Lava tubes are cave formations found where volcanoes generate surface flows in the western United States, Japan, Italy, Australia, Pacific Ocean islands, and other areas. They vary in size and complexity, from short, straight formations to multi-leveled labyrinths that extend for miles. The largest and most extensive lava tubes discovered to date are in Hawaiʻi, where lava flows can travel more than 80 kilometers (50 miles) from their source. This interactive activity, adapted from The Virtual Lava Tube, by Dave Bunnell, offers a visual tour of lava tubes and their many features.
Basaltic lavas, the most common of the three major lava types, are characterized by two primary flow types: pahoehoe (pronounced "paw-hoey-hoey") and aʻa (pronounced "ah-ah"). As with many volcanological terms, these names are of Hawaiʻian origin. Slow-flowing pahoehoe lava is commonly associated with gentler slopes. A glassy skin forms over its rounded, wrinkly surface when it cools. By contrast, when faster-flowing aʻa lava cools, heat loss is more rapid. Because the lava that continues to flow fractures the cooling crust before it fully hardens, aʻa produces a jagged surface.
Pahoehoe lava produces caves known as lava tubes, which form when lava at the outer edges of a flow channel begins to cool and harden, first along the sides of the flow and then on top of it. Lava in the center of the encasement continues to flow until the generating source stops. Once the last of the flowing lava clears the channel, all that remains is a crusty hollow tube.
Even though lava tubes are formed by volcanic processes and are very different from the more common limestone caves, both cave types contain similar depositional features. In lava tubes, stalactites, stalagmites, and columns all form early in the cooling phase. Secondary mineral deposits, such as gypsum or calcite, may appear later as the by-product of chemical reactions that occur long after the walls have cooled.
Lava tubes, like other caves, provide critical habitats for specialized organisms. For example, troglobites, a name given to various animal species that are adapted to live in total darkness, make their homes in the protected underground passages. Some lava tubes also offer insights into cultural history. Ancient cave writings and drawings suggest that our human ancestors used lava tubes as shelters and burial grounds, as well as for religious ceremonies.
As with limestone caves, lava tubes are especially vulnerable to damage due to vandalism, tourism, and pollution. To ensure their protection, resource management strategies are being instituted and enforced.
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