Hawaiian village's lava menace reminds us: We're all floating on molten rock

Molten lava is on the doorstep of a small town on Hawaii’s Big Island, pouring with an excruciating certainty since the June 27 eruption of the Kilauea volcano.

The lava flow is moving about 10 to 15 yards an hour, according to civil defense authorities who issued an evacuation alert for Pahoa.

Kilauhea has been erupting for more than 30 years, but the lava flow erupted from a new vent and is advancing toward the village’s main street and could cover Highway 130 within two weeks.

Lava is the molten rock that forms inside some planets – including Earth – and flows at about 2,000 degrees Fahrenheit, which is hot enough to melt or burn anything in its path.

Geothermal energy within the Earth heats the rock to liquid state that is up 100,000 times more viscous – or thick and syrupy – than water, which allows lava to flow great distances before it cools and solidifies into igneous rock.

Inside the Earth, molten rock is called magma, and may also contain suspended crystals and volatiles that are released as gas or liquid.

Magma forms in the crust and upper mantle, about 125 miles beneath the surface – although most of the Earth at this depth is solid ultramafic rock.

Rock melts from intense geothermal heat, of course, but low pressure in some areas of the Earth’s mantle and the addition of small amounts of water allows atoms to move freely away from one another.

This partially melted rock is less dense than its parent silicite, and so it tries to rise.

Some of that molten rock reaches the surface as lava, while the rest solidifies on its way up through the Earth’s crust.

The lava erupts through the Earth’s surface at points where rigid tectonic plates – which essentially float above a layer of partially molten rock – move toward or away from one another.

Lava in Hawaii is made up of basalt – a dark-colored, fine-grained igneous rock that underlies most areas of the Earth’s ocean basins and is found beneath more of the Earth’s surface than any other rock type.

Basaltic lava has a relatively low viscosity and bursts through the Earth’s surface in non-explosive eruptions because dissolved gases within the molten rock escape as the magma approaches the surface without building up intense pressure underground.

By comparison, andesitic/rhyolitic lava – such as the type found at the Mount St. Helens eruption – has high viscosity and intense gas pressure, which causes sudden, intense volcanic eruptions.

Low-viscosity lava flows easily and forms puddles and channels as it pours away from the volcano, releasing gas bubbles.

This creates Hawaii’s distinctive loose, broken a’a rock formations or the smooth, undulating formations known as pāhoehoe – which are each created as the lava flow thins and cools.

Gas emissions near Pahoa remain elevated, at 2,700 to 3,600 metric tons, or 6 million to 8 million pounds per day, according to the U.S. Geological Survey's Hawaii Volcano Observatory.

Those gases are mostly sulfuric compounds, but they also can form poisonous acids when they come into contact with water.

The intensely hot lava flow is burning vegetation and man-made objects as it creeps across the terrain, and residents have been asked to gather their belongings and leave the village.

"You know, honestly, it's just material. I came into this world naked, I'm going out naked," resident Alii Hauanio told NBC News. "The memories I can take, and that's what’s the most precious, and that's what I can keep."