Shallow surface landslides have been a bother to the rail lines between Everett and Seattle almost every winter. This particular slide took place in south Everett. A Longshoreman, John Hill, noted the slight soil movement as well as wet areas with flowing water and aimed his camera. Great work.
The rail line in this area traverses along the base of a former steep shoreline bluff. Fill placed at the base of the bluff created the rail line route. In a way the rail road acts line the former shore. Every time there is a slide, the soil is removed and hence the slope remains over steep without a buttress of landslide debris at the base of the slope. The rail workers that clear the slides from the tracks are acting like waves. What is not clear is whether the slope was cut into to make room for additional rail lines. I suspect in places it may have been.
The bluff slopes along this particular area are on the order of 100 feet high. They get even higher further south and there are some very large landslide complexes near Edmonds and Mukilteo as well as some very steep high bluff areas near Woodway. At this particular location the bluff is underlain by pre Vashon transitional beds. These sediments were deposited prior to the last glacial period (Vashon) and transition upward into melt water deposits as the glacial ice advanced into Puget Sound approximately 17,000 years ago. The lower, older sediment, is alluvial and non glacial and then transitions upwards into the glacial related sediments. Because these sediments were deposited before the ice advanced over the area these soils have been highly compacted by the mass of glacial ice.
The siltier units cause areas of soil saturation and with steady rainy days of late we have plenty of saturated soils. I would describe the slide as a small surficial slide. Some geologist use the term skin slide. Even a relatively small landslide has plenty of momentum to easily knock rail cars off the tracks.
Passenger rail is prohibited from passing through this area for at least 48 hours after a slide and this reach of rail has been closed for passenger service for something like a week or more as there have been numerous slides. Clearly there was a risk of slope failure that I am sure BNSF was well aware of. I do not know if BNSF has any clear policy as to movement of freight through areas that are obviously about to fail and what the cost of damages from numerous mangled rail cars and shipments would cost BNSF versus the cost of having the freight sit.
The bluff slopes along this particular area are on the order of 100 feet high. They get even higher further south and there are some very large landslide complexes near Edmonds and Mukilteo as well as some very steep high bluff areas near Woodway. At this particular location the bluff is underlain by pre Vashon transitional beds. These sediments were deposited prior to the last glacial period (Vashon) and transition upward into melt water deposits as the glacial ice advanced into Puget Sound approximately 17,000 years ago. The lower, older sediment, is alluvial and non glacial and then transitions upwards into the glacial related sediments. Because these sediments were deposited before the ice advanced over the area these soils have been highly compacted by the mass of glacial ice.
The siltier units cause areas of soil saturation and with steady rainy days of late we have plenty of saturated soils. I would describe the slide as a small surficial slide. Some geologist use the term skin slide. Even a relatively small landslide has plenty of momentum to easily knock rail cars off the tracks.
Passenger rail is prohibited from passing through this area for at least 48 hours after a slide and this reach of rail has been closed for passenger service for something like a week or more as there have been numerous slides. Clearly there was a risk of slope failure that I am sure BNSF was well aware of. I do not know if BNSF has any clear policy as to movement of freight through areas that are obviously about to fail and what the cost of damages from numerous mangled rail cars and shipments would cost BNSF versus the cost of having the freight sit.
6 comments:
Dan, is this the route the coal trains plan to take?
What's the fixation with the coal trains? You do realize that coal is nothing but carbon deposits dug out of the ground, right? You'd think we were talking about plutonium.
Dave: Yes it is the same route at least on the way. Some of the empty coal trains return via Stevens Pass and leave this line just to the north of the landslide area.
jvon: You seem to be bringing a conversation from somewhere else. The post never mentioned coal. Given the number of coal trains that may pass this spot, interest in the route are understandable.
What is the plan for those spots along the Chuckanut Highway where the entire mountain side looks like it might slide off into the Sound? I think I've read in one of Don Easterbrook's geological histories that part of the Chuckanut Formation lies on a rather slippery bed of (coal?) and sometimes slides right off the mountain onto the highway. Is a massive movement of the Chuckanut Formation a possibility? If it happened would it take out the rail line below? Certainly, this doesn't look so far fetched when you drive down Chuckanut Highway. At points, it looks like the entire highway is about to tip right on top of you...
Ryan: Lots of rock fall on a portion of the highway due to joint intersections with bedding combined with the road cut. I do not know the conditions of the rail cut slope below that section of highway as I have not been down there. I do not recall any reported problems or closures of the rail line on that section of track. My impression is that on that section slope cuts are minimal.
The rail workers that clear the slides from the tracks are acting like waves. Loading Arm
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