Monday, March 18, 2013

Landslide Adventures and a Close Call

The last few days including the weekend have been a bit heavy on field work with some work a bit out of the way. Most of the work was geology hazard stuff. A sampling of some landslide adventures. 
Roads are long semi linear features to get from one point to another. As such unstable slopes are sometimes unavoidable.
Slide areas are expected on steep slopes, but in this case the steep slope is a fair bit away from the road. Regardless about 2/3 of the road has dropped several inches and has been patched multiple times. I traced the main fracture from the edge of the road approximately 150 feet across the clear cut harvest area - all on essentially flat ground. A secondary ground fracture happened to have opened right at the sign; hence, the sign was twisted sideways. If this slide progresses to a full collapse, the road fix is going to get more expensive than a bit of asphalt to smooth the dip.
The above home is for sale. It has been red tagged as the landslide complex on the site has expanded and reached the home's foundation. The sale fliers do note that the home can can not be occupied. It will need to be moved or left to its fate. The home was located 280 feet back from the top edge of the shoreline bluff slope. However, the entire upland between the home and the top edge of the bluff has begun to fail. Large stretches of this landslide reactivated in the past few years.
Note fractures in the former yard area and a few tilting trees on the slide area.
Sam found another slide's source when she sunk to her belly in what could be described as "baby diarrhea". Springs of very fluid mud on the slope were causing the slope above to drop and unfortunately a couple roads as well.

View up slope to scarp across road
The slide shown below shows the another road traversing across the upper headwall area of a slide. A new scarp can be seen just to the lower right of the orange sign in the distance on the right side of the picture. I would note that the road itself added some mass onto the slope. The relatively recent timber harvest likely has resulted in additional water onto the slide. And this winter has been on the wet side with this particular area having been impacted by well above average rain fall in the late fall.
My biggest excitement was exploring the stability of the slopes in a ravine where I documented a number of slides of various ages.
The lack of trees and sword ferns in the central part of the image and on the far left are from past shallow slides on the slope and the debris on the lower right is from a slide this past winter.

Recent shallow failures on the lower slope causing the slope above to become unstable
I recorded numerous slides within this deep and steep ravine. After a rough scramble back up the slope to the top I was chatting with someone about my ventures when a slope in the ravine slid taking several trees to the bottom of the ravine. Based on my notes and mapping, the slide took place at the spot pictured above. Yikes! I had very little interest in verifying if in fact it was the slope pictured above that failed. Creepy, nasty ravine.

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