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| Swirling river undercutting rock |
November 10, 2011 - This field trip was undertaken to examine the workings of the river, in all it's aspects, i.e. to identify various formations, surficial materials, fluvial features, and describe current and anticipated human impacts on river flow, vegetation, slopes, and soils.
Sedimentary Rock / Alluvium
- Siltstone
- Sandstone
- Conglomerate
Alluvium environment with a mix of different textures; laid down by the river; unconsolidated materials.
Mass Wastage
- Undercutting of steep slopes
- Slumps or mass wastage – occurs at a couple of places along the Millstone
- Movement occurs downslope under the influence of gravity
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| Movement occurs downhill as waterfalls |
Glacial Debris
- Glacial till covers much of the underlying bedrock
- Visible in the more elevated wooded areas – away from the Millstone
- Debris near the Millstone has been reworked by the flow of running water
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| Tumbled rock |
Altered Flow of Millstone River - Natural Processes
- Faulting and fissuring of bedrock
- River channels flow in straighter lines (structural control)
- Provides sharp elevation differences (i.e. waterfalls)
- Volume and velocity of water flow changes with the seasons
- Material carried in suspension or moved via saltation processes further erodes, by abrasion, additional material
- River banks can be undercut, trees toppled (often with assistance of wind)
- Soils and blocks of bedrock can tumble into the channel
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| Salmon ladder |
Altered Flow of Millstone River - Human Impacts
- Construction of roads, trails, parking lots, bridges, and so on, impact rate and volume of flow into the river
- Runoff is accelerated and volume of interflow is lessened with development of impermeable surfaces
- Construction of weirs has impacts the holding back flow of water
- Construction of a fish ladder has diverted some of the flow into an artificial channel
Seasonal Variations
- Volume of water flowing down Millstone River is greater in the winter months when Nanaimo receives most of its precipitation and the temperatures are cooler (less evapotranspiration)
- Volume is less in the summer when the weather is warm and dry (greater evapotranspiration)
- Evidence of this is the scoured bedrock from flooding in winter
- Pothole development (abrasion during flood stage of the river)
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| Undercut bedrock, potholes |
Natural Processes along the Millstone
- Tectonic activity – shift in the plates causes fracturing and fissuring of underlying bedrock
- Undercutting of the river in the cutbank slopes of the valley which leads to mass wastage or slumping
- Evidence: fallen trees, slumping of soil and bedrock which is aided by gravity
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| Swollen river flowing past my Prof. |
