Pillow Lava
Pillow lava is lava that comes out from volcanic vents underwater (Figure 8.18). When
it comes out underwater, it cools down very quickly and forms roughly spherical rocks
that resemble pillows, from which more lava leaks and creates more pillows. Pillow lava is
particularly common along underwater spreading centers.
Figure 8.18: Pillow lava. ( 3 )Predicting Volcanic Eruptions
Volcanic eruptions can be devastating, particularly to the people who are closer to volcanoes.
As meteorologists attempt to predict, or forecast, hurricanes and tornados, so too do volca-
nologists attempt to forecast volcanic eruptions. Although predicting volcanic eruptions is
far from perfect, many pieces of evidence can indicate that a volcano is about to erupt. Some
of those factors are hard to measure, contributing to the difficulty in predicting eruptions.
History of Volcanic Activities
One important factor in predicting eruptions is a volcano’s history. That is, we consider how
long since it has erupted and the time span between its previous eruptions. Volcanoes are
categorized into three subdivisions—active, dormant, and extinct. Anactivevolcano is one
that is currently erupting or shows signs of erupting in the near future. Adormantvolcano
no longer shows signs of activity, but has erupted in recent history (Figure8.19). Finally,
anextinctvolcano is one that has not erupted in recent history and will probably not erupt
again in the future. Both active and dormant volcanoes are heavily monitored because even
dormant volcanoes could suddenly show signs of activity.