Hawaii is a volcanic playground. Its lava flows meander over their frozen cousins, crumbling into the gloriously named “a’a” formations, or oozing out into stringy, ropy “pahoehoe.” Volcanic deltas collapse and fall into the sea, releasing “lava hoses” into the Pacific Ocean and causing steam explosions.
All the while, the lava lake at the heart of Kilauea bubbles and boils; when it rises over the rim, it forms a “lava curtain”, an incandescent cascade of fire.
As awe-inspiring as these works of volcanic art are, they pale in comparison to lava tubes – natural conduits of molten rock. As portrayed so beautifully in June’s edition of National Geographic magazine, they are found all throughout Hawaii, much like a labyrinth carved out by an ancient serpent.
The science behind these tubes is as remarkable as their beauty. When a lava flow is thick enough, the outside cools faster than the inside, which means the surface crusts over. This crust insulates the lava inside, keeping it molten, and eventually forcing it through nascent channels. When the lava flow drains out into the sea, these channels are left behind.
The dimensions of lava tubes vary considerably, but they can be up to 15 meters (49 feet) wide, and can be found up to 15 meters below the surface. They are invariably long, and some have been known to reach 50 kilometers (31 miles) from start to end.
Walking into the tubes from the seaward end into the core of the island means that you are walking up flow, so to speak – towards the vent or fissure that first birthed the lava. You are walking into the dragon’s cave.
Their ceilings are often decorated with speleothems – cave deposits formed by mineral accumulation. In regular caves, you get stalactites and stalagmites, which take millennia to form. Lava tubes have their very own versions, which some have taken to calling “lavacicles.” These can form in a matter of hours as pressurized lava drips down from the tube’s roof and quickly cools into a glass-like substance.
Sometimes you even get “lava ponds”, areas wherein the glorious fiery gloop accumulates. As it cools, it shrinks, leaving unusually-shaped depressions in the ground. When the roof partly collapses, you get a “skylight”.
You can find lava tubes not just in Hawaii, although this is arguably the best place in the world to find them. Tenerife also has a few, and certain sites across Australia – which was once upon a time an impressively volcanic landscape – are aerated by their own tube networks.
Martian and Lunar lava tubes are also known to exist, but thanks to the planet’s incredibly fluid and superheated lava flows, the longest tubes known to science can be found on Venus.