An Almost-Petrified Forest
A letter received at the Geophysical Institute from Mr. Julius Sesky of Chitina had the notation "unexplained meteoritic(?) site" written at the top. As supervisor of the Poker Flat Research Rocket Range, the letter ended up in my hands, and its contents justified a telephone call to Mr. Sesky for more details.
Sesky told of a mysterious sand-filled depression near Chitina which measures some 200 by 400 feet across and has devastated trees with shattered and missing tops standing in it. The scene was reminiscent, he said, of pictures he had seen of the unexplained Tunguska area of Siberia where a meteorite or comet is thought to have impacted in 1908.
This was enough to pique anyone's curiosity, and for the next few days I checked with other members of the faculty and staff at the University to get their opinions on what the phenomenon might represent.
Then, one bright Fairbanks morning, my son Kris and I loaded an array of sampling and surveying equipment into the van and drove to Chitina. We found Mr. Sesky having coffee in a local restaurant, and he enthusiastically offered to take us to the site that same evening.
The infamous Copper River wind blasted us with sand as we walked along the river bluff to a point where it was cut open to a depth of about 50 feet by the southern end of the trench we had come to inspect. The first impression that one gets on viewing the scene is that the dead trees protruding from the sand in the trench had been devastated by a gigantic "brush hog" machine that had shorn them off about fifteen feet from the surface. On closer examination, slumping chunks of ground indicated to us that underlying permafrost might have somehow played a role in creating the depression, but it was getting late and we returned to our camp with the initial impression of the site fresh in our minds.
The next morning found us puzzling over the mystery of the trees. It appears that a curious cycle has developed in this isolated site. First, the river encroaches, allowing the surfaces layers of permafrost to melt, freeing the sand. The Copper River winds then pick up grit, dropping it under the effects of the local topography to form a dune on the western edge of the trench. The dune grows to its present 20-foot height and buries the lower parts of the trees. The sand-smothered trees die and the wind shatters their tops and blows them off. The prevailing winds then scoop the sand out from around the dead trees in the trench and progressively build the dune further to the west, where it envelops and slowly kills still more trees. When the sand blows away from around the dead trees, it exposes ground that now lacks insulating mats of vegetation, allowing the underlying permafrost to continue melting, with the result that the dead trees are now protruding from a deepening trench.
Areas in various stages of all the above steps can be identified at the site. At the southern and deepest end of the trench, which opens on the valley, there is only sand, dead fallen trees, and tree fragments. Midway along the trench, at the next higher level, the trees are broken off partway up. At the upper end, most of the trees are covered with sand and their tops are lying nearby.
Thus, a scenario such as that suggested above would account for most of what is found at the site today. Although variations on the major theme may have occurred, the suggested sequence of events would explain much of the continuing process.
We welcome ideas from scientists and laymen alike on what might be occurring in this uniquely Alaskan curiosity, and we extend our thanks to Mr. Julius Sesky for bringing it to our attention.
