Friday, October 9, 2015

Basalt Landslides south of Wenatchee

Last Spring I was south of Wenatchee along the Columbia River and got a good view of several very large landslides that had come off the high basalt slopes above the valley.

Large slide complex off of Badger Mountain
The terrace in the left foreground is the Pangborn Bar from an ice-age flood
The vertical relief of the slide is almost 2,000 feet

Slide and rock fall off of Jumpoff Ridge southwest of the Columbia

Another slide off of Jumpoff Ridge



The two Jumpoff Ridge slides viewed from a bit further away
The vertical relief of these slides is a bit shy of 2,000 feet 

The area below Jumpoff Ridge is a huge landslide complex of sliding blocks. The slide complex is too big to take in and is the largest in Washington State. The slide complex extends all the way to the top of the high ridge. 

The headwall of the slide area up on the snowy slopes 

Waitt (1982, Wenatchee Geology Map) describes the slide complex and noted that it predates the ice-age flood deposits. But he also described large translational intact blocks on the upper slide area suggesting post ice age slope movement.  
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4 comments:

  1. AnonymousOctober 11, 2015 at 8:17 AM

    I was thru there the other year and didn't recognize these. Thanks for the elucidation.
    What I did recognize from childhood was a big funny-looking rock sticking up out of the Columbia in East Wenatchee, looking somewhat like an iron set on its heel. Someone said that was the result of a slide also. What do you know about it? Got pix?

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  2. Dan McShaneOctober 16, 2015 at 8:10 AM

    I am not familiar with that rock you mention. Will look for it next time I am in Wenatchee or East Wenatchee.

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  3. susanOctober 17, 2015 at 9:51 AM

    I thought the large basaltic rocks in the river in that area are from the Malaga Slide. See here, too. Might be something in this, also.

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  4. Dan McShaneOctober 17, 2015 at 9:34 PM

    Susan: I suspect you are right the rock is part of the Malaga Slide. I did a look at Google earth and could not see any large rocks in the river upstream of the slide area.

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