Author: QMPGEOadmin

05-19-18 Melanie Kelman: Vancouver to Whistler, B.C. Geology

QMPGEOadmin

About the Talk

The Geology of Southwest British Columbia’s Sea to Sky Region

British Columbia’s Sea to Sky Highway (Highway 99, connecting Vancouver to Squamish, Whistler, and Pemberton) provides a journey through the geology of British Columbia’s Coast Mountains, where relief from valley floors to summits is commonly 1500-2000 m. The highway follows the steep fjord wall of Howe Sound past waterfalls, debris flow-prone gullies, rockfall hazards, glacial erosion features, and the Britannia Beach copper mine (operational until 1974), before arriving in Squamish. The town of Squamish sits at the head of Howe Sound and is located near the 700 m cliffs of the granitic monolith, the Stawamus Chief, as well as the dormant volcano, Mount Garibaldi, and a debris fan comprising mainly volcanic material from Mount Garibaldi, including material that was originally deposited supraglacially before being remobilized when the Cordilleran ice sheet disappeared. North of Squamish, the Sea to Sky Highway climbs from a floodplain and winds its way through the Cheakamus River canyon, with views of the mountains and glaciers of the Tantalus Range to the west. The vertical cliffs of the Barrier mark the site of a mid-nineteenth century landslide from an andesite lava flow that ponded against remnants of the Cordilleran ice sheet during the waning stages of the Fraser Glaciation. At Brandywine Falls, the Brandywine River cascades over a stack of basaltic lava flows and drops 70 m into a canyon. A series of lava flows of Cheakamus basalt next to the highway show evidence for eruption beneath or beside ice. In Whistler, the gondolas to the top of the ski slopes allow for broad views of the geology of the Coast Range, including the volcano, Mount Cayley, located 15 km west of Whistler (but not visible from lower elevations). North of Whistler, Nairn Falls, located 1.5 km from the highway, has numerous large potholes and other features eroded by water. The town of Pemberton lies about 60 km southeast of the volcano, Mount Meager, which in 2010 was the source of the largest historic landslide in Canada (about 49 million m3). Although Mount Meager occupies only 2.5% of the area of the Lillooet River watershed, it is the source of 25-75% of all the sediment deposited in the Lillooet River valley during the Holocene. Three prehistoric debris flows from Mount Meager, including one contemporaneous with its 2350 BP eruption, reached as far as currently inhabited areas of Pemberton. This eruption, the only known explosive Holocene eruption in Canada, left an ash layer that today can be traced as far as central Alberta, more than 500 km downwind.

Read about the Sea to Sky GeoTour…

About the Speaker

Melanie Kelman is a volcanologist with Natural Resources Canada (NRCan) in Vancouver. She first became interested in geology as a child, when her father, a hobby rock collector, took the family to quarries, gravelly lake shores, and mine dumps around western Canada and the United States. She completed a B.Sc. at the University of Saskatchewan in 1994, an M.Sc. at Oregon State University in 1998 (studying altered seafloor rocks from the Tonga trench in the southwest Pacific), and a Ph.D. at the University of British Columbia in 2005 (studying volcano – ice interaction at southwest BC’s Mount Cayley volcanic field). After brief stints working in the industry, drilling for metallurgical coal and then looking for gold in ancient volcanic rocks, Melanie started work with NRCan in October 2007 during the Nazko region volcanic seismic swarm (which did not lead to an eruption). She currently devotes her time to volcanic hazard research, volcano emergency planning, and the preparation of educational materials. If volcanic unrest were to occur again in Canada, she would play a major role in monitoring, hazard assessment, and eruption forecasting.

Melanie Kelman in the news…

Kamloops This Week 2017 Volcanoes in B.C…

CBC 2016 Dormant B.C. Volcano…

03-31-2018 Tom Badger: Landslide Hazards

QMPGEOadmin

About the talk

Geology, gravity, and growth: the risky business of landslide hazards in Washington

Landslide hazards abound in Washington State. They impact our shorelines and rivers, forests, infrastructure, homes, and livelihood; and on rare occasions, they result in loss of life. Tens to hundreds of millions of public dollars are spent annually in Washington State to mitigate for these impacts. Some of the better known hazard areas for frequent and/or large-volume landslides are associated with the glacial deposits of the Puget Lowland, the marine sedimentary rocks of the Olympic Peninsula and Willapa Hills, and the basalt-sedimentary interbed sequences of the Yakima Fold Belt.

Proactive response to a particular hazard is driven by the recognition of potential environmental and societal consequences and imminence (predictability) of occurrence. The latter factor can be difficult to characterize, recently exemplified by the Rattlesnake Ridge landslide near Yakima. More often, landslides unexpectedly happen and society responds reactively. Despite the human tragedies associated with these events, notable historical landslide events in Washington, such as the 1980 Mt. St. Helens eruption, the 1983 Lake Whatcom debris flows, the 1996-7 winter events, and the 2014 SR 530 (Oso) landslide, generated high-value societal benefits. These include the implementation of forest practice rules for timber harvest and road-building, professional licensure of geologists, risk-management programs for public and private infrastructure, streamlining of emergency management procedures, landslide hazard mapping, and scientific advancement.

About the Speaker

Tom Badger is a retired engineering geologist for the Washington State Department of Transportation (WSDOT). He shared thought provoking images including an example of the Rattlesnake Ridge Landslide south of Yakima and why predictions are challenging.

Tom Badger in the news:
Seattle Times Jan. 2018 Geologist warns Yakima area landslide could be worse than officials expect … “how hard it is to predict the behavior of a massive, unstable pile of rock and dirt,” said Tom Badger

Seattle Times Feb. 2010 about Naches slide

 

Crescent Lake Field Guide

QMPGEOadmin
Map from Washington Water Science Center – USGS

by James Aldrich Ph.D. – Sept. 2013

To read/print the whole Olympic Field Guide, click here…

Location Details

Lake Crescent Overlook – Roadcut in Crescent Formation, Tcb unit of Tabor and Cady (1978a). Flows of black pillow basalt striking approximately east-west and dipping steeply (~850) north; dense to highly vesicular; contains microphenocrysts of clinopyroxene [Fe, Mg, Ca, Na, SiO2, and Al] and calcic to soda plagioclase [(Ca, Na) (Al,Si) AlSi2O8]. A submarine flow at Crescent Lake, just below the contact with the overlying Aldwell Formation yielded an 40Ar/39Ar date of 52.9±4.6 Ma while the base of the submarine Crescent Formation flows on Hurricane Ridge Road yielded an 40Ar/39Ar date of 45.4±0.6 Ma. These two dates suggest the Crescent Formation, while mapped as a single unit between these two locations, had more than one eruptive center (Babcock et al., 1994).

There is disagreement among investigators as to whether the chemistry of the basalt justifies separating the formation into lower and upper members. Glassley (1974) and Muller (1980) maintain that the chemistry points to two members – a lower mid-ocean ridge basalt (MORB) and upper oceanic island basalt (OIB) member. Cady (1975) and Babcock et al, 1994) argue there is no clear difference in chemistry between the upper and lower members. More work needs to be done to resolve this issue.

Fundamental to the geology of the Olympic mountains is the basalt which makes up so much of them. This is rock created at mid ocean ridges which sea floor spreading brings to continental margins where subduction is occurring, part of the conveyor belt of earth surface crust with formation in the ocean and consumption beneath continents.

Basalt is also made in oceanic islands where hot spots are burning through the ocean floor to feed volcanoes like Hawaii. Subduction wedges basalt and deep ocean sediments into the continental margin and builds out the land mass over time using slices of the oceanic material as construction material.

Crescent Basalt: Flows of black pillow basalt striking approximately east-west and dipping steeply (~85°) north. Pillows show that the lava was extruded onto the seafloor where it chilled rapidly into a solidified mass. This basalt dates from 53 to 45 million years ago when it rose at a sea floor spreading center. Spreading carried it continentward, and subduction jammed it into the margin of North America.