One day in early December I noticed this rock at trail side along the Mamquam Blind Channel. I had passed that spot dozens of times in the past two years, so why had I not seen the rock previously? I concluded that light at a low angle in late afternoon and recent rains after a dry summer and fall were responsible for the tapestry-like appearance that caught my attention.
I wanted to know more about how long the rock might have been weathering in that place, and what could be responsible for the colours I was seeing. I ended up consulting a geologist, a lichenologist, and a historian. I also found a research paper that discusses how algae can affect the rate of erosion in rocks containing carbon.
Here is the possible story I’ve pieced together, starting with a reply from the geologist. “The rock looks to be a pyroclastic volcanic flow, most likely formed during eruption of the Nch’Kay’ volcanic complex more than 13,000 years ago. The pattern of silica veining and disruption of coarser-grained fragments suggests that they were previously cooled and later incorporated into a lava or ash flow represented by the finer-grained material. Mineralization associated with eruption and cooling of the lava flow may explain the variegated pattern of lichen growth.” The historian shared a newspaper clipping from 1963. It showed that the rock would have been broken off during clearing for a roadway, so it seems the weathering has taken place over just 62 years. The lichenologist agreed with my thought that the growth on the surface is likely algae. I suggested that because of the rapid colour changes I observed during a two-week rainy stretch: the red colour became much more pronounced. The paper I mentioned describes how terrestrial algae has been shown to speed up the rate of erosion of carbonate rock by three times. It all seems to make sense, and of course I’m left with other questions. You may have more.
To me, this rock tells a tale of earth science meeting life science in the beginnings of soil building. The more I learn about biodiversity, the more beauty I see.
Gwen
The banner photo shows detail from the upper right quadrant of the rock. Can you find the spot?