

Lava tubes exhibit distinctive characteristics that reflect their volcanic origins. Here are some key features:

  • Types of Volcanoes and Lava: Lava tubes typically form in shield volcanoes, like those in Hawaii and Iceland, due to the fluidity of basaltic lava. Basaltic lava has a low viscosity, allowing it to flow long distances before cooling. The tubes also form around cinder cones during the initial eruption phase and around fissure volcanoes, when the lava is basaltic and fluid. While they sometimes occur, they are less common around stratovolcanoes and lava domes because they produce more viscous lava.
  • Shapes and Sizes: Lava tubes vary widely in size, from narrow passageways to enormous caverns. Tube dimensions depend on the volume and flow rate of the lava. Some tubes are tall enough to walk through, while others can be several meters wide and kilometers long. For example, the Kazumura Cave on Hawaii’s Big Island extends for over 40 miles.
  • Speleothems in Lava Tubes: Common speleothems in lava tubes include lavacicles, which resemble icicles but form from dripping lava, and driblet stalactites, which are smaller, knobby formations. Some lava tubes can also features like flowstone and benches, which are flat shelves formed along the walls.
  • Textures and Surfaces: Inside lava tubes, the walls can be smooth or display ropy textures known as pāhoehoe, which occur when lava cools into smooth, billowy shapes. Some tubes contain jagged surfaces formed by cooling and fracturing.

Lava Tube Ecology

Lava tubes offer a unique and often extreme environment for various forms of life. Despite the harsh conditions, they support distinct ecological communities that have adapted to the darkness, stable temperatures, and nutrient-poor environment. Here’s a look at the fascinating ecology of lava tubes:

Primary Producers

  • Chemoautotrophic Bacteria: In the absence of sunlight, photosynthesis is not possible. Instead, some bacteria within lava tubes derive energy from chemical reactions with minerals in the rocks, a process known as chemosynthesis. These bacteria form the base of the food web and provide energy to other organisms.
  • Fungal Mats: Fungi colonize the surfaces of lava tubes, often forming dense mats. They play a crucial role in nutrient recycling, breaking down organic material that enters the tube from the surface.

Decomposers and Detritivores

  • Microorganisms: Organic matter falls into the tube or washes in with water. A wide range of bacteria and fungi act as decomposers within lava tubes, breaking down organic material.
  • Springtails and Mites: These tiny arthropods thrive in the nutrient-poor conditions by feeding on decomposing matter and microbial mats. They are crucial for the breakdown and cycling of nutrients within the ecosystem.

Trogloxenes, Troglophiles, and Troglobites

  • Trogloxenes (Occasional Visitors): Animals like bats and birds often use lava tubes as shelters but do not spend their entire lives there. Bats, in particular, are important for nutrient input. Their droppings, or guano, provide an essential nutrient source for other organisms within the tube.
  • Troglophiles (Partial Residents): These are species that can live both inside and outside of the tube. Examples include spiders, crickets, and beetles, which enter lava tubes to escape extreme surface conditions or to hunt prey that has wandered inside.
  • Troglobites (Permanent Inhabitants): These specialized creatures have adapted to live exclusively in dark cave environments. Examples in lava tubes include unique species of blind cave spiders and millipedes. Troglobites often display adaptations like reduced pigmentation, elongated limbs, and heightened non-visual senses, such as touch and smell.

Unique Adaptations to the Lava Tube Environment

  • Darkness and Low Light: Organisms in lava tubes adapt to total darkness by relying on non-visual senses. Many lava tube species are eyeless or have underdeveloped eyes. Instead, they rely on tactile or chemical senses to navigate and find food.
  • Stable Temperatures: Lava tubes maintain relatively constant temperatures year-round. This stability allows species that are sensitive to temperature fluctuations, like certain fungi and invertebrates, to thrive.
  • Low Nutrient Availability: The nutrient-poor environment of lava tubes means that organisms must be highly efficient in their use of energy. Many organisms have slow metabolisms and reproduce infrequently due to limited resources.

Ecological Importance of Lava Tubes

  • Refuges for Rare Species: Lava tubes often host endemic species found nowhere else, making them important for biodiversity conservation. These isolated ecosystems act as refuges for species that may have been more widespread in ancient times.
  • Nutrient Cycling: Bats and other trogloxenes play a significant role in the nutrient cycling within lava tubes by bringing in nutrients from the surface. Decomposers then recycle these nutrients, which supports the rest of the ecosystem.
  • Biological Indicators: The unique and sensitive communities in lava tubes act as indicators of environmental health. Changes in the presence or abundance of certain species can reflect broader ecological changes above ground.

Threats and Conservation

  • Human Impact: Human activity disrupts the delicate ecosystems within lava tubes. Direct damage from trampling, graffiti, and littering harm both the physical structure of lava tubes and the organisms living within them.
  • Climate Change: Changes in temperature and humidity disrupt the stable environment that lava tube organisms rely on. Additionally, alterations in surface ecosystems affect nutrient availability within the tubes.
  • Conservation Efforts: Protecting lava tubes often involves restricting access to sensitive areas, particularly in lava tubes with rare or endangered species. Some lava tubes are protected within national parks or conservation areas, which helps to mitigate human impact.

Where to See Lava Tubes

Lava tubes occurs in volcanic regions worldwide. Here are some famous lava tubes:

  • Thurston Lava Tube (Hawai’i, USA): Located in Hawai’i Volcanoes National Park, this tube is easily accessible and provides a glimpse into the island’s volcanic past.
  • Ape Cave (Washington, USA): Formed by the basaltic lava flows from Mount St. Helens approximately 2,000 years ago, Ape Cave is one of the longest lava tubes in North America.
  • Undara Lava Tubes (Queensland, Australia): Created by a volcanic eruption over 190,000 years ago, these tubes are part of the Undara Volcanic National Park and are among the longest in the world.
  • Cueva de los Verdes (Lanzarote, Canary Islands): Part of the longest lava tube in the world, this tube stretches over 8 kilometers and has sections that extend under the sea.

Are Lava Tubes Safe?

Obviously, a hot lava tube is an unsafe place! One of the hazards of walking or driving near a recent lava flow is the risk of breaking into a lava tube, not just because of the heat, but also because of the jagged rocks and and a potential fall risk.

Once a lava tube cools, exploration is reasonably safe, with some caveats:

  • Follow safety tips.
  • Follow the rules. Don’t explore off-limits areas.
  • Use special care in areas featuring “skylights”. These are sections where the tube has broken open to the sky. The area is unstable and there is a risk of additional falling rock.

Safety Tips for Exploring Lava Tubes

Take precautions for safe lava tube exploration:

  • Wear Proper Gear: Helmets, sturdy boots, and headlamps are essential for navigating uneven surfaces and avoid injury from low ceilings and sharp rocks. Wear long-sleeve shirts and long pants. Lava tubes are sometimes much colder than the outside area.
  • Check for Hazards: Some tubes contain loose rocks, slippery surfaces, or steep drops, so proceed with caution. Watch for signs of flooding, as tubes sometimes fill with water during heavy rains.
  • Stay on Marked Paths: In protected areas, stick to designated trails to avoid damaging fragile formations and to ensure your safety.
  • Be Aware of Air Quality: Some tubes can have poor air quality, with low oxygen or high levels of gases like carbon dioxide. Avoid tight, enclosed spaces and know the exit route.

Are There Dangerous Animals in Lava Tubes?

The biodiversity inside lava tubes is usually low, but certain animals that live or shelter within the tubes pose dangers. For example, some tubes contain:

  • Bats: Bats are common inhabitants of lava tubes. While most bats are harmless and avoid humans, they can pose a health risk if they feel threatened and bite. Some species carry diseases like rabies, and their guano (droppings) can harbor Histoplasma spores, which cause histoplasmosis, a respiratory infection.
  • Venomous Spiders: Certain spiders, including potentially venomous species, may live in lava tubes. In Hawaii, for example, there are cave-adapted wolf spiders, which are generally harmless. However, depending on the location, spiders like black widows or recluse spiders might occasionally be found in the entrance areas of lava tubes where they can find prey. These spiders avoid human contact but may bite if disturbed.
  • Centipedes and Millipedes: Some lava tubes host large centipedes, such as the giant centipedes found in Hawaii. These centipedes can deliver a painful bite with venom that, while not typically life-threatening to humans, can cause significant discomfort and, in rare cases, allergic reactions. Millipedes, while not venomous, emit noxious chemicals as a defense mechanism. In confined spaces like lava tubes, these chemicals can cause skin irritation or respiratory discomfort.
  • Rodents: Rodents may shelter in lava tubes, especially near the entrances. While not inherently dangerous, rodents can carry diseases, such as hantavirus or leptospirosis. Rodents also attract predators, which might pose a risk.
  • Snakes: Although rare, snakes might enter lava tubes to hunt for food or seek shelter. Venomous snakes, depending on the region, could potentially be present. However, this is not common due to the generally low prey availability in lava tubes.

Extraterrestrial Lava Tubes

Lava tubes are not limited to Earth; they have also been discovered on the Moon, Mars, and possibly other celestial bodies. The lower gravity and lack of erosion on these planets mean that extraterrestrial lava tubes could be much larger than those on Earth.

  • Moon: Lunar lava tubes are believed to be hundreds of meters wide, potentially large enough to house entire colonies for future lunar bases. The Marius Hills region is one area where researchers have identified possible lava tubes.
  • Mars: Mars has numerous shield volcanoes, such as Olympus Mons, which likely contain extensive lava tube networks. These tubes could provide shelter for future human explorers, as they offer natural protection from radiation and extreme temperatures.

Cultural Significance of Lava Tubes

Lava tubes have been culturally significant for many indigenous groups, who have used them as shelters, burial sites, or spiritual places. For example, Native Hawaiians regard certain lava tubes as sacred spaces linked to their ancestors and deities. In many cultures, lava tubes are considered gateways to the underworld or places of ancient myth and legend.

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