One volcano can produce a variety of volcanic hazards when erupting. Some volcanic hazards can happen when there isn’t even an eruption. The more that is known about volcanic hazards, the better prepared communities at risk from these hazards can be.
There are seven types of hazards associated with volcanoes:
- Toxic gas emissions
- Lahars
- Ash columns and flows
- Lava flows
- Earthquakes
- Tsunamis
- Landslides
Tsunamis
Tsunamis are created when volcanic activity produces large earthquakes near coastal areas or massive landslides into the ocean. Because volcanoes do not directly produce tsunamis, this type of hazard is considered a secondary volcanic hazard. Even still, tsunamis that are a result of volcanic activity can be destructive and deadly, approaching populated coastal areas with little or no warning.
Waves of Destruction
Perhaps one of the most infamous tsunamis that resulted from volcanic activity was the tsunami that was created immediately following the August 1883 eruption of Krakatau Volcano in the Soenda Straits. Experts still disagree on what exactly caused the massive tsunamis. It could have been the collapse of the volcano island as millions of cubic meters of magma were ejected from the volcano in the form of pyroclastic flows and ash columns. Or it could have been from all the volcanic material entering the ocean at such a rapid rate.
Whatever the cause of the tsunamis, the thousands of people living in the coastal villages that lined the surrounding Soenda Straits could not have known at the start of the eruption that it would kill them. Krakatau lies in the middle of the Soenda Straits, with coastal cities of Sumatra and Java as many as 100 km (62 miles) away. When the eruption first started – around noon on the August 26, 1883 – people living in these cities could only hear distant rumblings.
As the eruption continued, those closer to the volcano began to see an ash column rising miles above the volcano island. The first deadly hazards were pyroclastic flows and ash falls that made their way across the sea to some of the closer inhabited islands, killing about 4,500 people.
No Warning
Those farther away were not affected by the ash hazards and most were not concerned as they watched the eruption develop from – as they thought – a safe distance. A few hours after the eruption onset, a deadly tsunami was making its way across the Soenda Straits. Those that had survived the pyroclastic flows didn’t even see the tsunamis coming because a thick cloud of ash was still settling down around them.
But the greatest tragedy fell upon those who lived farther away and felt they were at a safe distance from the volcano. Without any kind of warning, the tsunamis from Krakatau killed about 32,000 people inhabiting these far-away coastal villages. In all, over 36,000 people were killed from the volcanic hazards produced by Krakatau, one of the largest volcanic eruptions in recorded history.
Source:
- Scarth, Arwyn. Vulcan’s Fury: Man Against Volcano. London: Yale University Press, 1999.
- Simkin, T., and Fiske, R.S., 1983, Krakatau 1883—the volcanic eruption and its effects: Smithsonian Institution Press, Washington D.C., p. 464
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
