Sunday, January 1, 2012

Some More Whitebluffs Landslides

Previous posts showed the large landslide caused by wetland creation at the north end of the Whitebluffs of the Hanford Reach National Monument huge-landslide-at-whitebluffs and slides at the south end of the Whitebluffs downstream of the Reach end-of-road-at-ringold-landslides.

There are other huge landslide areas. There is another large slide associated with irrigation water. This slide is located below a natural drainage area that receives run off from irrigation water. The water then flows via the subsurface to the face of the bluffs causing slope stability troubles. This slide is very similar to the northern slide as described in the previous post with a broad area of lumpy topography between the river the headwall scarps where the failure took place. And like the northern slide it too is lined along the top of the bluff with sand dunes. 

Large slide viewed from the south with gray sand dunes along bluff top
Saddle Mountains are in the background and Columbia River is on the left.

The water source for this slide can not be simply turned off like the north slide where the canal feeding the wetlands was simply no longer used. This drainage is at least partially natural, but now with significantly more water passing through due to irrigation from the Columbia Basin project. The water route follows one of the routes of the Missoul Flood. This problem has been partially addressed by directing water into a ditch and routing the water to a break on the bluff slope to the north.

Blue lines denote Missoula Flood water routes

Canal has been dug to route water to a valley between bluffs

Besides the more recent landslide activity, a very large landslide complex is located along the central area of the bluffs. This slide complex is no longer active, but is larger than either of the slides to the north. This slide complex is massive in scale with very large back rotated blocks that form sets of ridges parallel to the river and the top of the bluff.

North end of slide complex
View is from the bluff top looking down onto the north end of the slide
The ridge between the river and the bluff is a large back rotated slide block

Large rotated blocks between bluff summit and river

View towards the south with multiple back rotated slide blocks forming ridges between the river and the bluff top. The slide complex continues beyond what can be viewed from a single spot

The gravel road on this eastern portion of the monument comes to and end at the top of this slide complex. The road does continue down to the river but has been gated. Alas I was getting short on light so that hike will have to wait another day.

Two maps below might help route finding. This is an area that has undergone a bit of change so may of the roads besides the main route really don't go anywhere or end at gates. I am not sure of all the history of this area. Some roads were for hunting access which is more limited now that the area has become a National Monument. Some of the roads may also been used to access gun emplacements to ward of attacks on Hanford.

One thing I have not mentioned - this reach, the Hanford Reach is in reference to the river. Besides the bluffs and landslides, this area has been protected as federal land since World War II. Interesting that nuclear weapons production along with the Yakima Firing Range would save the largest block of intact scrub steppe in the Washington State. The Hanford Reach also is the only non dammed part of the Columbia River in Washington State above Bonneville Dam. The river along this reach is not entirely free flowing as dams upstream control flows, but Hanford Reach has river braids and complex channels and velocity. The healthiest and nearly only main river stem salmon spawning grounds are along this reach of the river.

1 comment:

Sandra Bowman said...

It is a shame to be losing the land behind the White Bluffs to landslides. On a tour of the area before the National Monument was established, I was told the cost per acre of that land was very high because it was such good agricultural property.
Also a person can see the salmon redds from a plane at the right time of year.