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Clayoquot Sound Geology
Clayoquot Sound Geology
Figure 1. Geologic map of Vancouver Island. Colors within cross-section view and overview map are consistent in describing geologic makeup of the region.
Figure 2. Graph indicating area of landslides that occurred, in m2 * 1000. Y-axis indicated the total number of landslides. Standard deviation, mean, and median of natural and logged areas in Clayoquot Sound have been included.
Citations
Guthrie, Richard. 2005. Geomorphology of Vancouver Island: Extended Legends to Nine Thematic Maps. https://doi.org/10.13140/RG.2.1.3411.8640.
Hyndman, R.D., C.J. Yorath, R.M. Clowes, and E.E. Davis1990 The Northern Cascadia Subduction Zone at Vancouver Island: Seismic Structure and Tectonic History. Canadian Journal of Earth Sciences 27: 313–329.
Jakob, Matthias. 2000. “The Impacts of Logging on Landslide Activity at Clayoquot Sound, British Columbia.” CATENA 38 (4): 279–300. https://doi.org/10.1016/S0341-8162(99)00078-8.
Massey, N.W.D., D.G. MacIntyre, and P.J. Desjardins. 2003a. Digital map of British Columbia: Tile Nm 10, Southwest British Columbia. B.C. Minist. Energy and Mines, Victoria, BC. Geofile 2003-3.
Massey, N.W.D., D.G. MacIntyre, and P.J. Desjardins. 2003b. Digital map of British Columbia: Tile Nm 9, Southwest British Columbia. B.C. Minist. Energy and Mines, Victoria, BC. Geofile 2003-4
“Nanaimo-Rock.” n.d. CGEN Archive. Accessed May 19, 2021. http://www.cgenarchive.org/nanaimo-rock.html.
Rollerson TP, Thomson B, Millard T. Post-Logging Terrain Stability. :13.
Rollerson T.P., Millard T.H., Collins D.A. (2005) Debris flows and debris avalanches in Clayoquot Sound. In: Debris-flow Hazards and Related Phenomena. Springer Praxis Books. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-27129-5_23
Wilson MC. Appendix A: Regional Geology, Geoarchaeology, and Artifact Lithologies from Benson Island, Barkley Sound, British Columbia. :14.
The geologic history of Vancouver’s coast is complex, with both glacial and fluvial processes had taken place. Part of the Insular Belt, Vancouver Island’s margin consists of a subduction zone, where the oceanic crust subducting underneath continental crust, with this molten rock supplying the Cascade Mountain chain (Hyndman et al. 1990). Vancouver’s bedrock geology consists of formations from the Cenozoic, Mesozoic, and Paleozoic eras (Guthrie 2005). It should be noted that the Cenozoic ranges from 66 My (million years) to present, Mesozoic from 66 My to 251 My, and Paleozoic from 251 My to 542 My (Massey et al. 2003a,b). Figure 1 gives an overall visualization of Vancouver Island. Mountains on the island play a key role in affecting the island’s climate, such as producing a rain shadow to the east (Nanaimo-Rock, CGEN Archive).
Landslides have been studied within Clayoquot Sound to understand how the effects of clear-cut foresting might have on their frequency of occurrence. Most logging had occurred along low elevations within Clayoquot Sound along the coast in valleys (Rollerson et al. 2005). This was up until the 1960s, where logging started to move to steeper areas, and therefore creating the foundations for greater occurrences of landslides, along with poor road-building being a contributing factor as well. Debris avalanches and debris flows are the most frequently occurring mass movements, most landslides occurring on southeastern slopes (Jakob 2000).
Certain formations such as the Sicker Group (Basalt, tuff, breccia, argillite): .80, Quatsino (Limestone, siltstone): .85, Island Plutonic Suite (Granodiorite, quartz diorite, quartz monzonite): .63, are all experiencing landslides at greater rates than the average occurrence, which is about .46 landslides per km2. Few landslides are associated with bedrock failures, and roots ability to penetrate bedrock influences slope stability. Open slope failures were shown to be the primary failure type.
Other variable such as slope at which the landslide occurred, how close it was to the coast of the island, the slope shape, and whether or not they occurred in a natural forest.
Climate Change in Clayoquot Sound
Climate Change in Clayoquot Sound
Figure 1: Stormwatching on the coast of Tofino
Figure 2: Algal bloom around a Millar Channel salmon farm
The entire world has been experiencing climate change, and the Clayoquot Sound is no exception. The west coast of Vancouver Island has seen a number of observed changes just over the last few decades. Summers have become warmer, now peaking above 30 oC. Additionally, summer rains have become much less common. Coastal lands and waters have been steadily increasing and are expected to continue to do so through the century. Nearby Kennedy Lake and Christie Lake water levels have remained consistently lower than their previous levels ("Clayoquot Monthly Climate Averages" 2011). Winters are now much more mild than they used to be in the Sound. Snow has become a less common phenomena as even more precipitation now comes down as rain. Lakes, ponds, and inlets are now entirely devoid of ice throughout the winter ("Clayoquot Monthly Climate Averages" 2011). Consequently, migratory animals are staying longer into the winter and coming back sooner as they take advantage of the milder weather in Clayoquot Sound. Climate change and other anthropogenic factors have put a lot of stress on the regional food web in the area, just as they do elsewhere. Clayoquot fish stocks as a whole are down significantly, especially the salmon species, which have served as a food source for First Nations peoples for thousands of years ("Clayoquot Monthly Climate Averages" 2011). Other species integral to the food web such as clams, muscles, shrimp, oysters, and seaweed also have dwindling numbers. All of the marine fauna in the area are smaller and generally less healthy. In addition to dwindling fish stocks, in the future this region is expected to experience increased water temperatures, algal blooms, as well as increased saltwater intrusion ("Clayoquot Monthly Climate Averages" 2011).
References:
Clayoquot Monthly Climate Averages. WorldWeatherOnline.com. 2021 Jun 4 [accessed 2021 Jun 4]. https://www.worldweatheronline.com/clayoquot-weather-averages/british-columbia/ca.aspx
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