Alaskan Geology and The 1964 Earthquake

Prince William Sound glacier

When speaking of Alaska as a physical place, as a raw and textured landscape replete with massive ranges, volcanoes, and mountain-studded coastline, it’s important to remember that it lies along the Ring of Fire at the boundary of the Pacific and North American tectonic plates. If not for that fact, Alaska would be an entirely different sort of place. It would certainly be less dangerous, and maybe therefore less alluring. Mountain climbers would not flock here to tackle the continent’s highest peaks. Few would find reason to hop a ferry up its vast shores from town to town, exploring the tall fingers of coast on Prince William Sound or the glaciated bays along the Gulf of Alaska. Possibly, the fish would find its rivers less hospitable, and so too would the fishermen. In short, a different breed of wanderers, if any at all, would find themselves dreaming of the inimitable beauty of the Far North and seeking adventure here.

So, because Alaska has turned out to be the sort of place it is, we’d like to delve for a moment into the geologic drama that has shaped it and ultimately brought us here.

Bush plane in Denali

Alaska is essentially an immense mosaic. The accretion of its myriad pieces was and still is driven by plate tectonics, wherein the Pacific plate, like a vast and insistent conveyor belt, thrusts into the North American plate, compressing and folding the lands together to form a slew of valleys and ranges from the Brooks to the Alaskan and Chugach, to name a few. These pieces–once islands, chunks of ocean floor, bits broken off from other lands, and volcanic excretions–came together over the course of hundreds of millions of years of slow collision.

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It’s that process that drew Denali, North America’s tallest peak at 20,320 feet, skyward and continues to do so by a millimeter per year. Because it is composed mainly of granite unlike its older sedimentary neighbors (once submerged in ocean waters,) it’s much more resistant to weathering, giving it that striking 18,000-foot relief from base to summit–greater than Everest, K2, or Aconcogua. The Denali region is also rife with volcanic rock, as seen in the variegated slopes of Polychrome Pass.

Denali National Park

Outside of old stones in Denali and elsewhere in the interior, though, Alaska’s volcanism is still very active. Many volcanoes have erupted this year. Volcanoes exist almost exclusively on the coast as a result of subduction, which creates heated magma chambers at the plate’s edge. These same tectonic forces are responsible for earthquakes. Most are small and go unnoticed, but they’re occasionally devastating, like the infamous temblor of half a century ago.

Cordova harbor

At 5:36 PM on March 27, 1964–the evening of Good Friday–a magnitude 9.2 earthquake struck near Valdez, violently shaking all the coastal towns along Prince William Sound and the Kenai Peninsula on up to Anchorage. Everyone in Alaska, and parts of Canada and Washington, felt the earth’s convulsions over an astounding four continuous minutes–minutes, maybe, in which many folks had been contemplating the long, momentous death of one man on a cross. Those four minutes would prove momentous for the south-central Alaskan coast as well, and much was changed so that the shape of things here is now reckoned from them.

The consequences are still evident almost 50 years later, as we saw in several places we visited. Cordova’s Million Dollar Bridge was built in the early 1900s to haul copper on the railway and then converted in the 50s to a highway for visitors to the Childs and Miles glaciers, which flow into the Copper River from the Chugach mountains. It was destroyed in the upheaval and left broken for the next 40 years. Even now, sections of plank remain on the reconstructed portions, and the bridge is somewhat cockeyed where it was torn. Even the terminal face of Child’s glacier, visible from the bridge, is still largely masked by the earthen debris deposited on its southwestern flank.

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Orca Adventure Lodge, where we stayed in Cordova, was renovated from an old dorm for workers at the now-defunct Orca Cannery, which once harvested the abundant Razor Clams on the shore. The quake raised the seabed around Cordova six to eight feet, lifting clam beds out of the intertidal zone and crashing the clam industry there. Remnants of the old docks now stand isolated and rotting in the water, an old piece of machinery abandoned on an island of beams. Orcas, once frequent visitors, for the most part stopped entering Orca Inlet, now too shallow for their comfort.

Cordova dock

This sort of thing happened in many other nearby towns. Valdez, which we saw from our ferry back to Whittier, was originally four miles farther east, but it suffered enough damage to warrant relocation, and the native village of Chenega was destroyed entirely, a third of its population lost. A significant section of the Seward Highway on the Turnagain Arm, which we drove to visit Seward and Homer on the Kenai Peninsula, sunk below the high water mark in the tremor and had to be rebuilt in the following years. I don’t know the details of Seward’s damage beyond the expected wrecked buildings, but in Homer the popular Spit sank some eight feet, shrinking to a thin spur. The vegetation there died, leaving the gravel and sand surface that you see today.

Homer Spit

The Great Alaskan Earthquake killed 131 people, most from subsequent tsunamis, and destroyed several villages. It remains the second largest recorded temblor in history, and like all of the strongest ones it was a megathrust earthquake. These occur at plate boundaries, in this case the convergence of the Pacific and North American plates. What happens, essentially, is that the dense Pacific plate subducts beneath those surrounding it in the Ring of Fire. At the Alaskan coast, that means a slow build up of immense pressure as the Pacific compresses into Alaska some six centimeters a year. When that tension finally releases, the earth’s crust shifts and the denser Pacific plate crashes down below. Most of the time, these are subtle shifts, like an animal settling into sleep. But in 1964, the pent-up pressure was so huge that its release was catastrophic, a massive beast disturbed into paroxysmal wakefulness.

Childs Glacier

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About Nick

Nick sprang forth in the suburban-rural Midwest lands of Indiana and studied at Ball State University. Then he drove east to Boston. He spent his time there earning a master’s in Publishing and Writing from Emerson College and kicking it with the Harvard taekwondo team. Like so many before him, he then headed West seeking new fortunes and adventures. He worked as an editorial intern at Outside Magazine in Santa Fe, New Mexico, writing, fact checking, and interviewing strange folk. He's currently a freelance writer, martial artist, adventurer, and musician.

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