Wilkes University’s Sid Halsor, a professor of geology at Wilkes University with expertise in rock-forming processes beneath active volcanoes, offers insights about the eruption of New Zealand’s White Island volcano and why predicting its eruption is challenging.
New Zealand Volcanic Eruption is a Grim Lesson
By Sid Halsor, Ph.D.
The recent eruption of White Island volcano in New Zealand is a tragic reminder of the violently explosive behavior of active volcanoes. Sadly, a group of tourists, presumably enjoying a once in a lifetime experience, were exiting the crater floor as the eruption clock ticked to zero. In an instant, their lives ended, as did several tourists waiting to leave the volcano. Those who survived suffered horrific burn injuries. Many questions remain including why wasn’t this eruption predicted.
Geoscientists, scientists who study the earth, have made considerable progress in predicting volcanic eruptions. The turning point was the 1980 catastrophic eruption of Mount St. Helens in Washington state, the most disastrous eruption in U.S. history. In the months leading to the eruption, U.S. Geological Survey scientists brought state-of-the-art methods that tracked changes in and around the volcano as it grew more restless. When molten rock, or magma, rose up beneath the volcano, it produced natural signals that were monitored by geoscientists. These signals included minor earthquakes, increased release of heat at the volcano’s surface, changes in the proportions of volcanic gases, and slight outward movement of the volcano’s slopes. The geoscientists knew the eruption was imminent when measurements showed rapid expansion of the north slope. Although the ensuing eruption was forewarned, the simultaneous failure of the north slope unleashed an initial, powerful lateral blast that transformed hundreds of square miles of forest into a barren wasteland. An enormous amount was learned about the behavior of erupting volcanoes while geoscientists monitored St. Helens, including that volcanoes do not always erupt initially from their peaks.
Did White Island volcano provide similar signals prior to its eruption? Perhaps, but the style and intensity of unrest at White Island differs from St. Helens with the signals trickier to interpret. St. Helens had not erupted in over 100 years when it exploded. White Island, which above sea level resembles the top of a volcano like St. Helens, erupted several times over the past two decades and these more frequent eruptions were lower in intensity. This means rising unrest leading to a small to moderate eruption may be difficult to distinguish from background level of unrest. Secondly, the White Island eruptions are primarily steam driven and not directly triggered by rising magma. Steam-driven eruptions occur as rain or ponded water seeps down into the volcano where hot rocks cause the water to boil and flash to steam. The resulting explosion spews hot steam mixed with ash upward through a vent or crack in the rock. Since a steam-driven eruption does not deform the volcano’s surface like denser magma beneath St. Helens, measurements of uplift in and around White Island are often ambiguous. Lastly, 70 percent of White Island volcano is below sea level leaving a relatively small portion that is readily accessible to scientists. Though the emergent crater is the focus of both volcanic and monitoring activity, the whole of the volcano is not monitored and this inhibits the integration of a network of methods used to predict eruptions.
It is ironic that the sea that prevents comprehensive monitoring of White Island provides convenient access to the crater. A 90-minute boat ride can land a tourist at the open crater floor. To get that perspective at other volcanoes usually means a long, rigorous hike or climb. To get within a mile of St. Helens’ crater requires a 15-mile hike and about 25,00 feet of elevation gain (entry into the crater is prohibited). So it’s easy to understand why a White Island tourist would want to experience the full awe of a volcano while standing at ground zero, the smoking gun of past eruptions. Tourists assume that they can do this safely and that all the necessary precautions are taken between the tour provider, the owner of the island and the New Zealand agency of geoscientists monitoring the volcano. Countless tours have played out safely, but not on Dec. 9, 2019. On this day, White Island volcano grimly showed the triad of overseers that predicting its eruption remains a work in progress.