Volcano Watch - Eruptions and fires

Release Date:

Lava is not fire. People sometimes talk about lava as fire, as in "fire fountain," "curtain of fire," and "river of fire." Most realize that these and similar terms are misleading and confusing metaphors, but bad habits are hard to break.

Volcanologists are weaning themselves away from using the terms, and they are no longer used by HVO scientists in their publications. Lava is liquid rock, nothing else.

Lava can, however, cause fire. In that sense, the two words are sometimes intertwined. The fire caused by the Mother's Day lava flow at Kilauea is an example. The fire owes its start to hot lava igniting vegetation. The lava didn't need a fire to get going, but the fire needed the lava's heat.

The Pu`u `O`o eruption has caused many fires in the past 19 years, some fairly large but most of them small. The Kupukupu Fire, the name given by Hawai`i Volcanoes National Park to the fire ignited by the Mother's Day lava flow, is the largest of the eruption, burning more than 1,480 hectares (3,660 acres) by June 4. But it is only the latest fire of the eruption. Each time lava enters even the tiniest vegetated kipuka, a fire is generated.

Old-timers will recall the heroic efforts of the park to save the Naulu Forest and picnic area during the Mauna Ulu eruption in 1970-1972. Most of this forest, consisting almost entirely of native vegetation, eventually succumbed to the lava flows that spread downslope near and east of the Kealakomo shelter and overlook. The largest fire burned 1,300 hectares (3,200 acres) in 1972, but an earlier fire in 1970 took the real jewels. It was a sad day, indeed, when a large `ulu (breadfruit) tree, a landmark to those driving down the new Chain of Craters Road, was caught by the fire near the base of Holei Pali in 1970. Sad, perhaps, but perfectly natural. Lava has been starting fires since there was vegetation to light.

Recent investigation into the past 1,500 years of Kilauea's eruptive history has uncovered evidence for a number of fires in the relatively dry area between the Hilina Pali Road and the Mauna Ulu lava flows. Some of these fires were almost certainly caused by lava flows, because charcoal is found directly under a flow or in a tree mold formed in a flow.

Other old fires, however, have no certain cause, yet circumstantial evidence suggests a lava origin. For example, lots of charcoal in alluvial debris has radiocarbon ages from the 13th, 14th, and 15th centuries. This was a time when lava flows were frequently erupting from the summit and upper east rift zone of Kilauea. The charcoal is found in deposits on top of, or beyond the ends of, these flows, so we can't really relate it to a particular flow or even to any eruption at all. Nonetheless, it is a logical inference that lava started the fires.

There is even 1,300-year-old charcoal sitting near the ground surface and indicating an old fire possibly ignited by an explosive eruption of about that age.

Fire is just one of many indirect consequences of eruptions. There are others that don't involve fire. For example, many readers will remember the problems at Kilauea 10-15 years ago with acid rain from vog leaching lead out of paint and solder. On a similar note, the upper part of the Ka`u Desert is largely an acid rain desert, caused indirectly by sulfur dioxide emitted in Halemaumau. At other volcanoes, mudflows are commonly disastrous indirect results of an eruption, although they can be direct as well. Volcanic ash can down high-flying jetliners that enter nearly invisible ash concentrations before they know it. On a larger scale, crop failures and short-term weather change can be consequences of very large eruptions.

The Kupukupu Fire reminds us again that eruptions may pose significant problems above and beyond the area actually covered by lava or ash. The earth is a complex system, and even minor natural perturbations in that system can have indirect, often unexpected results.

Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. The "Mother's Day" lava flow is slowly advancing in the flats between Pulama pali and Paliuli with the distal end of the flow located 1.6 km (1 mi) above the Chain of Craters road. The two flows emanating from the "rootless" shields continue to be active. The lower flow along the National Park-Royal Gardens boundary is inflating and spreading on the coastal flats with only minimal movement toward the ocean. The higher flow that entered the top of Royal Gardens subdivision last week has one lobe moving down Prince past Pakalana and another between Prince and Royal approaching Pikake. At least four houses are in the probable path of the flow.

There were no earthquakes reported felt during the week ending on June 6.