My earliest memories of earthquakes involve watching the ensuing evacuation of downtown Sitka as people hurried to Sitka High, one of the highest refuges in town. Our house was situated on a high hill, and we could stay there and observe, safely above the land that the feared Tsunami would wash over. This was the early 1980's and the memory of the 1964 Quake must have still been fresh in everyone's minds. I always pictured that wave coming in as a giant wall of water, and only recently learned that it would have probably arrived as more of a monster high tide.
The 1964 earthquake was the last major earthquake that occurred in Southern Alaska. It was a 9.2 on the Richter Scale, making it the second largest quake in recorded history, and lasted for more than 4 minutes. It caused devastating damage in many Alaskan communities, including Anchorage, Valdez, and Seward. The quake was caused by plate tectonics, with the more dense Pacific Plate subducting beneath the North American Plate. Earthquakes are caused when pressure is released by the two plates sliding past each other. Southern Alaska has lots of little earthquakes caused by this process, and you can see the latest earthquakes by using the Real-time Earthquakes plugin found on Google Earth.
The Latest Earthquakes in Alaska, as seen on Google Earth, 2/21/10 - 1:59 pm
These little earthquakes actually help keep us safe. Seismologists start to worry when there is a respite from quakes anywhere along our tectonic plate boundary, because it means that pressure is building up, and the more pressure released in an earthquake, the bigger it is. In the case of the 1964 Quake, the released pressure allowed the N. American plate to rebound up about 9 meters underneath the ocean, and caused a large open ocean waves, or Tsunami. Underwater landslides in the bays of fjords also triggered local waves that did much to damage coastal communities.
Earthquakes originate at the point where pressure between the plates is released, which is called the epicenter. The first waves to leave the epicenter are the primary, or P waves. These look kind of "centipedy", moving like sound waves by compacting and extending. We can sense these waves, but they don't do much damage. The secondary, or S waves, that follow are much more damaging, as they move more sinuously, up and down and side to side. Together P and S waves cause surface waves, which make the ground undulate as if it were the ocean and tear buildings to pieces. Early warning systems are being designed that can be used in some areas, such as the San Andreas Fault, to detect the P waves and give up to 10-15 seconds of warning before the damage starts. This doesn't seem like much, but even a little time allows transportation systems to begin to slow and stop, greatly reducing the damage that could be caused.
This phenomenon is apparent along the northern boundary of the Pacific Plate, where it dives back down into the mantle, forming the Aleutian Trench, and subsequently the Aleutian Archipelago showing direct cause and effect. The Aleutian Archipelago consists of 300 mostly volcanic islands, and has at least 57 active volcanoes. These volcanoes can be explored through a great interactive site found on Teachers Domain.
Volcanoes can occur in the middle of tectonic plates as well, as shown by the Hawaiian Island Emporer Seamount Chain. This is believed to be caused by a "hot spot" underneath the Pacific plate, where superheated rock rises. As the Pacific Plate moves northward a few cm per year over this "hot spot" new volcanic islands are formed. In fact, a new volcanic island, Loihi, is building up beneath the ocean and is set to emerge in the next several thousand years.
It is important that today's students learn about cataclysmic events because society needs to continue to be plan for them happening, and be prepared when they do. This is easier to do in Southern Alaska, because we have evidence of the subduction zone all around us. However, not all students here grow up in coastal villages, hearing stories from elders about past tsunamis and quakes, or even watching the town evacuate after every earthquake as I did. It is easy to forget the past, even in Anchorage, where buildings disintegrated and half of 4th avenue dropped ten feet. Large houses and even high rises are being built atop the Bootlegger Cove clay west of C street. In the next large quake this clay will liquify and shake like jello, and some structures may even slide into Cook Inlet as they did in 1964. Schools no longer practice earthquake drills, which have been supplanted by the more exciting "stay put" and "lockdown" drills that deal with armed intruders.
As teachers we need to make sure that students receive the education about cataclysmic events that they might not be receiving from their families, tv shows, and favorite internet sites. Easy activities, such as squeezing toothpaste up through a slowly moving screen, can show students how the Pacific "hot spot" is creating the Hawaiian Islands. Technology such as Google Earth and Youtube can bring these events into the classroom and make them exciting and real for students. Google Earth can be used to show simple cause and effect with plate boundaries and the real time earthquakes plugin. Students can use the measuring tool to show that the Aleutian Archipelago mirrors the Aleutian trench, and then learn about specific volcanoes using the interactive Teachers Domain site mentioned above. They can complete an inquiry activity where they watch the amazing Youtube video of the 1958 Lituya Bay Tsunami (told by the fisherman and his son that rode the wave and survived) and use Google Earth to see what evidence of the Tsunami can be found, and to try to determine what caused the event.
The more our students know about cataclysmic events, the better our society will be able to predict and respond to cataclysmic events. Our culture lives in a subduction zone replete with earthquakes, tsunamis, and volcanic eruptions, and like cultures in the past we either need to adapt, migrate, or perish. I vote for adapting.
Earthquakes originate at the point where pressure between the plates is released, which is called the epicenter. The first waves to leave the epicenter are the primary, or P waves. These look kind of "centipedy", moving like sound waves by compacting and extending. We can sense these waves, but they don't do much damage. The secondary, or S waves, that follow are much more damaging, as they move more sinuously, up and down and side to side. Together P and S waves cause surface waves, which make the ground undulate as if it were the ocean and tear buildings to pieces. Early warning systems are being designed that can be used in some areas, such as the San Andreas Fault, to detect the P waves and give up to 10-15 seconds of warning before the damage starts. This doesn't seem like much, but even a little time allows transportation systems to begin to slow and stop, greatly reducing the damage that could be caused.
Plate boundaries are also the home to volcanoes, which are caused by the upwelling of superheated rock, or magma. As a subducting plate delves into the earth's crust it is reheated, and rises back up to the surface, creating a volcano.
The Ring of Fire - where volcanoes and plate boundaries overlap
The Ring of Fire - where volcanoes and plate boundaries overlapVolcanoes can occur in the middle of tectonic plates as well, as shown by the Hawaiian Island Emporer Seamount Chain. This is believed to be caused by a "hot spot" underneath the Pacific plate, where superheated rock rises. As the Pacific Plate moves northward a few cm per year over this "hot spot" new volcanic islands are formed. In fact, a new volcanic island, Loihi, is building up beneath the ocean and is set to emerge in the next several thousand years.
It is important that today's students learn about cataclysmic events because society needs to continue to be plan for them happening, and be prepared when they do. This is easier to do in Southern Alaska, because we have evidence of the subduction zone all around us. However, not all students here grow up in coastal villages, hearing stories from elders about past tsunamis and quakes, or even watching the town evacuate after every earthquake as I did. It is easy to forget the past, even in Anchorage, where buildings disintegrated and half of 4th avenue dropped ten feet. Large houses and even high rises are being built atop the Bootlegger Cove clay west of C street. In the next large quake this clay will liquify and shake like jello, and some structures may even slide into Cook Inlet as they did in 1964. Schools no longer practice earthquake drills, which have been supplanted by the more exciting "stay put" and "lockdown" drills that deal with armed intruders.
As teachers we need to make sure that students receive the education about cataclysmic events that they might not be receiving from their families, tv shows, and favorite internet sites. Easy activities, such as squeezing toothpaste up through a slowly moving screen, can show students how the Pacific "hot spot" is creating the Hawaiian Islands. Technology such as Google Earth and Youtube can bring these events into the classroom and make them exciting and real for students. Google Earth can be used to show simple cause and effect with plate boundaries and the real time earthquakes plugin. Students can use the measuring tool to show that the Aleutian Archipelago mirrors the Aleutian trench, and then learn about specific volcanoes using the interactive Teachers Domain site mentioned above. They can complete an inquiry activity where they watch the amazing Youtube video of the 1958 Lituya Bay Tsunami (told by the fisherman and his son that rode the wave and survived) and use Google Earth to see what evidence of the Tsunami can be found, and to try to determine what caused the event.
The more our students know about cataclysmic events, the better our society will be able to predict and respond to cataclysmic events. Our culture lives in a subduction zone replete with earthquakes, tsunamis, and volcanic eruptions, and like cultures in the past we either need to adapt, migrate, or perish. I vote for adapting.
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