First of three parts
Travelers on the busy Seward Highway motor past a "ghost forest" of dead, slumped-over trees killed when saltwater rushed in after the land along Turnagain Arm dropped by as much as 10 feet.
The former townsite of Portage along the highway, home to 71 people in 1960, is now only a trio of mostly collapsed wooden structures and at least one rusty truck skeleton. In west Anchorage, visitors to Earthquake Park can stand on a steep overlook carved from the bluff when blocks of earth split away.
In other places, the earthquake thrust land upward or moved it sideways. Outer areas in Prince William Sound, near the quake's epicenter, were thrust up more than 25 feet. Middleton Island was raised so high that a dock there that was once a stopping place for mariners was raised far uphill and rendered useless. Islands moved sideways as well -- nearly 60 feet to the southeast.
Those and other obvious physical changes are more than reminders of tragedy. They helped change the world of science and the understanding of Earth's dynamics.
Prior to March 27, 1964, the concept of plate tectonics was just a theory, though one that was gradually gaining acceptance among scientists. The Great Alaska Earthquake confirmed that theory, said geologist Peter Haeussler, the U.S. Geological Survey's Alaska earthquake-hazards coordinator.
"It was only after the '64 earthquake that it made sense," Haeussler said.
Origins of plate tectonics
Fifty years ago, geologists and non-scientists alike understood that earthquakes occur along known fault lines where sections of earth rub against each other. Those events -- like the 1906 San Francisco quake -- leave clear cracks in the ground, sometimes visible over long distances. Haeussler likens them to cracks that appear on the top of a bent chocolate bar.
But the world's most powerful quakes, scientists have learned since 1964, are subduction events in which one tectonic plate slips under another, Haeussler said.
The origins of tectonic plate theory date back to the end of the 16th century, when cartographers noticed that the edges of South America and Africa fit together. A few navigators from that era also noticed that the sea floor had varying depths and was not flat.
For a long time, Haeussler said, scientists embraced a theory that the Earth is expanding and that the form and location of the continents -- and the occurrence of earthquakes -- were products of this inflation.
Alfred Weneger in the early 20th century articulated the theory of continental drift -- the idea that continents once stuck together were pulled apart by geologic force. Weneger hypothesized that the continents moved across the sea floor by plowing their own paths over the Earth.
Weneger's theory was not easily accepted, partly because he was a German living in an era -- including World War I -- when German ideas were considered suspect, Haessler said.
U.S. seismologist Hugo Benioff in midcentury found indication, from seismic waves emitted by earthquakes, that there were plates that were sloping downward.
But it took a couple of decades before the specific theory of tectonic plates was expressed, Haeussler said. That came from geologist and U.S. Navy Admiral Harry Hess, who hypothesized that continents travel on moving tectonic plates. He authored an important paper, released in 1962, that described what he believed was the link between tectonic plates and the spread of the seas' floors.
"Part of it was speculation, but it was really informed speculation by a really smart guy," Haeussler said.
Alaska's plate tectonics expert
The next really smart guy on the scene was George Plafker. Plafker, dispatched to Alaska in 1964 to study the sudden land changes, is still working at the USGS and is scheduled to be in Anchorage for events commemorating the earthquake. Plafker and his USGS colleagues surveyed the damage and pieced together the plate movements that caused the earthquake. Since 1964, he has emerged as one of the world experts on plate tectonics.
Along with creating better understanding of modern seismic events, the 1964 disaster gave scientists insight into powerful prehistoric quakes, Haeussler said.
Middleton Island, for example, has a series of terraces created as the land was pushed up by successive prehistoric subduction earthquakes. Along Turnagain Arm, beyond the ghost trees and occasional wrecked 1964-era building, people can dig into earth and find older peat and silt layers created by those prehistoric events, Haeusssler said.
Human toll could have been higher
While the possible human casualties from the prehistoric subduction earthquakes are unknown, 132 deaths are attributed to the 1964 earthquake and the tsunamis that followed. The vast majority of those killed perished in coastal towns where tsunamis swept in. The toll reached beyond Alaska: four people were killed in Oregon and 13 in California, according to NOAA records.
Still, the losses were not as bad as they could have been, thanks to Alaska's sparse population at the time. The 1960 census lists Alaska's total population at 226,167 -- about one-third of today's estimated population of 735,132. Growth and the spread of development across Alaska and the U.S. West Coast might mean more vulnerability next time, if there is a next time, scientists say.
A USGS study released last year considered likely impacts to California if a similarly powerful quake were to happen today in a slightly different part of the Gulf of Alaska. The study, conducted in collaboration with California agencies, focused on direct economic losses, which it estimated to be up to $6 billion in the state. Though the study did not focus on human casualties, it noted that there would be "substantial loss of life" in California should a magnitude 9.1 quake strike off the Alaska Peninsula.
Read Part 2: In Great Alaska Earthquake, most deaths were caused by tsunamis
Read Part 3: 50 years later, earthquake-inspired building moratorium expiring at old Valdez
Contact Yereth Rosen at yereth(at)alaskadispatch.com.