Lava builds, destroys

The drama playing out in Pahoa is part of a natural process ongoing since before the dawn of civilization.

The Hawaiian Islands are at the southeastern end of a string of volcanoes that began erupting more than 70 million years ago, and each island is made up of one or more volcanoes that emerged from the sea floor over many thousands of years.

Most of the volcanic activity known to man has occurred on Hawaii island, the youngest isle, composed of five volcanoes. Scientists say at least two of them, Kilauea and Mauna Loa, are far from finished.

While most eruptions around the world occur where the Earth’s tectonic plates grind together, the volcanoes here are driven by the Hawaii hot spot deep in the Earth.

The Hawaii hot spot pushes red-hot basaltic magma through the Earth’s crust until it spills onto our landscape as molten rock at 2,100 degrees Fahrenheit, said Janet Babb, spokeswoman for the U.S. Geological Survey’s Hawaiian Volcano Observatory.

Kilauea has been almost completely repaved by molten rock in the past 1,000 years, and scientists said it will be covered over again in the next 1,000.

Since the current eruption began in January 1983, about 50 square miles of Puna have been covered with new lava, a figure representing nearly 10 percent of the surface of Kilauea.

These eruptions occur either at Kilauea’s summit or along its southwest or east rift zones in and around the Puu Oo vent. Most of the recent lava flows have moved in a southerly direction, reaching the ocean about 75 percent of the time.

But the northeastward movement of the current June 27 lava flow is not unprecedented, Babb said. Lava flows also traveled northeast of Puu Oo between 1983 and 1986 and for four months in 2007, as well as during the past 19 months, but they were relatively short-lived events.

No lava flow has gone as far as this one — 13.5 miles as of Tuesday, Babb said.

If the flow continues its march along its same general path, it will reach the ocean in roughly 6 miles.

And if it reaches ocean, the interaction between the hot lava and seawater will create a plume of steam laced with glass fragments and hydrochloric acid, known as laze. Laze is salty, corrosive and unhealthful to humans. It should be avoided, scientists said.

Another thing to avoid is the lava as it passes over vegetated areas. That’s where small "methane" explosions occur from combustible gas pockets in the ground. Such explosions are capable of throwing people several yards.

Flows from Hawaiian eruptions can be divided into two types by their structural characteristics. Pahoehoe and aa, Hawaiian names introduced to science in the early 19th century, are now used by volcanologists to describe similar lava-flow types.

Pahoehoe lava, the type in the current June 27 flow, is a relatively smooth flow that can be billowy or ropelike. It often advances in "toes" or snaking columns. Aa lava flows are denser and more viscous than pahoehoe, and tend to move more slowly.

Pahoehoe flows can form lava tubes when the surface cools and the inside remains hot. Tube-fed flows can move faster and extend over long distances.

The coastal town of Kalapana was destroyed in 1990 by the same type of slow-moving pahoehoe that is threatening Pahoa. Kalapana was buried under 60 feet of lava over a period of six months, during which the flow was plagued by typical fits and starts and an unpredictable path.

Scientists from the Hawaiian Volcano Observatory are capable of predicting whether an eruption is imminent and can forecast the path of a lava flow.

Even so, uncertainty remains due to a variety of factors including subtle variations in topography, changes in lava volume, and where and how lava enters or exits ground cracks along the rift zone, Babb said.

According to University of Hawaii at Hilo volcanology professor Ken Hon, variations in the amount of lava reaching the front of a flow can be caused by hiccups in volcano output or blockages in the lava tube system. Both can cause the flow to pause, creating false hopes that it has ceased, he said.

Over a course of weeks to months, such flows can branch off and change course due to barriers formed from previous flows, making for an unpredictable path.

A flow that at first is narrow and thin and would appear to damage only a few properties can eventually thicken and spread out from new breakouts, destroying nearby structures that were missed originally.

At Kalapana, numerous stops and starts caused the flow to spread out over different paths, covering a wider area and eventually engulfing the entire town, according to Hon.