Thursday, October 27, 2011

Goose Egg Hill, Hanford

This a post that I initially thought would take 5 minutes to write up. But the more I looked at this hill the more interesting it got. The post is based on the referenced geologic maps, but the land form itself and how it survived the Missolua floods is my own interpretation. I was not able to find any specific interpretation of the hill; hence, the interpretation is mostly my own but with reliance on a lot of great work by others in the area and my interpretation should be not be considered peer reviewed.

Approximately half way across the Hanford area on the northeast side of Highway 240 is a conical hill, Goose Egg Hill. Its conical profile is unusual in this area. The hill is a natural feature; although given its location within a weapons grade nuclear production reserve, one might speculate it is man made. The scale of the hill is difficult to discern as it is located in a landscape without scale. The hill is approximately 140 feet higher than the surrounding plain.

Goose Egg Hill, Hanford

Goose Egg Hill location (Google Maps)

The geology of the hill has been variously interpreted over the years. I have a colorful geologic map series (Rockwell, 1979) that indicates the hill is part of the Pasco Gravels. The Pasco Gravels were deposited by flood waters from the Missoula floods. A previous interpretation was the hill was a large mound of debris deposited by a grounded ice berg left behind by the floods. There are berg mounds in the area Bjornstad and Fetch (2002). Reidel and Fecht (1994) interpret the hill to be underlain by a pre Missoula flood gravel unit that underlies the oldest Missoula outburst floods with a correlated age of 1 to 3 million years old. Bjornstad and Fecht (2002) suggest that it may be a remnant of a dissected flood bar.

Given the conical shape, I prefer the the Reidel and Fecht (1994) interpretation that it is an older feature that predates the Missoula floods. This area was likely elevated prior to the flood as it is located along the inferred axis of an anticline (Reidel and Fecht, 1994). Hence, the area where the hill is located would represent uplifted fluvial deposits from an ancestral Columbia River or a tributary. Under this interpretation, the conical hill shape is an erosional remnant that is reminiscent of a similar hill above the Yakima River (pushtay-odd-hill-near-selah-washington).

One problem with the interpretation that Goose Egg Hill represents an older erosional surface is How did this feature survive the Missoula floods that inundated this area? An overview of the Hanford area and the flood water is provided by Bjornstad and Fecht (2002).

Hanford Area from Bjornstad and Fecht (2002)

Goose Egg Hill is located near the center of the map above as indicated by the letter (G). Initially the flood waters poured into the area via Sentinel Gap to the north and the Othello Channels to the east. Initially Goose Egg Hill would have been above the flood waters. The hill would not be inundated until the water backed up from the restriction at Wallula Gap just off the southeast corner of the map. Under this interpretation Goose Egg Hill was inundated with quiet water simply pooling into the short lived Lake Lewis formed by the constriction at Wallula Gap. There were still currents from the large volumes of water rushing into the lake and these currents created the huge gravel bars - Cold Creek Bar and Priest Rapids Bar located north of Goose Egg Hill. The hill was far enough away from the high currents that it was not eroded and far enough away that that is was also not buried by the bars.

Still water deposits of silt (Touchet Beds) likely covered many areas that were inundated where there was little current, but those silts were stripped away from many areas as currents developed again as the lake drained away. The above map indicates silts underlie the area southwest of Goose Egg Hill, and the flood silt deposits are also indicated on all of the geology maps of the area and are readily apparent along the highway in this area. It may be that Goose Egg Hill happened to be located at just the right spot where the currents were not strong enough to erode the hill but there was enough current to prevent the hill from being buried in silt and the hill was far enough downstream from the building Cold Creek Bar that it never got buried. As the lake drained current channels developed forming the Central Hanford Braidplain to the northeast of Goose Egg Hill. After the floods, the area has been further altered by winds moving sand deposits from the flood into dune fields that now cover much of the Central Hanford Braidplain.

The area around Goose Egg Hill holds another surprise. Take a gander (pun sort of intended) at the area around Goose Egg Hill and note the crack-like surface on the surrounding plain.

Goose Egg Hill and patterned ground (USGS)

The patterned ground is not very apparent except from the air as in the above satellite image. Note the scale. The pattern is the result of clastic dikes forming in the rapidly deposited flood sediments (Bjornstad and Fecht, 2002). As the mass of new sediment pressed down on previously deposited sediments the underlying sediments were compressed squeezing water out. The escaping water ruptured through the overlying sediments. The fractures are filled with sediment from the underlying material and are called clastic dikes. The soils along the clastic dikes at the surface have different porosity and water holding capacity and thus the clastic dikes are expressed by variation in plants that grow on the surface which is visible from the air or to a clever observer on the ground.

It would be great to take a walk about to the summit of Goose Egg Hill and examine the proposed hill theories as well as the clastic dikes on the ground surface. However, the hill is located in the United States Department of Energy Hanford Site.

Goose Egg Hill and trespass warning

The Hanford area geology has been an intensely studied due to the extensive areas of subsurface contamination as well as detailed investigations associated with a formerly proposed nuclear waste repository. Hence, the mapping in the area is very detailed and our understanding of many features in eastern Washington has a great deal to do with detailed studies associated with the nuclear facilities at the site.

Highway 240 cuts across the Hanford Area northwest of Richland. This highway was completed in the late 1960s and in the 1970s was an interesting road to drive. It was a through route across the United States Department of Energy Hanford Site. This large tract of land was set aside for the production of weapons grade nuclear fuel during World War II. The small town of Handford and the farming communities along the river were condemned and those that lived there had only a few weeks to move. They were only allowed back for a brief period to harvest the last year of farming crops (Dale Webber, personal communication, 2011).

The highway passes nowhere near the old town or the nuclear facilities. Only distant glimpses of the facilities can be seen. The road passes through the driest area of Washington State. The combination of the Cascade Range rain shadow, the low elevation as well as the high ridge of Rattlesnake Mountain lowers the average rainfall to 6 inches per year. It is also one of the hottest places in the state during the summer.

The highway is now essentially the boundary between the United States Department of Energy Hanford Site and the Hanford Reach National Monument. The initial Hanford site was large for the purpose of secrecy and security and much of the area became a large wilderness. For a time the area had a herd of wild horses and in more recent years elk have moved into the area to graze on the vast grass lands on a seasonal basis.

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