THE BIG ONE: HISTORIC EARTHQUAKES, VOLCANOES, & TSUNAMIS
For those of us living in the Pacific Northwest, nearly every day brings us public service announcements on our local television stations regarding earthquake preparedness--and a drive down any stretch of the 101 reveals signs every few miles showing tsunami evacuation routes. In other words, we’re reminded regularly that we Washingtonians and Oregonians live in an active earthquake and volcano zone. This page allows you to explore some of the major seismic and volcanic events of the last few thousand years--not only in our region, but around the world--and helps separate fear-filled hype from science-based facts. Here you can examine the causes for earthquakes and volcanoes, how tectonic movement changes our planet across time, and explore cutting edge technology that’s being used to predict when and where the next event might occur. Also listed here are resources to help you prepare in the event of a geological or oceanic emergency.
An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock.
Composite cone volcanoes, which are also called 'stratovolcanoes' or simply 'composite volcanoes,' are cone-shaped volcanoes composed of layers of lava, ash and rock debris. Composite cone volcanoes are grand sites and can grow to heights of 8,000 feet or more. Mount St. Helens and Mount Rainier, which are both found in Washington State, are impressive examples of composite volcanoes. These steep-sided volcanoes erupt in an explosive manner.
A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore. These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly, it displaces the water above it and launches the rolling waves that will become a tsunami. Most tsunamis–about 80 percent–happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
As of today, there's no completely accurate way to predict exactly when an earthquake (and its possible tsunami) or volcano will occur. But there’s a lot of cutting edge science taking place that makes it possible to make “educated” assumptions and guesses. More than ever, speaking in terms of “probabilities” is far more a reality than it was a decade ago. As time goes on, and more pioneering discoveries are made, accurate prediction may become more than a mere possibility. Here are some resources that examine what’s currently happening in volcanology, seismology, and oceanography.