1946 Aleutian Islands earthquake
The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1. The shock had a moment magnitude of 8.6 and a maximum Mercalli intensity of VI. It resulted in 165 -- over $26 million in damage; the seafloor along the fault was elevated, triggering a Pacific-wide tsunami with multiple destructive waves at heights ranging from 45–130 ft. The tsunami obliterated the Scotch Cap Lighthouse on Unimak Island, Alaska among others, killed all five lighthouse keepers. Despite the destruction to the Aleutian Island Unimak, the tsunami had an imperceptible effect on the Alaskan mainland. Waves traveled across the ocean at 500 miles an hour and measured 55 feet high, crest to trough, according to the USGS; the wave reached Kauai, Hawaii 4.5 hours after the quake, Hilo, Hawaii 4.9 hours later. In Hilo, the death toll was high: 173 were killed, 163 injured, 488 buildings were demolished and 936 more were damaged. Witnesses told of waves inundating streets and storefronts. Many victims were swept out to sea by receding water.
The tsunami caused a lot of damage in Maui as well. Waves there demolished many other buildings; the residents of these islands were caught off-guard by the onset of the tsunami due to the inability to transmit any warnings from the destroyed posts at Scotch Cap, the tsunami is known as the April Fools Day Tsunami in Hawaii because it happened on April 1st and many people thought it to be an April Fool's Day prank. The effects of the tsunami reached the West Coast of the United States; the tsunami was unusually powerful for the size of the earthquake. The event was classified as a tsunami earthquake due to the discrepancy between the size of the tsunami and the low surface wave magnitude; the large-scale destruction prompted the creation of the Seismic Sea Wave Warning System, which became the Pacific Tsunami Warning Center in 1949. List of earthquakes in 1946 List of earthquakes in Alaska List of earthquakes in the United States Tsunami 1946 – Hilo on YouTube Tsunami Animation: Unimak Island, Aleutian Islands, 1946 – Pacific Tsunami Warning Center 1946 Aleutians Tsunami – Western States Seismic Policy Council Mystery of Deadly 1946 Tsunami Deepens – LiveScience The International Seismological Centre has a bibliography and/or authoritative data for this event
1899 Yakutat Bay earthquakes
During September 1899 there was a series of severe earthquakes in the region around Yakutat Bay in Alaska. The most powerful of these occurred on September 10 at local time; the area was sparsely populated and no fatalities were recorded, but the earthquakes were notable for the degree of elevation recorded, up to 47 feet, for the effects on the glaciers in the region. Fieldwork on the effects of the earthquake was carried out between 1905 and 1910, a summary report was published in 1912 The most dramatic accounts came from a group of prospectors whose camp was close to a glacial stream about a mile SE of the ice cliff of Hubbard Glacier. After the initial shock on the morning of September 10, they rigged up a seismograph using dangling knives, counted 52 shocks before the most powerful shock occurred at noon; this was strong enough that the men could not stand, some of them avoided being thrown about by holding on to the tent pole. The shock lasted several minutes, with the ground shaking like the swell of the sea.
There was a lake above the camp, which burst its bank due to the shock, deluged the site of the camp with water and debris. Shortly after this a wave of water 20 feet high came in from the sea. One can imagine the men running for their lives while not knowing which way to turn, but all escaped to the higher ground, though losing most of their provisions. After things had calmed down they returned to the campsite to find that one of their boats had survived intact; the next morning they found an empty damaged native canoe that they were able to repair, with the two boats were able to make their way to the small settlement of Yakutat. This took several days; when they reached Yakutat they found the place empty, the whole village camped out on the hill behind the village. Field investigations by members of the US Geological Survey in subsequent years found evidence of substantial changes in ground level in the affected areas uplift; the evidence was of several types: physiographic, such as elevated sea-cliffs, sea-caves, beaches as well as new reefs and islands.
Taken together they found evidence for uplift of up to 47 feet. This is more than had been reported up to that date The immediate effect of the earthquake on the glaciers of the Yukutat Bay region was shattering of the ice at the margins of the glaciers; this led to a release of many icebergs and to the formation of deep crevasses, which made traverse of the ice impossible in areas, passable. Longer-term effects noted in the fieldwork were substantial advances in many of the icebergs close to the earthquake zone. Tarr and Martin attribute this to earthquake-induced avalanches in the mountainous areas above the glaciers leading to an increase in the snow and ice deposited on the upper parts of the glacier; this additional load would work is way down the track of the glacier over a period of years. By contrast, Muir Glacier, about 100 miles SE of Yakutat Bay, receded in the years after the earthquake; the reasons for this are less clear. The earthquake was felt up to 250 miles from the centre of activity, there were reports from up to 700 miles away that may have been of the same earthquake or of associated shocks.
Seismographs throughout the world recorded the earthquake of September 10, as well as the earlier and shocks during September. Records show that the time of the heaviest shock on September 10 was 12:22 pm local solar time, equivalent to 21:40:13 UTC; the magnitude of the earthquake has been estimated at 8.0, the approximate location of the epicentre was 60 deg north, 140 deg west
2018 Anchorage earthquake
On November 30, 2018, at 8:29 a.m. AKST, a magnitude 7.1 earthquake hit South Central Alaska. The earthquake's epicenter was near Joint Base Elmendorf–Richardson, about 10 miles north of Anchorage, occurred at a depth of 29 miles, it was followed six minutes by a magnitude 5.7 aftershock centered 2.5 miles north-northwest of the municipality. The earthquake could be felt as far away as Fairbanks; the National Tsunami Warning Center—itself located inside the quake zone, in Palmer, Alaska, 42 miles northeast of Anchorage—issued tsunami warnings for nearby coastal areas, including Cook Inlet and the Kenai Peninsula, but they were lifted shortly after. Southern Alaska lies at the eastern end of the Aleutian Trench, where the Pacific Plate is subducting beneath the North American Plate. Near Anchorage, the plates are converging at a rate of 57 mm per year; the region has experienced severe earthquakes including several megathrust earthquakes. The 1964 earthquake, with a magnitude of 9.2, was the largest earthquake in American history and the second largest to be recorded anywhere in the world.
Though earthquakes are common in Alaska, they occur out at sea. This earthquake is more similar to the 2001 Nisqually earthquake located near Tacoma, than to the 1964 megathrust earthquake; the earthquake had a magnitude of 7.1 on the moment magnitude scale using a centroid moment tensor inversion of the W-phase. The focal mechanism shows. A fault dipping at 29° towards the east gives the best match to the observed seismic waveforms; the depth and mechanism are consistent with faulting within the down-going Pacific Plate. This implies that the earthquake was an intraslab earthquake within that plate, rather than at the plate boundary between the Pacific and North American Plates beneath the Anchorage area; this is a different mechanism than megathrust faults in the region, which do occur on the plate boundary itself. This faulting in the Pacific Plate is caused by downward bending while the plate is being forced under Alaska. Over 80 aftershocks of various magnitudes were recorded throughout the day, with at least three having magnitudes greater than 5.0.
By December 3, 170 aftershocks with a magnitude over 3.0 had been noted. Two more aftershocks hit on February 6, the first with a magnitude of 4.1, the second coming 23 minutes with a magnitude of 3.7. Aftershocks were expected to continue for around 300 days after the mainshock. Severe damage to several buildings and a highway overpass near Ted Stevens Anchorage International Airport was reported. There were no casualties reported; the Kenai Peninsula Borough School District reported. Landings at four airports were temporarily affected by the earthquake: the Ted Stevens International Airport, Adak Airport, Merrill Field Airport and Joint Base Elmendorf–Richardson; the Anchorage Police Department reported major infrastructure damage across the city. Liquefaction was reported. Several traffic lights were knocked down. Many roads were damaged; the Glenn Highway was damaged to the point where officials stated it would take a long time to repair. A ramp connecting Minnesota Drive to area streets collapsed, as well as the surrounding hillside.
A driver in an SUV, on the section of destroyed highway was stranded, but uninjured. The Alaska Railroad had to suspend all operations due to severe damage at their operations center and unknown condition of tracks; the operators of the Trans-Alaska Pipeline shut the system down as a precaution. The newsroom studio of CBS-affiliate KTVA in Anchorage was damaged, but the channel remained on the air; the Alaska Airlines Center, a large sports complex on the University of Alaska Anchorage campus, flooded due to broken fire sprinkler pipes. Several trophy cases were damaged. UAA's older Wells Fargo Sports Complex suffered similar damage. In South Anchorage, Dimond High School had ceiling tiles and other debris littering the floor throughout the campus. Most schools in the Anchorage School District suffered damage. Along with Dimond High, Colony Middle, Colony High and Bartlett High School were heavily damaged. Colony Middle School suffered damage to ceiling tiles, water pipes, lights and was being evaluated for structural damage.
During the earthquake, a student suffered a broken wrist, a custodian was injured by breaking glass at area schools. Several branches in the Anchorage Public Library system sustained damage. Numerous books were knocked off the shelves. Structural damage was noted in some locations. In the Anchorage community of Eagle River, at least one home collapsed during the earthquake. One man in the home, whose spouse was at work, was able to escape with several pets. There was heavy damage in the Matanuska-Susitna Valley, north of Anchorage; the Matanuska-Susitna Borough School District reported that Houston Middle School, located in the town of Houston, was damaged and will not reopen during the current school year. Five other schools will take longer than a week to reopen. Colony middle school students were the last to get to go back to learning. Significant damage was done to roads in the Mat-Su. Among the most damaged roads were the Palmer-Wasilla Highway, Pittman Road, Point MacKenzie Road and Vine Road.
Suffering the worst damage was Vine Road, a section of which buckled and became impassable. In addition, Matanuska Electric Association reported that 46,000 customers were left without electricity after the earthquake. Overall, damage in Anchorage was estimated
1964 Alaska earthquake
The 1964 Alaskan earthquake known as the Great Alaskan earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday, March 27. Across south-central Alaska, ground fissures, collapsing structures, tsunamis resulting from the earthquake caused about 131 deaths. Lasting four minutes and thirty-eight seconds, the magnitude 9.2 megathrust earthquake remains the most powerful earthquake recorded in North American history, the second most powerful earthquake recorded in world history. Six hundred miles of fault ruptured at once and moved up to 60 ft, releasing about 500 years of stress buildup. Soil liquefaction, fissures and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses and infrastructure in the several landslide zones along Knik Arm. Two hundred miles southwest, some areas near Kodiak were permanently raised by 30 feet. Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet, requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.
In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks, inside the ship, docked there at the time. Nearby, a 27-foot tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there. Post-quake tsunamis affected Whittier, Seward and other Alaskan communities, as well as people and property in British Columbia, Washington and California. Tsunamis caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was reported from Florida and Texas. On March 27, 1964, at 5:36 p.m. AKST, a fault between the Pacific and North American plates ruptured near College Fjord in Prince William Sound; the epicenter of the earthquake was 12.4 mi north of Prince William Sound, 78 miles east of Anchorage and 40 miles west of Valdez. The focus occurred at a depth of 15.5 mi. Ocean floor shifts created large tsunamis, which resulted in many of the deaths and much of the property damage.
Large rockslides were caused, resulting in great property damage. Vertical displacement of up to 38 feet occurred, affecting an area of 100,000 square miles within Alaska. Studies of ground motion have led to a peak ground acceleration estimate of 0.14–0.18 g. The Alaska earthquake was a subduction zone earthquake, caused by an oceanic plate sinking under a continental plate; the fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. This caused much of the uneven ground, the result of ground shifted to the opposite elevation. Two types of tsunamis were produced by this subduction zone earthquake. There was a tectonic tsunami produced in addition to local tsunamis; these smaller tsunamis were produced by submarine and subaerial landslides and were responsible for the majority of the tsunami damage. Tsunami waves were noted in over 20 countries, including Peru, New Zealand, Papua New Guinea, Japan and Antarctica; the largest tsunami wave was recorded in Shoup Bay, with a height of about 220 ft. Tremors were detected in water wells in Australia.
As a result of the earthquake, 131 people are believed to have died: Nine died as a result of the earthquake itself, 122 died from the subsequent tsunami in places all around the world, five died from the tsunami in Oregon, 13 died from the tsunami in California. The quake was a reported XI on the modified Mercalli Intensity scale "indicating major structural damage, ground fissures and failures". Property damage was estimated at about $116 million, it is that the toll would have been much higher had the quake not occurred after 5 PM on Good Friday. Most damage occurred in Anchorage, 75 mi northwest of the epicenter. Anchorage was not hit by tsunamis, but downtown Anchorage was damaged, parts of the city built on sandy bluffs overlying "Bootlegger Cove clay" near Cook Inlet, most notably the Turnagain neighborhood, suffered landslide damage; the neighborhood lost 75 houses in the landslide, the destroyed area has since been turned into Earthquake Park. The Government Hill school suffered from the Government Hill landslide, leaving it in two jagged, broken pieces.
Land overlooking the Ship Creek valley near the Alaska Railroad yards slid, destroying many acres of buildings and city blocks in downtown Anchorage. Most other areas of the city were only moderately damaged; the 60-foot concrete control tower at Anchorage International Airport was not engineered to withstand earthquake activity and collapsed, killing William George Taylor, the Federal Aviation Agency air traffic controller on duty in the tower cab at the time the earthquake began. One house on W. 10th Avenue suffered peripheral damage, but only one block away the completed Four Seasons Building on Ninth Avenue collapsed with the concrete elevator shafts sticking up out of the rubble like a seesaw. The hamlets of Girdwood and Portage, located 30 and 40 mi southeast of central Anchorage on the Turnagain Arm, were destroyed by subsidence and subsequent tidal action. Girdwood was relocated inland and Portage was abandoned
2002 Denali earthquake
The 2002 Denali earthquake occurred at 22:12:41 UTC November 3 with an epicenter 66 km ESE of Denali National Park, United States. This 7.9 Mw earthquake was the largest recorded in the United States in 37 years. The shock was the strongest recorded in the interior of Alaska. Due to the remote location, there were only a few injuries. Due to the shallow depth, it was felt at least as far away as Seattle and it generated seiches on bodies of water as far away as Texas and New Orleans, Louisiana. About 20 houseboats were damaged by a seiche on a lake in Washington State; the Denali-Totschunda fault is a major dextral strike-slip system, similar in scale to the San Andreas fault system. In Alaska, moving from east to west, the plate interactions change from a transform boundary between Pacific and North American plates to a collision zone with a microplate, the Yakutat terrane, in the process of being accreted to the North American plate, to a destructive boundary along the line of the Aleutian islands.
The Denali-Totschunda fault system is one of the structures that accommodate the accretion of the Yakutat terrane. On October 23, 2002, there was a magnitude 6.7 earthquake located on the Denali fault. Because of its location close to the November 3 event and the fact that it preceded it by only 11 days, this earthquake is regarded as a foreshock that directly triggered the main shock; the initial rupture on November 3 was on a thrust fault segment, the unknown Susitna Glacier thrust, to the south of the Denali fault. The epicenter lies just 25 kilometers east of the October 23 foreshock; the rupture jumped to the main Denali Fault strand propagating for a further 220 km before jumping again onto the Totschunda Fault and rupturing another 70 km of fault plane. The total surface rupture was ca. 340 km. There is evidence of local supershear propagation inferred from ground motions. Minor damage was reported over a wide area but the only examples of severe damage were on highways that crossed the fault trace and areas that suffered liquefaction, e.g. Northway Airport.
Several bridges were damaged but none so that they were closed to traffic. Due to the general self-sufficiency of those living near the fault rupture few lifeline systems were compromised; these people tend to get water from private wells, heat their homes and cook their meals with gas furnaces and stoves, maintain individual septic systems. The Trans-Alaska Pipeline System crosses the rupture trace. There was no oil spillage, as the pipeline at that location was designed to move laterally along beams to withstand major movement on the Denali Fault; the pipeline was shut down for three days to allow for inspections but was reopened. List of earthquakes in 2002 List of earthquakes in Alaska List of earthquakes in the United States The 2002 Denali Fault earthquake – United States Geological Survey M 7.9 Denali Fault earthquake of November 3, 2002 – Alaska Earthquake Center The International Seismological Centre has a bibliography and/or authoritative data for this event
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration is an American scientific agency within the United States Department of Commerce that focuses on the conditions of the oceans, major waterways, the atmosphere. NOAA warns of dangerous weather, charts seas, guides the use and protection of ocean and coastal resources, conducts research to provide understanding and improve stewardship of the environment. NOAA was formed in 1970 and in 2017 had over 11,000 civilian employees, its research and operations are further supported by 321 uniformed service members who make up the NOAA Commissioned Corps. Since October 2017, NOAA has been headed by Timothy Gallaudet, as acting Under Secretary of Commerce for Oceans and Atmosphere and NOAA interim administrator. NOAA plays several specific roles in society, the benefits of which extend beyond the US economy and into the larger global community: A Supplier of Environmental Information Products. NOAA supplies to its customers and partners information pertaining to the state of the oceans and the atmosphere.
This is clear through the production of weather warnings and forecasts via the National Weather Service, but NOAA's information products extend to climate and commerce as well. A Provider of Environmental Stewardship Services. NOAA is a steward of U. S. coastal and marine environments. In coordination with federal, local and international authorities, NOAA manages the use of these environments, regulating fisheries and marine sanctuaries as well as protecting threatened and endangered marine species. A Leader in Applied Scientific Research. NOAA is intended to be a source of accurate and objective scientific information in the four particular areas of national and global importance identified above: ecosystems, climate and water, commerce and transportation; the five "fundamental activities" are: Monitoring and observing Earth systems with instruments and data collection networks. Understanding and describing Earth systems through research and analysis of that data. Assessing and predicting the changes of these systems over time.
Engaging and informing the public and partner organizations with important information. Managing resources for the betterment of society and environment. NOAA traces its history back to multiple agencies, some of which were among the oldest in the federal government: United States Coast and Geodetic Survey, formed in 1807 Weather Bureau of the United States, formed in 1870 Bureau of Commercial Fisheries, formed in 1871 Coast and Geodetic Survey Corps, formed in 1917Another direct predecessor of NOAA was the Environmental Science Services Administration, into which several existing scientific agencies such as the United States Coast and Geodetic Survey, the Weather Bureau and the uniformed Corps were absorbed in 1965. NOAA was established within the Department of Commerce via the Reorganization Plan No. 4 and formed on October 3, 1970 after U. S. President Richard Nixon proposed creating a new agency to serve a national need for "better protection of life and property from natural hazards …for a better understanding of the total environment… for exploration and development leading to the intelligent use of our marine resources."
In 2007, NOAA celebrated 200 years of service in its role as successor to the United States Survey of the Coast. In 2013, NOAA closed 600 weather stations. Since October 25, 2017 Timothy Gallaudet, Assistant Secretary of Commerce for Oceans and Atmosphere, has served as acting Under Secretary of Commerce for Oceans and Atmosphere at the US Department of Commerce and NOAA's interim administrator. Gallaudet succeeded Benjamin Friedman, who served as NOAA's interim administrator since the end of the Obama Administration on January 20, 2017. In October 2017, Barry Lee Myers, CEO of AccuWeather, was proposed to be the agency's administrator by the Trump Administration. NOAA works toward its mission through six major line offices, the National Environmental Satellite and Information Service, the National Marine Fisheries Service, the National Ocean Service, the National Weather Service, the Office of Oceanic and Atmospheric Research and the Office of Marine & Aviation Operations, and in addition more than a dozen staff offices, including the Office of the Federal Coordinator for Meteorology, the NOAA Central Library, the Office of Program Planning and Integration.
The National Weather Service is tasked with providing "weather and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy." This is done through a collection of national and regional centers, 13 river forecast centers, more than 120 local weather forecast offices. They are charged with issuing weather and river forecasts, advisories and warnings on a daily basis, they issue more than 734,000 weather and 850,000 river forecasts, more than 45,000 severe weather warnings annually. NOAA data is relevant to the issues of global warming and ozone depletion; the NWS operates NEXRAD, a nationwide network of Doppler weather radars which can detect precipitation and their velocities. Many of their products are broadcast on NOAA Weather Radio, a network of radio transmitters that broadcasts weather forecasts, severe weather statements and warnings 24 hours a day; the National Ocean Service focuses on ensuring that ocean and coastal areas are safe and productive.
NOS scientists, natural resource managers, specialists serve America by ensuring safe and efficient marine transportation, promoting innovative solutions to protect coastal communities, conserving mari
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, the natural hazards that threaten it; the organization has four major science disciplines, concerning biology, geography and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility; the USGS is a bureau of the United States Department of the Interior. The USGS employs 8,670 people and is headquartered in Reston, Virginia; the USGS has major offices near Lakewood, Colorado, at the Denver Federal Center, Menlo Park, California. The current motto of the USGS, in use since August 1997, is "science for a changing world." The agency's previous slogan, adopted on the occasion of its hundredth anniversary, was "Earth Science in the Public Service." Since 2012, the USGS science focus is directed at six topical "Mission Areas", namely Climate and Land Use Change, Core Science Systems, Ecosystems and Minerals and Environmental Health, Natural Hazards, Water.
In December 2012, the USGS split the Energy and Minerals and Environmental Health Mission Area resulting in seven topical Mission Areas, with the two new areas being: Energy and Minerals and Environmental Health. Administratively, it is divided into six Regional Units. Other specific programs include: Earthquake Hazards Program monitors earthquake activity worldwide; the National Earthquake Information Center in Golden, Colorado on the campus of the Colorado School of Mines detects the location and magnitude of global earthquakes. The USGS runs or supports several regional monitoring networks in the United States under the umbrella of the Advanced National Seismic System; the USGS informs authorities, emergency responders, the media, the public, both domestic and worldwide, about significant earthquakes. It maintains long-term archives of earthquake data for scientific and engineering research, it conducts and supports research on long-term seismic hazards. USGS has released the UCERF California earthquake forecast.
As of 2005, the agency is working to create a National Volcano Early Warning System by improving the instrumentation monitoring the 169 volcanoes in U. S. territory and by establishing methods for measuring the relative threats posed at each site. The USGS National Geomagnetism Program monitors the magnetic field at magnetic observatories and distributes magnetometer data in real time; the USGS collaborates with Canadian and Mexican government scientists, along with the Commission for Environmental Cooperation, to produce the North American Environmental Atlas, used to depict and track environmental issues for a continental perspective. The USGS operates the streamgaging network for the United States, with over 7400 streamgages. Real-time streamflow data are available online. National Climate Change and Wildlife Science Center implements partner-driven science to improve understanding of past and present land use change, develops relevant climate and land use forecasts, identifies lands and communities that are most vulnerable to adverse impacts of change from the local to global scale.
Since 1962, the Astrogeology Research Program has been involved in global and planetary exploration and mapping. In collaboration with Stanford University, the USGS operates the USGS-Stanford Ion Microprobe Laboratory, a world-class analytical facility for U--Pb geochronology and trace element analyses of minerals and other earth materials. USGS operates a number of water related programs, notably the National Streamflow Information Program and National Water-Quality Assessment Program. USGS Water data is publicly available from their National Water Information System database; the USGS operates the National Wildlife Health Center, whose mission is "to serve the nation and its natural resources by providing sound science and technical support, to disseminate information to promote science-based decisions affecting wildlife and ecosystem health. The NWHC provides information, technical assistance, research and leadership on national and international wildlife health issues." It is the agency responsible for surveillance of H5N1 avian influenza outbreaks in the United States.
The USGS runs 17 biological research centers in the United States, including the Patuxent Wildlife Research Center. The USGS is investigating collaboration with the social networking site Twitter to allow for more rapid construction of ShakeMaps; the USGS produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, areas of Alaska near Anchorage and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles.
At 49° north latitude, 49 square miles are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale requires a separate and specialized romer scale for pl