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Volcanowatch

June 10, 2010

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Dealing with Hazards is a Risky Business

Volcanic hazards come in many forms. The most common hazards for Hawai'i include earthquakes, lava flows, and wide-ranging vog. What is the definition of hazard?

Merriam-Webster defines "hazard" as a source of danger. Other definitions from dictionary.com include 1) an unavoidable danger or risk, 2) something causing unavoidable danger, peril, risk, or difficulty. In the last two definitions, the term "risk" is introduced. What is "risk"?

"Risk" is defined by dictionary.com as "exposure to the chance of injury or loss; a hazard or dangerous chance." In volcanology, risk has been defined as the impact (damage) that an event would have on humans within the area affected. This extends to person(s), property, or anything of economic value.

Risk can be defined as the mathematical product of hazard, vulnerability, value, and likelihood (assuming that these concepts can be expressed in numbers).

Everyone on the Island of Hawai`i should be aware of the fact that there are at least three active volcanoes and that lava flows present a significant hazard. The most persistent hazard is vog. Yet, the most damaging hazard is a large earthquake, such as the 2006 Kiholo Bay earthquake that impacted communities as far away as O`ahu.

Simply defined, "vulnerability" is the percentage of value likely to be lost if a hazardous event occurred. If lava contacts your wooden house, it will burn; the house is 100 percent vulnerable. Many houses survived the 2006 Kiholo Bay earthquake with minor damage thanks to improved building codes; therefore, the vulnerability was a small fraction of the cost of a new home.

"Value" is defined explicitly as the dollar amount of life and (or) property that is lost by a hazardous event. Some things are easily tabulated because we see and use them in everyday life—homes lost, roads buried, electrical poles burnt, TV and Internet cables damaged, etc.—and are components of fixed infrastructure; they are relatively easy to quantify.

We would be remiss in future risk assessment if we ignored the loss of productive capacity or the economic loss due to a hazardous event, where businesses and people are unable to earn money.

For example, what would happen if a flow from Mauna Loa advanced down the flank of the volcano and entered the ocean? It is plausible that no homes would be impacted by such a flow, yet highways would be severed, commerce would be impeded, workers could not get to their jobs because travel would be disrupted. The loss of future earnings is harder to assess and has wide-ranging repercussions.

"Likelihood" is often incorporated into the term "hazard" in the risk equation. It is often expressed in terms of probability. Probability estimation is not an easy task and, for lava flow hazards, is based on lava flow ages. To do the best job, we need to determine the recurrence interval (RI) for all lava flows, and this requires access to all lands impacted by lava.

The RI is the average time between past lava flows. For example, in the 167 years since 1843, Mauna Loa has erupted 33 times; 167 years divided by 33 eruptions is about 5 years between lava flows.

Probability and recurrence interval vary inversely. The shorter the RI, the larger the probability that a lava flow will occur in a given period. In our example, the probability of a Mauna Loa eruption occurring in any one year is about 1/5 or 20 percent. Probability can be a difficult concept for many people to grasp. Geologic hazards are generally considered to be random events; there is an equal chance that it will occur in any given year. Passage of a significant amount of time since the last hazardous event does not necessarily mean that there is a greater chance of another one occurring.

Geologic hazards are a reality of living on the flanks of active volcanoes. It is important to know what those hazards are. Risks can be reduced by being prepared and planning for hazardous events. Furthermore, land use planning is the most effective tool for mitigating lava flow hazards. All in all, living on the flanks of volcanoes can be a risky business.

Kīlauea Activity Update

Over the past week, activity on the east rift zone flow field remains focused on the construction of low shields. This activity was located well above the Pulama pali, over the breakout point of the Quarry flow. Weak activity continues along the Quarry flow itself from the top of the pali to the coastal plain. In addition to that lava erupting and flowing through the TEB and Quarry flow tube systems, lava is also erupting from two vents within Pu`u `Ō `ō. These vents are slowly filling Pu`u `Ō `ō's crater, and the Webcam on Pu`u `Ō `ō has been providing spectacular views both day and night.

At Kīlauea's summit, a circulating lava pond deep in the collapse pit within the floor of Halema`uma`u Crater was visible via the Webcam throughout the past week. The baseline lava level continues to rise slowly and was punctuated a few times by short-lived lava-level increases that brought the lava surface to its highest level yet recorded. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

No earthquakes beneath Hawai`i Island were reported felt during the past week.

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.

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Updated: July 25, 2010 (pnf)