March 18th, 2015 ~ Vol. 85 No. 11
Looking Back - John Kinnear
Mazama – The Day the Dry Snow Fell
Crowsnest Pass Herald Front Page
The spectacular Crater Lake- deepest in the United States
My father had the presence of mind to collect a sample of the ash that had coated his old Pontiac on May 19th, 1980. I keep it in an old prescription bottle as a reminder of the power of nature. It was of course volcanic ash from the catastrophic eruption of Mt. St. Helens volcano that had occurred the day before. We are about 700 kilometers northeast of what remains of St. Helens as the crow flies. As the ash flies, at apparently about 100 kilometers per hour, it theoretically took only seven or so hours for that ejection to find its way here in what was a fairly thin dusting compared to further south.
St. Helens sent an eruption column 80,000 feet into the air and blanketed 11 states. Of course the internet coverage makes little or no mention of its impact on Canada and most of the ash distribution maps end abruptly at the Canada/ US border, like there was some kind of a wall there!
The logistics of St. Helens are well known (57 people died, 2.8 billion in damages) but what is not that well known is that it is part of what they call the Cascade Volcanic Arc, a series of 20 major volcanoes and 4,000 separate volcanic vents that have been erupting for the last 38 million years along the Pacific Northwest. Names like Mt. Girabaldi, Rainier, Adams, Hood and Baker come to mind. Mt. Baker is clearly visible from Vancouver as you drive east towards Chilliwack. It is a stunningly beautiful mountain to behold.
Towards the southern end of this arc is another spectacular place called Crater Lake National Park in south-central Oregon. It is a 1,900 foot deep caldera lake that was formed about 7,700 years ago after the collapse of the Mount Mazama volcano. I first discovered Mazama in Volume 1 of Alberta Formed, Alberta Transformed, a wonderful collection of thirty distinctive essays spanning 12,000 years, that were published in 2006 as part of Alberta’s centennial. The third essay in this sequential review is entitled: “The Day the Dry Snow Fell” and using known volcanic data presents an imagined account of this natural disaster. The authors, Alwynne B. Beaudoin and Gerald A. Oetelaar, reconstruct what happened by “examining the effects of the eruption as they are preserved in the landscape.”
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Unlike the Mt. St. Helens ash map, the Mazama distribution map has a much broader reach and much more substantial depositing. Mazam’s reach was in the order of 2,000 kilometers north and east of the vent and covered an astounding 1.7 million square kilometers. The essay estimates that a layer perhaps 15 centimeters deep was left over Southern Alberta. Its widespread distribution makes it useful in archaeological studies as a horizon or time, marker. Mazama ash has a very distinctive mineralogical composition which allows it to be distinguished from other volcanic ash deposits. Radio carbon dating from charcoal from within or adjacent to the ash layer dates the ash to between 7,640 and 7,620 years ago and this was further verified in Greenland. Yup, the ash made it that far and counting annual ice layers in ice-core from the Greenland ice cap puts it at 7,627 years ago (with an uncertainty of plus or minus 150 years!)
Just imagine what it must have been like to have been out on the prairies 7,700 years ago and see that looming cloud of ash racing towards you. The effects of this heavy coating of tephra on vegetation and drinking water must have been substantial and long lasting. Animals and peoples of the area would have been on the move for some time seeking new sources of food and water. The Mazama ash in Southern Alberta is very fine-grained, almost like flour. Try to imagine what it was like, with winds and rain stirring up and redepositing and moving this amount of material around.
We know that some ash carried up high in the atmosphere remains suspended for weeks and months after the event and is carried around the world by upper atmospheric winds. There is would have affected temperatures, blocking sunlight. That first winter must have been a nasty one and on the prairies no doubt the ash had buried and crushed most foliage and affected most plant’s ability to photosynthesize and reproduce berries and seeds. The ash would have: “affected all aspects of life for people in Southern Alberta for many years.”
The essay mentions a horizon (time) marker from a 2004 archaeological excavation in the Cypress Hills called “Stampede site (DjOn-26).” The Mazama ash layer found there had a thick, distinctive layer. Beneath the ash layer lots of evidence of peoples coming back to the area again and again, camping there as it offered food, shelter, lodgepole pine trees for tipi poles and fresh water. Above the Mazama ash layer there is a considerable gap with no evidence of human occupation. Some suggest as long as seven hundred years!
As I write this piece on this early Sunday afternoon the forecasted heavy snow event is happening big time and the snow is coming straight down and fast. I am trying to imagine what the early peoples of Southern Alberta must have been thinking when the “Day the Dry Snow” happened. The Krakatoa eruption in 1883 was heard as far as 4,700 kilometers away. I wonder what they thought on that early autumn day when the sound of Mazama came thundering over the prairies.
An interesting side note. Years ago a geologist mentor handed me an unusual piece of coal and informed me that it had “tonstein” or ancient volcanic ash bands in it. I soon came to realize that it was often found in coal seams which were originally swamps where the ash would have accumulated undisturbed and eventually pressured into a compact sedimentary rock with a very distinctive characteristic and appearance. While obviously not very thick they proved to be, nevertheless, the perfect way to correlate coal seams.
How remarkable that part of my career at a coal mine would involve tracking volcanic ash layers 140 million years old. It seems that this business of dry snow has been around a long long time.
March 18th ~ Vol. 85 No. 11
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