The Big One

Earthquake Park, Anchorage, Alaska

On this date in 1964, which happened to be Good Friday, the largest earthquake in US history struck Southcentral Alaska. With its epicenter in Prince William Sound and its magnitude measured as 8.6 or even higher on the Richter Scale, the Good Friday earthquake caused massive destruction throughout the region. The nearby town of Valdez was completely destroyed and later rebuilt on a different, less seismically vulnerable site. Other towns such as Seward and Whittier didn’t suffer that fate, but 13 of the 70 residents of Whittier died in the quake and the following tsunami, and port facilities both there and in Seward suffered so much damage that they have never fully recovered their economic importance.

Anchorage, which was a bit further away, suffered somewhat less, although it was still hit hard. Indeed, its port managed to stay open in the aftermath of the quake and tsunami, which was one of the factors making Anchorage become the main economic center for the region and the whole state in the following years. This is not to say that the earthquake wasn’t a major disaster for Anchorage as well, however. The city was built on sediments that turned out to be pretty vulnerable to shifting when hit with an impact of that scale, and parts of the downtown were literally torn apart. An upscale residential area known as Turnagain Heights suffered a landslide so devastating that the city, rather than attempt to rebuild, designated it as a park. It is now aptly named Earthquake Park, and while there isn’t much obvious evidence of the effects of the earthquake anymore, there are interpretive signs that tell the story quite effectively.

Sign Describing Turnagain Heights Landslide, Earthquake Park

Earthquakes are a fact of life in Alaska, which just north of the area where the Pacific Plate slides under the North American Plate (known as the Aleutian Trench). This movement is continual, but it only occasionally occurs in the form of massive slips of the sort that cause earthquakes on the scale of the one in 1964. The more usual effect is to warp and compress the land of Southcentral Alaska. This warping, along with other factors such as glaciation, leads to complicated changes in sea level over time, changes which can vary substantially in areas only a few miles apart.

And that, in turn, greatly complicates study of the archaeological record of Alaska. Rising sea level typically destroys archaeological sites (although in certain very specific circumstances it may instead preserve them in excellent condition), and changes in sea level over time may make sites from a given time period difficult to locate even if they haven’t been submerged. Furthermore, cultures of coastal Alaska have generally been oriented toward the sea, with settlements typically located fairly close to wherever the coastline was at the time. This means that sea-level fluctuations have even more profound impacts on understanding the archaeological record here than they might in some other areas.

Interpretive Signs at Earthquake Park

These factors are illustrated dramatically in a 1996 article by Aron Crowell and Daniel Mann reporting on research in Kenai Fjords and Katmai National Parks attempting to carefully document sea-level changes and their effects on the archaeological record. These two parks are not very far from each other, being about 200 miles apart and both located on the coast of the Gulf of Alaska, but their geological and cultural histories differ dramatically. Kenai Fjords, as its name implies, is dominated by coastal fjords created when rising sea level inundated glacial valleys. Its archaeological record is sparse and limited to the past few centuries.

Katmai, on the other hand, has a relatively stable coastline and an enormously rich and well-documented archaeological record dating back several thousand years. Much of what is known about the archaeology of southwestern Alaska is based on long-term research in various parts of Katmai by Don Dumond of the University of Oregon from the 1950s through the 1980s, and there has been considerable additional research since then. The cultural sequence in this area closely parallels that of the nearby Kodiak Archipelago, which was one of the most densely populated parts of Alaska when the Russians arrived in the eighteenth century. The Kenai Fjords area, on the other hand, had a much lower density at this time, as did Prince William Sound further east, with which it has many similarities. This lower density has been plausibly attributed to lower resource productivity in these areas, but Crowell and Mann point out that the extremely low density of prehistoric archaeological sites in Kenai Fjords is perhaps also due to geological processes and seal level change.

Welcome Sign, Earthquake Park

To investigate the differences between the two parks, Crowell and Mann intensively investigated certain parts of each, with intriguing results. One of the areas investigated in Kenai Fjords was a narrow sand spit with a series of beach ridges containing a total of four archaeological sites (most dating to the eighteenth and nineteenth centuries and the earliest about 500 years old) and a small tidal pond surrounded by trees killed when the 1964 earthquake caused the land to drop about one meter, exposing their roots to the seawater that permeates the sandy soil. This same seawater also fills the pond, so the sediments in and around it could be interpreted as a record of changes in relative sea level over time. Digging down in search of radiocarbon-datable material, the archaeologists found a series of buried tree stumps 1.8 meters below the present surface that seemed to have been killed in a sudden cataclysm surprisingly similar to what happened in 1964. Six radiocarbon samples taken from the bark of these stumps gave dates that were statistically identical and averaged out to about AD 1170.

This strongly suggests that there was a major earthquake at least as strong as the Good Friday one in or around 1170. This is consistent with evidence from several other parts of the region, where other studies have found less precise evidence for major geological changes around this time. The implication for the issue of archaeological site preservation is that any coastal sites in this area predating 1170 would have been destroyed by the earthquake. Since the geomorphology of Kenai Fjords means that the only usable settlement locations here are on low coastal sand spits like this one, this earthquake probably completely destroyed the previous archaeological record. This would explain why there are so few sites in the park, and why they basically all date to the late prehistoric period or later. The relatively low productivity and other drawbacks of the area may well have limited population earlier as well, but with the earthquake having destroyed any evidence of what was going on previously there’s no way to know for sure.

Sign Describing the Good Friday Earthquake, Earthquake Park

Katmai was a different story, however. Crowell and Mann discovered 22 new sites there in the course of this project (as compared to 16 sites total in Kenai Fjords documented by this and other projects), suggesting that further survey along the coast will likely reveal even more as yet unknown sites in this very productive area. Interestingly, many of the sites they found were located away from the present coastline, often in uplifted areas that may have been coastal at times of higher sea level than at present. Radiocarbon dates from these sites and from peats in the intertidal zone allowed Crowell and Mann to reconstruct a tentative sea level curve for much of the past several thousand years, with the main conclusion being that sea level has been pretty consistent over the past 4000 years, with a slight rise sometime in the past couple hundred years, possibly as a result of subsidence of land in the 1964 earthquake. (Crowell and Mann don’t discuss the possibility that global sea level rise as a result of climate change may be another explanation for this, but it strikes me as plausible.) In any case, whatever the source of this slight recent rise in sea level, it had few apparent effects on archaeological site preservation beyond contributing to the exceptional preservation of one waterlogged site. The subsidence from the 1964 earthquake was very slight in this area, and this appears to have been true for the 1170 one as well. The rich archaeological record of the Katmai coast, then, appears to be in part a function of the relative stability of sea level in this area over thousands of years, in striking contrast to areas just a few hundred miles away.

The archaeological record is always incomplete, and any conclusions drawn from it have to be tempered by knowledge of that incompleteness. As this paper demonstrates very effectively, however, the factors determining just how much of the past is left for us to study vary a lot, especially in places like Alaska where the forces of the earth are exceptionally active. The modern population of Alaska learned just how active those forces can be in 1964, and it stands to reason that the ancient population learned the same lesson in 1170.

"Living with Earthquakes" Sign, Earthquake Park

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