Seafloor topography map source: Global sea floor topography from satellite and ship depth soundings, 1997, by W. H. F. Smith and D. T. Sandwell, Science, v. 277, p. 1956-1962. When two plates are moving away from each other, we call this a divergent plate boundary. 1). The San Andreas Fault that runs through much of California is an enormous transform plate boundary. Tsunami waves can hit with the devastating force of a powerful tornado. The granite rocks in the foreground are similar to those found in Yosemite National Park in the Sierra Nevada Mountains. The collision of tectonic plates can result in earthquakes, volcanoes, the formation of mountains, and other geological events. And as the Pacific Plate dives, it slopes downward. Volcanic eruptions and shallow earthquakes are common where plates rip apart. View from the playground of the Government Hill School in Anchorage, showing damage from the 1964 earthquake. Which type of boundaries can produce earthquakes? Sometimes the valleys are partially filled with water, as at Point Reyes National Seashore, where Tomales Bay and Olema Valley follow the main trace of the San Andreas Fault. This is called subduction. Sign up for the Academys monthly newsletter and get a promo code for 10% off at our online retail store. Scientists also confirmed that earthquake-related tsunamis arent always localized and can happen thousands of miles from the epicenter. For more earthquake and tsunami data, images, and educational materials, visit NCEIs Natural Hazards website . This is an earthquake. Alaskan tectonics are dominated by the Pacific-North American plates. The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands.The trench extends for 3,400 kilometres (2,100 mi) from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril-Kamchatka Trench, to a junction with the northern end of the Queen Charlotte . She now estimates that it takes at least 500 years of plate motion to set the stage for such big earthquakes. When this happens, some part of the surface is said to subside. Its like opening a sticky window or door. Parks in the Sierra Nevada, including Yosemite, Kings Canyon, and Sequoia national parks, contain granite-type rocks that cooled within magma chambers beneath ancient subduction zone volcanoes. convergent boundaries The edges of two neighboring tectonic plates that are colliding into one another. Was the 1964 Alaska earthquake was the first time earthquakes were linked to plate tectonics? NS = National Seashore That raised rock runs from the right foreground to the left background. in that one quake, it was the first time that you could actually see plate motion in action. Layers of ocean sediment were squeezed and contorted as they were caught in the vise of the converging plates at the ancient subduction zone. The pinnacles are the eroded remnants of hardened volcanic brecciaslurries of mud and rock from explosive eruptions. Farther east, the continent began to rift apart in the Basin and Range Province. Short video (4 min) by Stephen Wessells, USGS relating how the largest quake in U.S. history had profound and lasting impacts on our lives. You push and push. This led to the establishment of the Pacific Tsunami Warning Center (originally called the West Coast/Alaska Tsunami Warning Center) to alert people when a widespread tsunami is possible. An animation that describes earthquakes along the Aleutian subduction zone, one of the most seismically active in the world, and the Queen Charlotte Transform Fault. That doesnt seem like much, but over time it adds up. The San Andreas Fault Zone is not the only active transform plate boundary with U. S. National Park Service sites. Warping resulted in permanent tilt of larger lake basins and temporary reductions in discharge of some major rivers. By midnight, 131 people were dead. The 1964 Alaska Earthquake taught coastal citizens to run for higher ground at the first sign of strong tremors. Aug. 16, 2013. The land that was uplifted and sometimes dropped by the Great Alaskan Quake also fits with the plate-tectonics model. subduction zone A large fault where one tectonic plate sinks beneath another as they collide. The San Andreas Transform Plate Boundary developed within the past 40 million years as a large portion of the Farallon Plate was subducted and the Pacific Plate made contact with the North American Plate in the California region. National Park Service sites in the Transverse Ranges include Santa Monica Mountains National Recreation Area and part of Joshua Tree National Park. Where do earthquakes happen besides plate boundaries? U.S. Geological Survey For example, rocks found today in Point Reyes National Seashore north of San Francisco were originally part of the line of granite rocks formed beneath ancient subduction zone volcanoes. A plate boundary is a three-dimensional surface or zone across which there is a significant change in the velocity (speed or direction) of motion of one lithospheric plate relative to the adjacent lithospheric plate. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. Beginning about 30 million years ago, so much of the Farallon Plate was consumed by subduction that the Pacific and North American plates were in contact, forming the San Andreas transform plate boundary in western California. National Park Service Sites (shown in red) Regional vertical deformation generated a train of destructive long-period seismic sea waves in the Gulf of Alaska as well as unique atmospheric and ionospheric disturbances that were recorded at points far distant from Alaska. Compaction in the Rock Cycle: Understanding the Process Behind Sedimentary Rock Formation, Crystallization in the Water Cycle: A Fundamental Process in Water Distribution and Purification, Understanding Crystallization in the Rock Cycle: A Fundamental Process in Rock Formation, Extracting Lat/Lng from Shapefile using OGR2OGR/GDAL. Faults are fractures in Earths crust where movement has occurred. This resulted in a line of volcanoes stretching all the way from what is now Alaska to Central America. The 1964 Alaska Earthquake and Tsunami lecture by George Plafker, USGS Geologist Emeritus. Channel Islands National Park includes five islands that are the tops of a mostly-submerged portion of the Transverse Ranges. All rights reserved. In particular, We were looking for evidence of surface faulting, he recalled at a press briefing earlier this week. July 6, 2011. Along much of the boundary, the bulk of the motion occurs along the San Andreas Fault. UA is committed to providing accessible websites. The convergent boundary happens when two plates slide toward each other to form a subduction zone or a continental collision. Along convergent boundaries, neighboring plates either collide head-on or a denser ocean plate dives beneath a lighter continental plate. The San Andreas Fault is just one of many active earthquake faults in a broad zone of shearing along the transform plate boundary in the San Francisco Bay Area. The map shows the epicenter of the 1964 Alaska Earthquake (red star), caused when the Pacific Plate lurched northward underneath the North American Plate. Plate boundaries are found at the edge of the lithospheric plates and are of three types, convergent, divergent and conservative. Monday Saturday: 9:30 am 5 pm Plate boundaries from The Plates Project, University of Texas Institute for Geophysics. The movements of the plates help shape the geological features of our planet. When the fault finally slips, its like a rug flattening out. This subduction zone landscape was later plucked from the edge of the North American Plate and transported nearly 200 miles northwestward along the San Andreas Fault. uplift A upward shift in some section of Earths surface due to tectonic activity along a fault. Maximum indicated uplift in the Alaska and Aleutian Ranges to the north of the zone of subsidence was l feet. URL: https://pubs.usgs.gov/pp/0543i/ http://earthquake.usgs.gov/. ), rupture processes, elastic rebound, and resulting tsunami. When the earthquake hit, the ground underlying the road shimmied, fissured and then split apart. These plates constantly move. At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaskas earthquakes, including the 1964 earthquake. Earthquakes and tsunamis can happen along any coastline, at any time of the year, but Alaska is particularly prone to them because it sits on the convergence of two tectonic platesthe Pacific Plate and the North American Plate. USGS.The 1964 Tsunami Strikes Valdez. The 1964 earthquake was a defining moment in a territory that had just achieved statehood. And they are powerful. The tsunamis created by the earthquake reached land within a few minutes of the ground shaking and engulfed some areas as much as 170 feet above sea level. The Earthquake Trail at Point Reyes weaves back and forth across the fault line. March 21, 2011. Explains how Yakutat terrane accretion drives mountain building and crustal fault earthquakes like the 2002 M7.9 Denali Earthquake. Valdez was basically leveled. A transform plate boundary developed where the Pacific Plate was in contact with the North American Plate and the volcanism ceased in central California. The plate boundary is a broad zone of deformation with a width of about 60 miles (100 kilometers). Exhibits along the trail include the reconstruction of a fence that was offset 16 feet (5 meters) during the 1906 earthquake. Modified from Earth: Portrait of a Planet, by S. Marshak, 2001, W. W. Norton & Comp., New York. March 27, 1964, was a quiet day in Alaska. When oceanic and continental plates meet, the denser oceanic plate moves under the less dense continental plate. plate boundary (in geology) The edge of a tectonic plate, or the place where two or more tectonic plates meet. Plate boundaries. On March 27, 1964 at 5:36pm local time (March 28 at 3:36 UTC) an earthquake of magnitude 9.2 occurred in the Prince William Sound region of Alaska. The publication, as well as Science News magazine, are published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education. This pattern has since been seen at other subduction zones. The demolished towns of Valdez and Chenega were rebuilt on higher ground, but not everyone was prudent about rebuilding on earthquake-prone land. East to west, nearly 960 kilometers (600 miles) of fault had ruptured at once. Thats a type of convergent plate boundary where one plate dives beneath another. Scientists learned that at the point where the North American Plate overrode the Pacific Plate, it descended into a subduction zone. Eyewitnesses described hearing a crunching, grinding noise as the earth shook. This opinion piece by USGS geologist Peter Haeussler, et al. For more information on how you can prepare for a tsunami, visit the National Tsunami Hazard Mitigation Program. Heres evidence of the impacts of those waves that surged into the deep-water port of Whittier after the earthquake. Yet as dusk approached on this Good Friday, just two days before Easter, a major upheaval was in store. As Europe and Africa move away from North and South America at about 1 inches (4 centimeters) per year, the Atlantic Ocean has opened to a width of 4,000 miles (6,000 kilometers) in the past 150 million years! Contact Information, Menlo Park, Calif. Together, these destructive waves swept Alaskas coastline with devastating speed and power. HISTORY reviews and updates its content regularly to ensure it is complete and accurate. Porosity increases, probably related to horizontal displacements in the zone of subsidence, were reflected in lowered well-water levels and in losses of surface water. Out of great catastrophe arises innovation and a new hope for the future of disaster preparedness. On This Day: Great Alaska Earthquake and Tsunami, Aftershocks from the quake continued for three weeks, Transoceanic tsunami waves swept across the Pacific and reached as far away as Hawaii and Japan, The earthquake and ensuing tsunamis caused about $311 million in damages in 1964(about$2.3 billiontoday), Tsunami Warning Centers issue tsunami warnings in minutes, not hours, after a major earthquake occurs, National Tsunami Hazard Mitigation Program, Tsunami Forecast Model Animation: 1964 Alaska Earthquake, NCEI Great Alaska Earthquake Image Database, VIDEO: NCEI Ask a Scientist with Nic Arcos: Tsunamis. A documentary chronicling the first 72 hours after the 1964 Alaska Earthquake and the response to the disaster by the United States Office of Civil Defense, U.S. Military, and local, state, and federal officials. Then suddenly, it pops open. Ideas for using videos, articles, and infographics about earthquakes in the classroom. In that one quake, it was the first time you could actually see plate motion in action. The transform plate boundary between the Pacific and North American Plates in western California formed fairly recently. Most of Alaskas mainland felt the magnitude 9.2 earthquake, which wobbled Seattles Space Needle some 1,200 miles away. Plafker spent most of the summer in Alaska researching and documenting the earthquake. In the Caribbean Sea, the U. S. Virgin Islands lie along a transform plate boundary where the small Caribbean Plate moves eastward past the oceanic part of the North American Plate. The primary fault, or zone of faults, along which the earthquake occurred is not exposed at the surface on land. Some of the plates have ocean water above them. As the plates move past each other, they sometimes get caught and pressure builds up. Every century or so a large earthquake is necessary to release stress accumulated along large segments of the San Andreas Fault that lock rather than slip smoothly. These quakes at transform faults are shallow focus. Southeast of Florida, the Caribbean Plate is sliding east-northeast about 0.8 inches (2 centimeters) per year relative to the North American Plate. What kind of plate boundary causes mountains to form? And it moved parts of the Alaskan coast 15 meters (50 feet) toward the sea. Still, the fact that it reached those areas at all is testament to the enormity of the quake. Photo courtesy of Robert J. Lillie. But this was no ordinary tremor. NRA = National Recreation Area Privacy As the plates move past each other, they sometimes get caught and pressure builds up. Photos and illustrations above modified from Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965. Do earthquakes occur at divergent plate boundaries? subsidence A downward shift in some section of Earths surface. Other plates include continents, and some plates include both continents and ocean. The lithosphere is relatively rigid and is broken into slowly moving tectonic plates. As the mid-ocean ridge separating the Farallon and Pacific Plates entered the subduction zone, the Farallon Plate separated into the Juan de Fuca and Cocos Plates. Do Transform boundaries cause earthquakes? As convergent plates collide, the overriding or top plate gets slowly pushed up. Plates beneath the oceans are much thinner than those under continents. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . The fissure shown here is about 1.5 inches wide. This 3-panel image shows a simplified representation of a tsunami-generating earthquake cycle on the Alaska-Aleutian Megathrust. to A.D. 2022, U.S. Drought: Weekly Report for April 25, 2023, U.S. Drought: Weekly Report for April 18, 2023, U.S. Drought: Weekly Report for April 11, 2023. When the earthquake struck, seismic waves caused soil liquefaction and a portion of the delta slumped into Port Valdez, taking much of the ports resources, living and otherwise, with it. The average movement of the Pacific Plate past the North American Plate in California is about 2 inches (5 centimeters) per year. But if you see something that doesn't look right, click here to contact us! W.R. Hansen/USGS, 1964 Alaska quake files. The earthquake triggered a swell of devastating tsunamis, landslides and submarine slumps which caused massive property damage and loss of life. The types are ocean-ocean, ocean-continent, and continent-continent. Off the coast of Alaska lies the Aleutian subduction zone-a 2,500 mile long convergent plate boundary where the Pacific Plate subducts under the North American Plate at a rate of 6-7 cm/yr. The boundary type that produces the most earthquakes is convergent boundaries where two continental plates collide earthquakes are deep and also very powerful. tectonic plates The gigantic slabs some spanning thousands of kilometers (or miles) across that make up Earths outer layer. Download the latest version of Adobe Reader, free of charge. The water drove a long, 2-by-6-inch-wide plank through a trucks 10-ply tire. It caused extensive damage to the city, including fires that lasted for several days, and killed an estimated 3,000 people. Point Reyes National Seashore and Golden Gate National Recreation Area are the only two NPS sites that are right on the San Andreas Fault. Seismicity of the United States, 1568-1989 (Revised), S. Ornes. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute. It turned out that the ramps shape was very, very significant. A convergent plate boundary is a location where two tectonic plates are moving toward each other, often causing one plate to slide below the other (in a process known as subduction). Systematic horizontal movements of the land relative to bodies of confined or semiconfined water may have caused unexplained short-period wavessome of which were highly destructiveobserved during or immediately after the earthquake at certain coastal localities and in Kenai Lake. They occur where plates are subducting, spreading, slipping, or colliding. IRIS video directed by Robert F. Butler explaining the science behind the earthquake. Credit: Photo Courtesy of Robert J. Lillie. This was the Big One. The Cascades are the modern volcanic arc developing where the Juan de Fuca Plate subducts beneath the North American Plate. For western California, each slipping card face would be a fault surface. See whats revealedevery Thursday at NightLife. The earthquake was accompanied by vertical displacement over an area of about 520,000 square kilometers. Now, 50 years later, plate tectonics is no longer a clever hypothesis. Part of the of the Million Dollar Bridge at Copper River also crumpled. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. Like many of the rocks that are caught up in the zone of transform motion between the Pacific and North American plates, the rocks at Channel Islands National Park were deformed as part of the accretionary wedge during earlier subduction of the Farallon Plate. The dynamics of a subduction zone explained why the 1964 earthquake was so massive. It effortlessly toppled telephone poles, buckled railroad tracks, split roads in half, uprooted buildings, cars and docks and tore homes apart. Over 80 per cent of large earthquakes occur around the edges of the Pacific Ocean, an area known as the Ring of Fire; this where the Pacific plate is being subducted beneath the surrounding plates. by Carl W. Stover and Jerry L. Coffman, As the tremors ended, local tsunamis sprung up almost immediately, leaving residents little to no time to flee for higher ground. Feature labels. Earthquakes occur along fault lines, cracks in Earths crust where tectonic plates meet. Federal government websites often end in .gov or .mil. April 27, 2012. Transform boundaries are places where plates slide sideways past each other. The Alaska earthquake was a subduction zone (megathrust) earthquake, caused by an oceanic plate sinking under a continental plate. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . This megathrust fault has been the source of many large earthquakes including the 1964 Alaskan earthquake that registered a magnitude 9.2 and remains the second largest earthquake in . They also sought to locate the quakes epicenter. Right image The Great Rift Valley in Africa, the Red Sea and the Gulf of Aden all formed as a result of divergent plate motion. This report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. The epicenter of the 1964 quake occurred deep beneath the Chugach Mountains, shown here some time later. Remnants of the ancient volcanic mountain chain remain. The earthquake lasted approximately 4.5 minutes and is the most powerful recorded earthquake in U.S. history. In Valdez, the ground beneath the harbor slumped and nearly swallowed a ship docked there. (For example, the 2011 magnitude-9.0 earthquake off the eastern coast of Japan that unleashed a huge tsunami also was a megathrust earthquake.) The accretionary wedge rocks are found in Channel Islands National Park, Golden Gate and Santa Monica Mountains national recreation areas and Cabrillo National Monument.
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