Vajont Dam Landslide Remote Tour Including Street View of Geologic Investigation

The 1963 landslide at Vajont in northern Italy was an horrific event that killed 2,500 people. The slide involved the a very large collapse of a bedrock mountainside into a new reservoir that was filling behind a dam constructed in a narrow canyon. The slide displaced a huge part of the lake over the dam with many of the fatalities downstream of the dam as well as hundreds of meters up the slope across from the slide. The slide speed has been estimated at over 60 miles per hour based on the wave of water generated as the slide displaced the lake.

Dave Petley has put up several posts on the slide and provides an excellent description of the slide and the events leading up to the slide including engineering efforts to monitor and control the slope failure before the rapid collapse of the slope: the-vajont-landslide-of-1963. The post also includes a list of references of papers published on the slide

As a fair bit of my work is assessing geologic hazards I took a remote tour of the slide via Google earth. The tour included a surprise street view scene of active geologic investigation of the landslide.

Outline of landslide area (south is towards the top)

Note Casso at the bottom of the image. I am not sure if the town is in the same spot as in 1963, but the 1963 town was destroyed by the wave of water that surged up the slope. Towns in the valley to the west (north is towards the bottom of the image) were all destroyed.

Street view of top of dam with slide in the background

Note the bedding surface orientation of limestone units

The dam survived the slide. Hydro power is now generated via a tunnel to the lake that has formed behind the landslide.

View of slide from near Casso 

The road in the image is traversing up the toe of the landslide

View of slide from the upper toe of the slide from the road shown in the image above

Road on the landslide with GPS surveyor

Seismic line stations along road 

The seismic survey consists of a string of recorders that will pick up shock waves traveling through the subsurface. The waves travel at different speeds through different materials, are reflected or refracted off of sharp contrasts. Hence, the recordings can be used to map the subsurface.

Andrea Wolter summarizes a recent paper on Vajont on the Landslide Blog: the-vajont-slide.

The Vajont slide took place during the era of large dam building throughout the world. As such, the failure has generated much interest in engineering geologists and geotechnical engineers. The topic of new large dam projects is raised more frequently as a means to address climate change impacts. Vajont is a lesson that needs to be well understood before projects are undertaken - a lot can go wrong.

Tsunami and Straits - the BC Version

The following images are from AECOM (2013) modeling of a Cascadia earthquake event generated tsunami into the Strait of Juan de Fuca. AECOM generated the model using a tsunami model developed by Cheung and others (2011) and utilizing digital elevations and bathymetry across both U.S. and Canadian waters (not so easy given the differences in how the two countries handle this data). The purpose of AECOM's work was to provide tsunami inundation, drawdown and velocity to the BC provincial capital area of Victoria on the southeast end of Vancouver Island. The work provides some localized information for areas of Washington State as well.

Maximum water level estimates

The maximum water level increase has some interesting aspects. Areas along the shore of the Strait at several places water level increases on the order of 4 meters. Just past the southwest tip of Vancouver Island, the maximum water level drops off as the inlet widens into Haro Strait. But past that dampening effect are a few hot spots. One is the build up of water height as the water surges into Rosario Strait and becomes constricted within Rosario Strait, Guemes Channel and Bellingham Channel. The result suggests that low areas along the east side of Lopez Island, southeast side of Decatur Island, South side of Cyprus Island and west shore of Guemes Island and north shore of Fidalgo Island will see much higher water levels from the event than other areas even a short distance away.

Two other red areas of high water that stand out are Port Discovery and Port Townsend, the two bays on the southeast of the image above. Both these bays have deep entrances and then become narrower towards the head of the bays and thus the water levels become enhanced as the water surge from the tsunami enters and floods into the bays. Indeed the head of Port Discovery has been investigated for tsunami deposits and several deposits have been documented (Williams, Hutchinson and Nelson, 2005).

One caution with this is how the elevated water will behave as it comes on shore and across tidal areas would require a significant more detailed analyses. Hence, a 4 meter rise in the strait may translate to a less or more inundation. Part of the AECOM's effort was to look in more detail at areas within the inlets of the Victoria area.  

Drawdown estimates 

The other tsunami impact is how low the water will go as the water is pulled out. The pattern of large drawdown areas is somewhat similar to the maximum water level areas but with a few shifts. The drawdown of water out of harbor areas plays havoc with ports as docks collapse and boats end up grounded and then the water surges into the harbor.

Qwuloolt Estuary Visit

I had a little time between a job in Marysville and one in Everett so I took a little detour and visited the Qwuloolt Estuary. The estuary is a recent project that is part of a larger project of estuary restoration on the lowermost end of the Snohomish River near Everett and Marysville. The project involved reconnecting the lower flood plains to the river and tidal influences by removing levees along the river. I worked on a very very tiny piece of the project last summer. An overview of the project can be seen HERE. The project also has a web page:http://www.qwuloolt.org/.

The estuary with Everett in the distance 

Estuary with Olympic Range

Estuary with Marysville business park across the water

Raised berms within the estuary to provide mixed habitat as well as reduce wave energy when the estuary is fully flooded

View of north end of estuary and Allen Creek and new levee protecting business park

Much of the lower end of the Snohomish River had been poorly drained farm land. There remains industrial land around Everett and Marysville, waste water treatment lagoons and a huge capped landfill.

The restoration work on other parts of the estuary has greatly altered the landscape along Interstate 5. But the expanse of work is much greater than what can be seen along the freeway. I accessed some views along a trail that is located between a neighborhood and the new estuary on the east side of the estuary. Overtime the project will bring about significant wildlife population changes including hunting and fishing opportunities.

   

West of Day Lake, Orcas Island

The east portion of Orcas Island is mountainous. The summit of the island is Mount Constitution at 2,409 feet. Relative to the other mountain areas in Washington it is not high, but the slope out of the sea water is abrupt and steep. East Sound the embayment on the east side of the island could easily be call a fiord.  The mountainous upland area has numerous mountain lakes both within Moran State Park and outside the park.  

Topographic map of the east portion of Orcas Island

Day Lake is on the north 

Just west of Day Lake is a small forested lake that clearly has expanded as part of the lake is full of dead trees. Day Lake Road passes by the east side of the lake. 

Day Lake on the right and the unnamed lake in the images above is on the left

(USGS, 2013)

1941 image of Day Lake 

A forest opening but no lake is apparent to the west

The lakes on the east of Orcas are almost all contained within bedrock basins that would have been partially eroded when the island was over ridden by glacial ice. The 1941 image suggests that the lake west of Day Lake did not exist but was a wetland area with few trees. Post 1941 rural development has taken place with scattered homes and gravel roads. Day Lake Road crosses the low area between the lakes and acts as a bit of a small dam across the drainage and hence the lake and the dead stand of trees in the water.

Day Lake Road on the northeast side of Orcas

A drive on Day Lake Road is a mountain road experience as the road descends the very steep northeast slope of Orcas from the lake to Raccoon Point Road. Great views across Rosario Strait to the BC Coast Range, but alas this last trip was a bit foggy just before a sleet storm rolled over the area. The road traverses a slope that is 1,300 feet high with a stead 45 degree or steeper slope all the way to the shoreline.  

An Unstable Day

I visit a lot of steep potentially unstable slopes for my work. Yesterday was a day of seeing very recent landslides and one in action.  

 

When I arrived at my first site, I noted a couple of city workers down the street from my location. A couple of boulders had come loose and landed on the city street below.   

 

 

After a late afternoon site visit to another site, I ended the day taking a hike along a shore reach I had not previously visited on Whidbey Island. I heard some deep thumping noises that sounded like artillery. While Whidbey Island is known for loud noise ("the sound of freedom" from the jets at the naval airbase), this was not a sound I had heard before.

 

It got louder as I headed north and then I saw the source: 

 

 

The large cracked block dropped off the bluff face when I was about 200 meters away. The bluff was acting like a glacial ice front in the sea, periodically calving off blocks of soil. This reach of bluff is all very compact glacial drift from the last glacial period - a rather thick section of till. As such the blocks are very cohesive and hard - almost like concrete.

However, the till does weather and becomes soft with water. When I walked over the toe of the area of collapsed blocks of till I encountered very fluid mud.

The source of water and the calving process were fairly evident on this wet day. Water has been flowing behind the dialation cracks on the till bluff face. Not a surprise given the amount of rain.

 

 

On my way back I took a picture in the dim light of a hanging bit of till on the bluff face.

 

 

 A minute later the slab had peeled off the bluff.

Alas I was not patient (it was late and raining hard) enough to keep the camera ready or quick enough to capture the event with the camera. I will simply say it was a cool thing to witness the slab rotate and fall off the bluff face.

Pre Clean Water Act 1956 Port Townsend Bay

Port Townsend Bay 1956 (USGS)

Indian Island is on lower right with weapons storage bunkers

I had a bit of office time today after a long field stint with more field on the way, hence the low posting.

I needed to do some aerial photo review before my next field run and came across this pre Clean Water Act and Clean Air Act image of the paper mill in south Port Townsend. Typical of the era, the mill formerly put out a remarkable plume into the bay that would not be tolerated today.     

Puyallup Reservation Map

Most road maps will show Indian reservations via a color shading on the map. That is the case for many of the Indian reservations in Washington State. The Yakama Reservation and Colville Reservations are easy to spot as they cover large areas. The reservations in western Washington are smaller and some are very small, but the ones large enough usually do get shaded in. Such is the case with the Lummi Reservation in Whatcom County.

The Puyallup Reservation is large enough to shade, but is typically left off maps.

Puyallup Reservation marked in red (Map USGS)

Puyallup Reservation aerial (USGS)

Close up of USGS Topo showing reservation boundary

The vast majority of the Puyallup Reservation is owned by non Indians. The buying up of the Reservation took place in the late 1800s via the Reservation being allotted into parcels to individual tribal members. Those members then lost their land through a series of illegal lease agreements that were converted to sales with the approval of Washington State with misleading reports to the U.S Congress. However, the Reservation boundaries remained in tact and are still recognized and has driven and continues to drive policy and land use in a very heavily urbanized landscape. 

The Spokane Sparrow

A bit pressed on time with other duties - but this was a fun find from inside the wall of an old cabin, a January 29, 1967 Seattle Times Sports Page:

In a different era Gerry Lindgren was an eastern Washington legend, and for those with memories that go back far enough he still is. Simply put he was the greatest long distance runner in Washington State history. His high school times were jaw dropping and he ran in the 1964 Olympics, the same year he graduated from Rodgers High School in Spokane. Part of his legend was how much he ran and how he raced. He inadvertently added to his legend when he disappeared in 1980 to parts unknown for several years.

This is a race I remember: a match in 1969 with Liquori, Shorter, Prefontaine and Lindgren:  http://www.historicfilms.com/search/?type=all&q=tele-1236#p1t24800i0o3393. This match between Prefontaine and Lindgren was a match between Oregon's greatest runner and Washington's greatest runner, and a match between two runners who ran extremely aggressive early paces.

Me and my running mates talked a lot about Lindgren and Prefontaine as well as Shorter, Liquori, Mills and Ryan. At one time or another Lindgren beat them all. As a young runner I studied how these guys ran. I never came close to their achievements. I had the wonderful experience of being in a race with Shorter. Physically it was a huge stress for me to stay on his pace; then he went into a whole other gear that I could never imagine being able to do - I was rapidly left far behind. 

Possible Glacier Peak Tephra West of Puget Sound

I was recently traversing a bluff to assess geologic risk above the shores of Discovery Bay on the northeast side of the Olympic Peninsula. The bluff geology includes a glacial recessional drift unit capping the top of the bluff. Below that is a recessional outwash sand and gravel unit. Further down slope are much older non glacial sediments (Olympic) and a glacial drift unit from two ice ages ago (Possession). 

The story on the upper bluff is a bit complicated as the units were likely deposited when the Puget ice lobe was retreating. The site appears to be located where the glacier lake that had been located in what is now Puget Sound drained when the ice retreated enough to unblock the lake. Sea levels were tricky at this time period. The ice age was coming to an end but there was still enough global ice such that sea levels were much lower than today; however, on a local level the mass of glacial ice had isostatically lowered the local land surface and hence the local sea level relative to today was substantially higher. All in all a location with lots to contemplate while thinking about slope stability and route finding on steep slopes.

Silty clay at bluff top with sand and gravel below.

I noted some white material within the sand and gravel that obligated me to take a closer look. I am ever hopeful of finding a mammoth fossil. Instead it was cluster of white pebbles within the coasre sand.
 

I pulled some of the pebbles out and found that they were pebbles of tephra. Tephra is very fine volcanic ash. Some how an ash deposit was eroded and shaped into pebbles by flowing water and deposited on the northeast Olympic Peninsula (The site is on the Quimper Peninsula which is attached to the larger Olympic).

The pebbles of tephra pose an interesting puzzle. How did tephra get all the way across the Puget lowland from a volcano in the Cascade Range? Based on the location and estimated age of the glacial deposits as very late most recent ice age outwash, I suspect this tephra may be from a large eruption from a Glacier Peak from 13,100 years ago. Tephras have distinct chemical signatures and as such this tephra could lend an additional age control to the units where it is located.  

Revetmant and Marie Dorian

Joseph Rose notes that Marie Dorion matches well with the recent movie Revenant (Oregon's Revenant). I have posted about Dorion previously (marie-dorion-one-very-tough-woman) - one of my favorite posts and while I post a lot of random stuff it remains one of my better posts. I remain fascinated with her story and the context of the story and her life in the Oregon Country.

The Cost of Living in the Mountains: The Swiss Experience

Doing a bit of work related research and reading and came across this perspective regarding communities in mountain settings and slope issues:

Hazards due to slope instabilities affect about 6% of the Swiss territory. The estimated annual cost for protection against landslides amounts to CHF 2.9 billion (Note the Swiss Franc is nearly at par with the U.S. dollar), which is about 0.6% of the gross domestic product or equivalent to CHF 400 per inhabitant. In 1991, new measures have been adopted to prevent and mitigate natural disasters. According to the federal recommendations, regional authorities (Cantons) are required to establish hazard maps to be incorporated in regional master plans and local development plans. ((Stozzi, Amrosi and Raetzo, 2013)

The cost of roughly $400 per inhabitant for living in the mountains and in areas of landslide risks suggests that if a state (say Washington) wants to keep geology hazard mitigation costs down it might be a good policy to consider limiting development in hazardous areas. Of course living in mountain settings does have a lot of appeal so maybe it is worth it.