# Volcano Watch — Lava-flow hazards revisited

Release Date:

Every day at the Hawaiian Volcano Observatory, we scan incoming data from field instruments that will warn of new volcanic activity on the island. Kīlauea, of course, is already erupting. Mauna Loa and Hualalai have both erupted in the not-too-distant past, and each will erupt again in the future.

As more people populate the flanks of these volcanoes, the property losses and disruption caused by future eruptions will increase.

The need to identify the level of hazard led the U.S. Geological Survey to develop the first volcanic hazard-zone map for Hawaii in 1974. The current map, last revised in 1992, divides the island into nine zones based on rates of coverage by past lava flows. Zones 1-3 are limited to the most active volcanoes, Kīlauea and Mauna Loa. Zone 1, the most hazardous, includes the summits and rift zones of these volcanoes, where vents have been repeatedly active in the last 200 years and lava flows will originate in the future. Areas adjacent to and down slope of the rift zones make up zone 2. All 186 houses destroyed in the ongoing eruption of Kīlauea were in zone 2, most about 13 km (8 miles) from the vent.

Information on the lava-flow hazard map is in a booklet entitled, "Volcanic and Seismic Hazards on the Island of Hawaii." This booklet is available at no cost from the Hawaiian Volcano Observatory and can be viewed online at http://pubs.usgs.gov/gip/hazards/hazards.html.

Preparations are underway to produce the next generation of lava-flow hazard maps, based on the probability of lava flow inundation. As with probability maps for flood-prone areas, these maps will give the probability of an area being covered by lava in a given time, say 50 years. Calculating the probability of lava-flow inundation has become possible as detailed digital geologic maps for the island are completed.

Maps showing the probability of lava-flow inundation will provide a more quantitative assessment of the hazard, but the bottom line remains the same: how do we use this information?

Nothing we can presently do will reduce volcanic hazards—;natural events outside of human control. We can, however, reduce risk—;a measure of financial and human costs associated with the occurrence of such events.

The single most important tool for reducing risk from natural disasters, and the one least used, is land-use planning. Hilo has a fine example of land-use planning designed to minimize tsunami damage. A system of state and county parks now occupies low-lying areas severely damaged in the 1946 and 1960 tsunamis. New buildings within this zone must be constructed so that tsunami waves can pass through the ground floor, causing minimal structural damage.

We can dramatically reduce risk in high lava-flow hazard areas by not building or living in these areas or by limiting the density and type of development that can occur there. Hazard information should be a primary consideration in development of public and private infrastructure, such as schools, hospitals, water wells, and power plants.

The biggest problem with implementing such risk management is that over 12,000 people already live in the two highest lava-flow hazard zones. New developments are proposed all the time. Is it realistic for individuals to shoulder their own risks, as some have proposed? Probably not, as they, too, rely on the tax-supported infrastructure. When disasters strike, these individuals will require their share of medical treatment, fire-fighting and public safety services, and emergency shelter.

In the short term, people already living in high-hazard areas must rely on timely warnings of eruptions provided by HVO and on the ability of Hawaii County Civil Defense to rapidly deliver those warnings and evacuate residential areas. In the long term, the County must grapple with the cost/benefit of purchasing vacant property in high hazard areas versus dealing with the aftermath of a disaster.

Government at all levels tends to be reactive, not proactive. Each disaster, natural or otherwise, galvanizes government and the public to support efforts to reduce the risk of similar future events. Each major disaster spawns a temporary flood of money to reduce future risk. Once the disaster is off the front page, however, public and political support for these programs rapidly dwindles.

Can Hawaii rise to the challenge and set an example for other natural-hazard prone areas around the globe? Time will tell.

### Volcano Activity Update

Eruptive activity at Puu Oo continues. The Banana flow, which breaks out of the Mother's Day lava tube a short distance above Pulama pali, made it to the coastal flat on May 2 and has moved to within one-quarter mile of the coastline. Lava viewing has been good most of the week. The national park has marked a trail to within a short distance of the end of the flow. There is no eruptive activity in Puu Oo's crater except for sporadic minor spattering.

One earthquake was reported felt on the island during the week ending May 20. A magnitude 2.9 earthquake occurred 6 km (3 miles) north-northwest of Keanakolu at 1:25 p.m. May 18 at a depth of 11 km (7 miles). The earthquake was felt at Pa`auilo.

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains low, with only 1 earthquakes located in the summit area during the past week.