It effortlessly toppled telephone poles, buckled railroad tracks, split roads in half, uprooted buildings, cars and docks and tore homes apart. 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. We interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great Alaska earthquake. This sudden displacement of the ocean floor, along with earthquake-induced landslides, generated massive local tsunamis that resulted in 70 percent of the fatalities in southern Alaska. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. The earthquake and ensuing tsunamis caused about $311 million in damages in 1964(about$2.3 billiontoday). The route is dotted by some serious volcanoes and wracked by violent earthquakes. It is also the second largest earthquake ever recorded, next to the M9.5 earthquake in Chile in 1960. Now, 50 years later, plate tectonics is no longer a clever hypothesis. Naturally, most of the action occurs along the edges of tectonic plate. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, began under Prince William Sound. The pinnacles are the eroded remnants of hardened volcanic brecciaslurries of mud and rock from explosive eruptions. Identifying port numbers for ArcGIS Online Basemap? Other plates include continents, and some plates include both continents and ocean. Alaskan tectonics are dominated by the Pacific-North American plates. the earthquake and tsunami caused the deaths of over . USGS published the results of investigations of the Alaska earthquake of March 27, 1964 in a series of six Professional Papers. Chile earthquake of 1960, the largest earthquake recorded in the 20th century. Deformation along the transform plate boundary in California can be visualized by placing a deck of cards between your hands in a praying position. Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute. In Alaska, more than 50 volcanoes have erupted over the last 250 years. The San Andreas Fault is the transform plate boundary where a thin sliver of western California, as part of the Pacific Plate, slides north-northwestward past the rest of North America. The 1964 Alaska Earthquake and Tsunami lecture by George Plafker, USGS Geologist Emeritus. There are three main types of plate boundaries: Convergent boundaries: where two plates are colliding. Find History on Facebook (Opens in a new window), Find History on Twitter (Opens in a new window), Find History on YouTube (Opens in a new window), Find History on Instagram (Opens in a new window), Find History on TikTok (Opens in a new window), Education Images/Universal Images Group/Getty Images, Department of Homeland Security & Emergency Management, https://www.history.com/topics/natural-disasters-and-environment/1964-alaska-earthquake. Reports of residual water sloshing (seiches) came in from the U.S. Gulf Coast and as far away as Australia. Other rocks in the San Francisco Bay Area were originally part of an accretionary wedge, similar to rocks found today in the coastal ranges of the Cascadia Subduction Zone in northern California, Oregon, and Washington. Geologic data indicate that the earthquake-related tectonic movements were but the most recent pulse in an episode of deformation that probably began in late Pleistocene time and has continued intermittently to the present. As the plates collide, the oceanic plate is forced beneath the continental plate. The map shows the epicenter of the 1964 Alaska Earthquake (red star), caused when the Pacific Plate lurched northward underneath the North American Plate. An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates.Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. Convergent boundaries , where two plates are moving toward each other, are of three types, depending on the type of crust present on either side of the boundary oceanic or continental . Farther to the south, the Pacific Plate slides past the North American Plate. This causes the crust to crack and form faults where earthquakes occur. plate tectonicsThe study of massive moving pieces that make up Earths outer layer, which is called the lithosphere, and the processes that cause those rock masses to rise from inside Earth, travel along its surface and sink back down. NRA = National Recreation Area Like a jigsaw puzzle, Earths lithosphere is divided into interlocking pieces, called plates. Tomales Bay is the surface expression of the San Andreas Fault, seen in the photo below. This feature includes the famous San Andreas Fault, responsible not only for destructive earthquakes, but also for the spectacular scenery of the San Francisco Bay area and other coastal regions of California. The site is secure. It was the largest U.S. earthquake ever recorded, and a turning point in earth science. Sometimes a sub-surface cave becomes too weak to support the ground above it. Special Earthquakes, Earthquake Sequences, and Fault Zones. The 1964 earthquake in Anchorage, Alaska occurred as a result of an oceanic plate sinking under a continental or land plate. Scientists learned that at the point where the North American Plate overrode the Pacific Plate, it descended into a subduction zone. It includes the crust and uppermost mantle.) The grinding action between the plates at a transform plate boundary results in shallow earthquakes, large lateral displacement of rock, and a broad zone of crustal deformation. FOIA Plates beneath the oceans are much thinner than those under continents. The San Andreas Fault is responsible for most of the movement in western California, causing a sliver of the state to slide past the rest of the continent. The earthquake lasted approximately 4.5 minutes and is the most powerful recorded earthquake in U.S. history. Download the official NPS app before your next visit, Plate Tectonics and Our National ParksSite Index, Plate TectonicsThe Unifying Theory of Geology, Tectonic Settings of NPS SitesMaster List. Success! This stretch of road had been built partly atop mud from a tidal estuary and other unsecure soils. Transform boundaries where plates slide passed each other. Magnitude type: M l 2; Event type: earthquake; Tectonic Setting of Southern Alaska . (The lithosphere is Earths outer solid layer. Comparable horizontal movements are presumed to have affected those parts of the major zones of uplift and subsidence for which retriangulation data are unavailable. . Local tsunamis also caused destruction in Kodiak, Whittier and Seward. Afterwards, geologists realized subduction zonesareas where two tectonic plates (huge slabs of rock made of the earths crust and upper mantle) meet and one bends under the otherplayed a major role in creating the immense Alaskan quake. At an ocean-ocean convergent boundary, one of the plates (oceanic crust and lithospheric mantle) is pushed, or subducted, under the other (Figure 4.6. Scientists also confirmed that earthquake-related tsunamis arent always localized and can happen thousands of miles from the epicenter. An effective tsunami warning system relies on the free and open exchange and long-term management of global data and science products to mitigate, model, and forecast tsunamis. Read more from USGS: The Great Alaska Earthquake and Tsunami of March 27, 1964, Teachers' questions: The quake that shook up geology. She now estimates that it takes at least 500 years of plate motion to set the stage for such big earthquakes. Thats where one tectonic plate sinks beneath another. In places, the waves towered as high as a 20-story building. 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. Convergent (Colliding): This occurs when plates move towards each other and collide. The Sierra Nevada are the eroded remnants of the volcanic arc developed when the Farallon Plate subducted beneath the continent. Policies and Notices, U.S. Department of the Interior | Faults are fractures in Earths crust where movement has occurred. Another form of convergent boundary is a collision where two continental plates meet head-on. NS = National Seashore Plafkers team mapped all the changes triggered by the quake that they could find. That is where the plates push into, against or away from each other. Oral presentations, poster sessions, exhibits, field trips, business meetings and social gatherings all provide participants the opportunity to meet and share with their peers. The .gov means its official. Alaskas continental shelf and North American plate rose over 9 meters during the earthquake. The megathrust boundary between the plates results in both the 4,000-km-long Aleutian Trench and in the arc of active volcanoes that lie subparallel to the trench. Explains how Yakutat terrane accretion drives mountain building and crustal fault earthquakes like the 2002 M7.9 Denali Earthquake. What type of plate boundary causes earthquakes in Alaska? These cracks generally ran at high angles to the faults and could run a few hundred feet and span 6 inches (15 centimeters). Point Reyes National Seashore and Golden Gate National Recreation Area are the only two NPS sites that are right on the San Andreas Fault. Learn about the Great Alaska Earthquake of 1964 in this video adapted from the Valdez Museum & Historical Archive. N Pres = National Preserve. The southern edge of our state is an active tectonic plate boundary where the Pacific plate subducts (i.e., dives beneath) the North American plate along the great Alaska-Aleutian Megathrust. For more information on how you can prepare for a tsunami, visit the National Tsunami Hazard Mitigation Program. Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute. Downtown Anchorage had the most property damage mainly due to immense landslides, one of which dropped the business district nine feet. It includes many lesser faults in addition to the San Andreas Fault. It was the first global seismic network, West tells Science News for Students. The demolished towns of Valdez and Chenega were rebuilt on higher ground, but not everyone was prudent about rebuilding on earthquake-prone land. Sign up for the Academys monthly newsletter and get a promo code for 10% off at our online retail store. The epicenter is that X-marks-the-spot site where the tremors commenced. That movement generated huge and fast-moving waves in the open ocean, called tsunamis. Finally, the pressure between the plates is so great that they break loose. Transform plate boundaries produce enormous and deadly earthquakes. USC Tsunami Research Group.The Great M9.2 Alaska Earthquake and Tsunami of March 27, 1964. You'll be happy you did. The islands contain sedimentary layers and pillow lavas that formed on the ocean floor. The earthquake must be a shallow marine event that displaces the seafloor. On the east, the North American Plate is subducting westward, forming volcanoes of the Lesser Antilles Island Arc. NP = National Park 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. Earths big breakup. Science News for Students. National Park Service Sites (shown in red) Copalis River, Washington Trees along the Washington coast were killed by salt-water invasion when the land suddenly dropped during the last great Cascadia Subduction Zone earthquake . This post is part of Exploring Earthquakes, a rich collection of resources co-presented by the California Academy of Sciences and KQED. Although the school was destroyed, the nearby water tower was undamaged. From Montague Island, the faults and related belt of maximum uplift may extend southwestward on the Continental Shelf to the vicinity of the Kodiak group of islands. At transform boundaries lithosphere is neither created nor destroyed. The collision of tectonic plates can result in earthquakes, volcanoes, the formation of mountains, and other geological events. Ground subsidence due to the earthquake created a huge, deep ditch (a graben) that ran through the yard and under this house in Anchorage. In bays and inlets, the quake also triggered underwater landslides. This 3-panel image shows a simplified representation of a tsunami-generating earthquake cycle on the Alaska-Aleutian Megathrust. Deployment of tools like deep ocean pressure sensors (Deep-ocean Assessment and Reporting of Tsunamis or DART) are designed to ensure early detection of tsunamis and acquire data critical to real-time forecasts. The purpose of the group is to bring together both institutions and individuals who have an interest in reducing earthquake hazards in Alaska. Lucky for this team, 70 new seismographs (SIZE moh grafs) had recently been installed all over the world. Geological surveys taken immediately afterward showed parts of the Alaskan coast sank up to eight feet, other parts rose up to 38 feet and much of the coast moved 50 feet towards the ocean. Produced by Creative Arts Studio in 1964 for the USGS. UAF is an AA/EO employer and educational institution and prohibits illegal discrimination against any individual: If you have difficulty accessing the information on this website due to a disability, please contact the web administrator by email at uaf-aec@alaska.edu or by phone at 907-474-7320. To the north and northwest of the zone of uplift, subsidence forms a broad asymmetrical downwarp centered over the Kodiak-Kenai-Chugach Mountains that averages 2 feet and attains a measured maximum of 7 feet along the southwest coast of the Kenai Peninsula. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . In some cases, however, a convergent plate boundary can result in one tectonic plate diving underneath another. When the ground dropped 3 feet, the trees shallow roots ended up in the tidal zone. That will give you an idea of how fast the plates move relative to one anotherabout a fraction of an inch to a few inches per year! Imagine that your left hand is the undeformed Pacific Plate, your right hand the intact North American Plate. There, in California, that motion causes earthquakes along the infamous San Andreas Fault. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely. The quake also led to significant scientific breakthroughs in subduction earthquakes and how to minimize their destruction. Plate boundaries are found at the edge of the lithospheric plates and are of three types, convergent, divergent and conservative. Uplift that averages 6 feet over broad areas occurred mainly along the coast of the Gulf of Alaska, on the adjacent Continental Shelf, and probably on the continental slope. The divergent boundary occurs when two tectonic plates move away from each other. It caused extensive damage to the city, including fires that lasted for several days, and killed an estimated 3,000 people. Along other, divergent boundaries, plates move away from each other. UAF is an AA/EO employer and educational institution and prohibits illegal discrimination against any individual: If you have difficulty accessing the information on this website due to a disability, please contact the web administrator by email at uaf-aec@alaska.edu or by phone at 907-474-7320. The delta slump triggered a local tsunami which destroyed almost anything left standing and ruptured the Union Oil Companys oil tanks, igniting a massive fire. Photo by Robert J. Lillie. The three main types of plate movements include: Divergent (Spreading):This is where two plates move away from each other. The Earthquake Trail at Point Reyes weaves back and forth across the fault line. 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. These quakes at transform faults are shallow focus. 1964 Alaskan Tsunami. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such . Sign up for event updates and exciting announcements. 345 Middlefield Road, MS 977 These occur directly along subduction zones. When oceanic and continental plates meet, the denser oceanic plate moves under the less dense continental plate. 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. Its a well-documented certainty. The earthquake hit at 3:11 pm approximately 100 miles (160 km) off the coast of Chile . In the Turnagain Heights area of Anchorage, soil liquefaction (when the ground behaves like a liquid) triggered a landslide which moved parts of a suburban bluff 2,000 feet into the bay, taking up to 75 homes with it. They tend to subtly creep along. tsunami One or many long, high sea waves caused by an earthquake, submarine landslide or other disturbance. U.S. Geological Survey Professional Paper 1527, Feature labels. Plafker named this event a megathrust earthquake. A reverse fault, like the Cascadia subduction zone off the coast of Oregon and Northern California (north of Mendocino California), has relatively deep earthquakeslike the 1964 Alaska earthquake and the 2004 But its interesting to note that this region is so heavily populated because of the same tectonic forces that sometimes shake it up with such violent consequences during earthquakes. Which of the following measures an earthquake's intensity based on the observed effects on people and structures? Scientists learned a lot from data gathered after the 1964 Alaskan earthquake and put the knowledge to good use. At 5:36 p.m. on March 27, 1964Good Fridaythe earth trembled just as many Alaskans were sitting down to dinner. The Great Rift Valley in Africa, the Red Sea and the Gulf of Aden all formed as a result of divergent plate motion. The rocks pulled down under the continent begin to melt. All rights reserved. UA is committed to providing accessible websites. You should receive your promo code shortly. Another form of convergent boundary is a collision where two continental plates meet head-on. Which type of boundaries can produce earthquakes at which produces the largest earthquakes? Map showing plate boundaries that were active during the 1964 Great Quake. Volcanic eruptions and shallow earthquakes are common where plates rip apart. Strong, destructive earthquakes can accompany a rapid, several-meter uplift of bedrock along subduction zones. This vehicle illustrates the force of the tsunami waves that had struck this truck, which had been 32 feet (9.8 meters) above sea level at the time of the quake. 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. Sometimes tectonic activity just shifts large portions of Earths surface, thrusting upward some portions along a fault. This type of knowledge helps us better design and site infrastructure, and develop disaster preparedness plans so that our families and communities are less at risk when earthquakes do strike. Credit: Photo Courtesy of Robert J. Lillie. The 1964 Alaska Earthquake taught coastal citizens to run for higher ground at the first sign of strong tremors. It extends across the two zones from the chain of active volcanoes in the Aleutian Range and Wrangell Mountains probably to the Aleutian Trench axis. W.R. Hansen/USGS, 1964 Alaska quake files. These tectonic plates move gradually, bumping and grinding against each other. But Alaskas 1964 Great Quake led to a huge leap in their understanding. . All rights reserved. An offset fence line reveals the 16 feet (5 meters) of lateral ground breakage that occured as the San Andreas Fault suddenly let loose during the 1906 San Francisco Earthquake. But if you see something that doesn't look right, click here to contact us! As the plates move past each other, they sometimes get caught and pressure builds up. This motion causes earthquakes. thrust fault boundary The 1964 Alaska earthquake resulted from rupture along the thrust fault boundary bet- ween the downgoing Pacific Plate and the overriding North American Plate, causing widespread shaking and tectonic defor- mation. Ned Rozells personal account of his meeting with George Plafker, one of three USGS Geologists who responded to the Alaska quake a few days after event. This is an earthquake. Remove unwanted regions from map data QGIS. OfficeEarthquake Science Center This can lead to the formation of huge, high mountain ranges such as the Himalayas. 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. These instruments detect and record earthquakes. Here, that 11-foot (3.4 meter) drop or subsidence took a line of parked cars with it. What boundary was the 1964 Alaska earthquake? This material is also available as a free iBooks textbook and iTunes U course. At this boundary, the Pacific Plate slides beneath the North American Plate, causing the majority of Alaska's earthquakes, including the 1964 earthquake. This uplift attained a measured maximum on land of 38 feet in a northwest-trending narrow belt less than 10 miles wide that is exposed on Montague Island in southwestern Prince William Sound. What type of fault caused the 1964 Alaska Earthquake? This is called subduction. The friction between these massive plates means they dont move fast. Evidence for progressive coastal submergence in the deformed region for several centuries preceding the earthquake, in combin1ation with transverse horizontal shortening indicated by the retriangulation data, suggests pre-earthquake strain directed at a gentle angle downward beneath the arc. The water drove a long, 2-by-6-inch-wide plank through a trucks 10-ply tire. The 1964 earthquake was the first time people understood that there were places called subduction zones that produce these really enormous earthquakes. The theory of plate tectonics is a relatively new scientific concept.

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