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Time-lapse multi-image movie of Pu‘u ‘O‘o Crater
(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
It is natural for most people, including scientists, to think that the aim of a volcano observatory is to observe and measure ongoing activity, catalog the observations and monitoring data, and try to anticipate what might happen next on the basis of that information. Such tasks are indeed what most of HVO’s scientists do most of the time. The societal benefits of using today’s observations to forecast tomorrow’s events are obvious. Moreover, repeated measurements of similar events provide tests of models developed to explain the observations.
But what about next year’s volcanic activity, or next decade’s, or next century’s? On these longer-term time scales, today’s observations become less useful. To anticipate what might happen a long time in the future, we must look at a longer record of past events to get a better understanding of what the volcano is capable of doing. What is happening at present is only a small sampling of what has happened in the past. The “present” is a few days to a few years, but the past is so much longer (more than 200,000 years for Kilauea) that many different kinds of volcanic activity have been able to take place. Indeed, as one wag puts it, we must use the heretofore rather than the here and now to best judge the hereafter.
That is why a small portion of HVO’s effort is designed to understand the past centuries of volcanic activity at Hawai`i’s active volcanoes. This approach is not very expensive and is even under the radar much of the time. At meetings of earth scientists, such as the 22,400 who attended last week’s American Geophysical Union meeting in San Francisco, most of the volcanology sessions focus on current measurements and generally minimize the broader-scale problems on a centuries and millennia time scale. Nonetheless, volcanologists acknowledge the need to understand the past in order to anticipate the full range of events that might occur in the future.
Two examples of recently recognized past activity at Kilauea provide guides for the future. The first is that explosive activity has been common in the past and therefore will almost certainly be common in the future. Our current understanding of Kilauea’s past explosive eruptions leads to the realization that impacts won’t be confined to only the summit of the volcano—though that is where most of the danger will be. The larger eruptions will send ash to heights where air traffic would be negatively affected. With the island—and indeed the state—heavily dependent on air transportation, the possibility of disruptions caused by repeated explosive activity takes on considerable importance.
The other example is the realization, reached only in the past 18 months, that periods of dominantly explosive activity have lasted for long times in the past—300 years for the most recent periods, and 1,200 years for the period before that. Should such long periods recur—and there is no reason to think that they won’t—imagine the potential impacts on local society. Island residents put up with 300 years of explosive activity between 1500 and 1800, but our infrastructure is far more diverse now, and, during the next explosive century, society will face more challenges than did precontact people.
Current day-by-day monitoring provides no clues regarding these long-term issues. That is why it is always important to integrate the geologic studies with the monitoring in order to provide the broadest range of possibilities regarding future decades. Among volcano observatories, HVO is one of the world’s leaders in recognizing the importance of the past as a guide to the future and in integrating the vastly different time scales of the present and the past in order to provide a well-grounded anticipation of the future.
It is always necessary to conclude an article such as this by reassuring readers that we foresee no important changes in volcanic activity in the near future. We do, however, want to remind readers that, at some currently unknown time in the future (years, decades, centuries?), major changes will occur at Kilauea. The past doesn’t lie. It is discounted, ostrichlike, only with peril.
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Time-lapse movie of Pu‘u ‘O‘o Crater’s East flank