# Volcano Watch — HVO making long-range forecasts

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The Hawaiian Volcano Observatory studies mainly the current activity of Hawaii's volcanoes, and our eruption forecasts are limited to the short-term future (hours, days, months, sometimes a few years).

The Hawaiian Volcano Observatory studies mainly the current activity of Hawaii's volcanoes, and our eruption forecasts are limited to the short-term future (hours, days, months, sometimes a few years). This is the work that enables us to predict when and where Kīlauea or Mauna Loa are likely to erupt next, and to fulfill our basic obligation of protecting lives and property on the Big Island. However, longer-term forecasts of volcanic activity on different parts of our active volcanoes are required by such agencies as planning departments, insurance companies, and mortgage lenders, in order to wisely plan future development or to evaluate the safety of investments.

In order to forecast the long-term future activity of any volcano, one must know what has happened at that volcano in the past. Field studies by U.S. Geological Survey scientists over the past two decades have revealed a great deal about the long-term eruptive history of the Big Island's active (Kīlauea, Mauna Loa, and Hualālai) and dormant (Mauna Kea) volcanoes. These studies provide long-term perspectives of future activity at each of these volcanoes.

How do geologists determine the eruptive history of our volcanoes? Each volcano keeps a record of its past activity—which geologists must decipher—in the lava flows and ash they produce. However, each new lava flowcovers parts of older flows; thus the exposed record becomes increasingly fragmentary as we look further and further into the past. One way to more clearly see some of the older, and now poorly exposed, parts of the volcanoes is to study drill core from wells drilled into the volcano.

Several years ago, the U.S. Geological Survey helped formulate a plan to drill a deep hole through one of Hawaii's volcanoes to develop such a long-term understanding of the volcano. The volcano chosen was Mauna Kea, which - with Mauna Loa - is one of the two largest volcanoes on Earth. It was chosen because it is a young volcano that has nearly completed its active life, unlike Mauna Loa and Kīlauea, which are still growing rapidly. This program, funded by the National Science Foundation, is led by Dr. Don DePaolo from the University of California at Berkeley, Dr. Ed Stolper from the California Institute of Technology, and Dr. Barry Raleigh from the University of Hawaii at Manoa. A 2,000-foot deep pilot hole will be drilled first to test the feasibility of drilling the proposed 14,800-foot hole. The pilot hole will be about the same depth as many water wells drilled on the island. The site was selected to be as far away from the summit and rift zones as possible so that fresh lavas, rather than hydrothermally altered lavas, would be encountered. The location selected for the drill site meets the above requirements and is also favorable for logistical reasons, since it is adjacent to the Hilo harbor facility. The drill hole is expected to encounter about 400 feet of Mauna Loa lava flows before passing into Mauna Kea lava flows. If this program is successful, scientists should have a look at the history of Mauna Kea Volcano for roughly the past half million years.

On a shorter time-frame than will be examined with the drill hole, geologists can determine the history of the volcano by making detailed geologic maps showing individual lava flows. Such maps have recently been published by the U.S. Geological Survey for Hualālai and parts of Kīlauea; mapping is in progress on Mauna Loa. Knowing the distribution of lava flows and ash deposits is only part of the story, however—we also need to determine the ages of the rocks.

There are many methods to determine the ages of lava flows, but Hawaii's active volcanoes are very young (almost all of the lava flows one sees on the surfaces of Hualālai, Kīlauea, and Mauna Loa are less than 10,000 years old), and the only reliable dating method for such young flows is the carbon-14 technique. For this, geologists must recover charcoal from places where plants have been covered and carbonized by advancing lava flows. The collected charcoal is then analyzed to determine the age. These ages indicate when the overlying lava flows were emplaced and, with detailed geologic maps, provide the data to determine how often the volcano has erupted in the past, what the eruptions were like, and where flows traveled most frequently. This record of past activity is our best guide to future behavior.

The new drilling program on Mauna Kea will increase our understanding of its long-term eruptive history and enable us to better forecast future activity. The eruptive history of Mauna Loa will be the subject of a public lecture by Dr. Jack Lockwood on Tuesday evening at 7:00 p.m. at the Hawaii Volcanoes National Park auditorium as part of the "After Dark in the Park" lecture series.

### Volcano Activity Update

As for the nearly 10-year-long eruption on the East Rift Zone of Kīlauea Volcano, it continues from the episode 51 vents on the west flank of the Puu Oo cone. Sluggish pahoehoe flows are moving toward the south. The episode 52 vents on the south flank of Puu Oo, active from October 2 to 14 are now dead. During this past week, strong tremor was recorded near Puu Oo. Such strong tremor usually indicates eruption through a new fissure, but this time was caused by violent circulation of lava inside Puu Oo. On October 20 at 2:45 a.m., a magnitude 3.1 earthquake occurred about three miles southwest of Puu O`o at a depth of roughly 3.5 miles.