THE BIG ONE:
HISTORIC EARTHQUAKES, VOLCANOES, & TSUNAMIS
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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.
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Click on pictures for larger images
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Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, since tectonic processes began on Earth between 3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. © Wikipedia
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| SAN ANDREAS FAULT |
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| NESKOWIN GHOST FOREST (OREGON) |
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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.
The earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake. © Lisa Wald; USGS
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| ALASKA 1964 |
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| CHILE 1960 |
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| SAN FRANSISCO 1906 |
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| EXPLOSIVE VOLCANO |
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A volcano on Earth is a vent or fissure in the planet's crust through which lava, ash, rock and gases erupt. A volcano is also a mountain formed by the accumulation of these eruptive products.
Volcanoes have existed for a long time on Earth, likely causing disasters such as the Permian mass extinction about 250 million years ago, the greatest mass extinction in Earth's history, according to a 2015 paper. Volcanoes can and have existed on other worlds as well: although volcanoes on the moon and Mars have long been dormant, volcanoes are still very active on Jupiter's moon Io. Researchers are currently striving to find ways to predict when volcanic eruptions might happen on Earth by analyzing clues such as crystals and gases linked with volcanoes. © Live Science
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.
Shield Volcanoes are large, broad volcanoes that look like shields from above – hence the name. The lava that pours out of shield volcanoes is thin, so it can travel for great distances down the shallow slopes of the volcano. These volcanos build up slowly over time, with hundreds of eruptions, creating many layers. They’re not likely to explode catastrophically; they are effusive rather than explosaive. Perhaps the best known shield volcanoes are the ones that make up the Hawaiian Islands, especially Mauna Loa and Mauna Kea. © Universe Today
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| VESUVIUS 1944 |
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| MOUNT ST. HELENS 1980 |
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| SIBERIA 250 MILLION BCE |
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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.
Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean. Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane. At that pace, they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way. In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously. © National Geographic
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| INDIAN OCEAN 2004 |
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| JAPAN 2011 |
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| ALEXANDRIA 365 CE |
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WEB RESOURCES:
Ask if your local community—or your apartment/condo building—has an emergency preparedness plan in place. If not, think about starting one. It could save lives—including yours.
EARTHQUAKE PREPAREDNES: https://www.ready.gov/earthquakes
EMERGENCY KITS, BAGS, RADIOS, AND SUPPLIES:
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PACIFIC NORTHWEST "BIG ONE"
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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.
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