Last week, Connie Sobchak shared a post about the “Giants” – a massive boulder field she’d come upon while exploring near the Rutherford. Hugh Naylor took us up on a invitation to share his insight about the site, in this post, that may be the first of an ongoing series.
To catch you up, here’s a quick recap from Connie:
About fourteen kilometres from Pemberton, heading south, lurks a boulder patch that is only partly visible from the road. There is a rock quarry there now and a gate prevents trespassers in vehicles but one fall day last year we stopped to see if the brushing under the hydro lines might yield some firewood. Since that first visit, I’ve gone back several times for though we got no winter fuel supply, the immensity of the rocks and the mystery of how they got there lit a fire of curiosity in me.
Now, boulders as a whole don’t interest me all that much-or they didn’t till I took a closer look-but these particular rocks immediately intrigued me because of their size and because of their location. The nearest mountain, from which said mammoths must have fallen, is about three kilometres away and it doesn’t tower over the patch as you might expect. When these rocks sprang free, they must have bounced and bounded across the landscape as if they were pebbles. It would be like watching houses roll by. Oddly, the boulders don’t seem to have broken into smaller bits but perhaps they did and my mind is not adjusting for the size factor when it comes to hunks of mountain rolling about. It is impossible to consider that they could have been even larger.
After a friend loaned me a geological study of the area, I learned that the likely cause of the landslide was either, tectonic settling, yearly cycles of freezing and thawing or a large earthquake. Though several bits of research support alternate dates for the occurrence, the study favoured a time frame between 2,200 and 3,600 years ago. It was also somewhere in this period that Mt. Meager last erupted. (Blais-Stevens, A; Hermanns, R; Jermynn, C)
Hugh was the friend, and he picks up the tale, here.
Mystery Creek “Giants”
by Hugh Naylor
As a follow up to Connie’s post I offer the following comments.
First of all what are my credentials? I’ve always loved mountains. A career in geology seemed a logical choice and to this end I spent 2 wonderful student summers with two great mentors, Drs. Souther and Wheeler in the coast mountains in the Stikine area and Rockies/ Selkirks with the Geological Survey of Canada.
After several years of travelling and working in the mineral exploration business, I was ready for a change and lapsed into a career raising children, weeding strawberries and artificially inseminating cows, with a final job as a fisheries technician which satisfied my enduring passion for fishing. Those carers didn’t pay very well but at least I was stationed close to home, which was now Pemberton.
Even though I was not a career geologist any more my fascination with the origin and development of landforms, or geomorphology, was permanently instilled. It blossomed when I found myself living at the doorstep of one of the most geologically active regions of North America.
Like Connie, I travelled the highway to Whistler thousands of times before wondering where those “giants” came from. My first stop was Google Earth. The origin and slide path are plainly seen there. I recommend to anyone to make that the first stop in their wondering.
Then serendipity took over, as it has many times in my life and I found myself at a Whistler Museum talk on potential hazards in the Sea to Sky corridor which might affect transportation at the 2010 Olympics. At that talk I learned that the “Mystery Creek Slide” was the object of major research, given that the slide path had reached the current Highway 99 location in recent historical times. (Mystery Creek is a westerly flowing tributary of the Green River adjacent and to the south of the slide path east of Green River).
Now my juices were on the move and a stop at the GSC library resulted in copies of many reports relating to the Lillooet River watershed historical geology. Then I had the accidental good fortune to meet one of the authors of several reports who suggested we do a search for evidence of a date for the slide which had not yet been conclusively determined.
Pierre Friele postulated that when the slide crossed the Green River a dam would have been formed creating a pond which would be revealed as a sedimentary layer. He was thrilled to find these deposits in exactly the right location with respect to the slide rock and further identified and sampled small bits of charcoal in the sediments. The samples were sent off to the lab for carbon dating with very interesting results. (I’ll leave you hanging on that one).
Pierre provided many more reports relating to Pemberton Valley geology.
I think there might be a story there.
What were the tectonic, volcanic and depositional events leading to the present that shaped the valley and its inhabitants in the last 10, 000 years since the melting of the last ice age?
Photo courtesy Connie Sobchak.
For more from Hugh, see: