Lecture: Predictions of Volcanic Activity: Narrator: Listen to part of a lecture in the geology class. Professor: Last time when we talked about the different types of volcanoes, active, dormant and extinct, someone asked whether we can predict when an active volcano will erupt. The answer's a qualified yes. We can sometimes make short-term predictions of volcanic activity. We can't really pinpoint exact date, but we can say with relative confidence that a given volcano will erupt sometime in the next few months, weeks, or days. But before talking about short-term predictions, let me talk a minute about long-term predictions. Um, even the earth's most active volcanoes don't erupt continuously, right? They erupt intermittently, periodically. We call this pattern of eruptions the recurrence interval. The recurrence interval is the period of time between successive eruptions and this period can range from a few years to a few centuries, and in some cases a few millennia depending on the volcano. As far short-term predictions, um, you recall that short-term predictions aren't feasible for earthquakes. Earthquakes tend to strike without warning but volcanoes at least some of them send out distinct warning signals announcing that an eruption could occur in the very near future. Um, the warning signs begin when molten rock, magma, migrates upward through cracks and collects in a magma chamber. Quick review someone magma chamber? Student: It's like an underground pool of magma, a few kilometers below the surface where the lava comes from during a volcanic eruption. Professor: Good, Now, as more and more molten rocks squeeze into the magma chamber, a number of changes occur. These are warning signs that we can measure, at least four signs. First, there is an increase in heat flow. Heat from the magma radiates up through the bedrock, and eventually to the volcano surface. We can measure that heat and in some cases the increased heat flow melt snow or ice on the volcano triggering floods. Another clue is the volcano's shape. The increasing pressure in the magma chamber is pushing the magma outward to the point of creating a ball on the surface of the volcano, kind of like blowing up a balloon. A classic example of this is Mount Saint Helens in Washington State. About two months before Mount Saint Helens erupted in 1980, the north side of the volcano began bulging outward up to one and a half meters a day. This was caused by pressure from the magma that was building up below. Ultimately the size of the bulge grew to over 100 meters which in a period of only two months is an enormous change and this is not uncommon. Okay, so the third sign of impending eruption is that when the magma chamber fills, rocks surrounding the chamber crack and blocks slipped past one another, Such cracking and shifting causes what? Student: Earthquakes? Professor: Right. The movements in the rock trigger small to medium-sized earthquakes in the immediate area of the volcano and gas bubble's forming an exploding within the magma. These bursting bubbles also register earthquakes. So when we detect seismic activity, small to medium sized earthquake activity, deep below the volcano and the frequency of these earthquakes increases, we can be fairly sure that an eruption will occur within a few days or weeks. The last thing that often happens before an eruption is we can see gas and steam escaping to the volcano's vent. The gas counts those bursting bubbles in the magma. Gases percolate up through cracks in the earth and eventually find their way to the volcano's vent. The steam comes from groundwater heating up due to heat flow from the rising magma. When this happens, an eruption is usually imminent. An example of this is Mount Pinatubo in the Philippines. In 1991 we detected increasing levels of sulfur dioxide being released from Pinatubo's vent. Within two weeks the sulfur dioxide emissions had increased tenfold to 5,000 tons. And about two weeks after that Mount Pinatubo erupted. Student: I think our textbook says something about hot springs, that monitoring hot springs can help predict an eruption. Professor: Oh, yes, not to be overlooked. Monitoring hot springs. Um, when a new hot spring develops or when the temperature of an existing hot spring rises. These are other indications that magma has entered the magma chamber and is heating things up.