| Mazama Ash | |
|---|---|
| Stratigraphic range: Holocene | |
| Type | Member[1] |
| Unit of | Mount Mazama Formation[2] |
| Sub-units | Tsoyawata Bed, Mazama Bed[2] |
| Location | |
| Region | Northern North America |
| Country | United States, Canada, Greenland |
| Type section | |
| Named for | Mount Mazama |
| Named by | B.N. Moore, 1934.[3] |
The Mazama Ash (formally named the Mazama Member in some areas)[1] is an extensive, geologically recent deposit of volcanic ash that is present throughout much of northern North America. The ash was ejected from Mount Mazama, a volcano in south-central Oregon, during its climactic eruption about 7640 ± 20[4] years ago when Crater Lake was formed by caldera collapse. The ash spread primarily to the north and east due to the prevailing winds, and remnants of the ash have been identified as far northeast as the Greenland ice sheet.[5]
Because it was deposited throughout a wide area at a known time, the Mazama Ash is an important marker bed for paleoclimatology, paleoecology, and archaeology, as well as for Quaternary geology and stratigraphic correlation.[6][7][8]
The ash particles and gasses from the Mazama eruption would have caused climate cooling for a period of several years after the eruption.[5] Throughout the northern Great Plains, the ash would have darkened the sky and a layer of ash at least several centimeters thick would have blanketed much of the landscape, causing severe disruptions for the native people and wildlife.[7][9]
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Mount Mazama Ash from Crater Lake volcano eruption 7,700 years ago
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From Volcanoes to Lakes: Oregon's Crater Lake
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Bishop Tuff Volcanic ash rock
Transcription
I-90 east of Kittitas near the old Milwaukee Railroad trestle. The freeway rolls through Johnson Canyon here, but look carefully at Milepost 119. It's gonna go by quick! A brilliant white layer just above the creek bed. What is it? There are plenty of white layers this side of Snoqualmie Pass. Is it Diatomite - a lake bed deposit made of microscopic hard-shelled algae? How about Caliche - a hardpan mineral deposit below soil level? Or maybe a volcanic mudflow like we saw back at Thorp? Nope! This is volcanic ash. Blown downwind from the Cascades. This is not just any volcanic ash. This is the famous Mazama ash from southern Oregon! A Mount Rainier-like volcano, Mount Mazama, blew itself up 7,700 years ago, and left Crater Lake National Park. That's 300 miles from here! Ash from the mountain spread over the Pacific Northwest, 43 times more ash than the Mount Saint Helens blanket in 1980. In this creek bed, the Mazama ash is 4 inches thick. And the 1980 Saint Helens ash is less than a quarter inch of ash. Think of how much trouble we had in 1980 with a quarter inch. How did the local Native Americans deal with 4 inches? The Mazama Ash is king out here. No other ash bed rivals its regional thickness. A useful time marker used across the Pacific Northwest. There's even Mazama ash in seafloor cores off the coast of Washington. The Columbia River hauled the ash out there. On the sea bed, sitting above the Mazama ash, are 13 sandy deposits that were created by 13 tsunami-triggering magnitude 9 earthquakes that struck repeatedly over the last 7,700 years. Here in Johnson Canyon, the Mazama has quiet deposits on top of it. This is loess, wind-blown silt, sitting on top of the Mazama. But a newly-discovered fault that has broken the Mazama ash bed here means young magnitude 7 earthquakes have jolted eastern Washington since the Ice Age.
Age
The climactic eruption of Mount Mazama during which the Mazama Ash was ejected occurred approximately 6790 ± 15 14C yrs BP, or 7640 ± 20[4] calibrated years Before Present (5677 ± 150 B.C.E.), based on analysis of multiple ash and tephra sources throughout the Pacific Northwest, as well as by other methods such as identification of ash from within an ice core from the Greenland Ice Sheet Project[5] and from sediment cores from the Lake Superior[10] basin.
Distribution
The Mazama ash spread over an area of at least 900,000 km2 (350,000 sq mi) in the northern Great Plains, where it is most commonly preserved within peat, alluvial, lacustrine, and aeolian sediments.[11]
In the U.S., it is present in portions of the U.S. states of California, Oregon, Washington, Idaho, Montana, Nevada, Wyoming and Utah.[8]
It is also present in the Greenland ice sheet,[5] and in marine sediments off the coast of Oregon, Washington,[12] and southernmost British Columbia.
In Canada, deposits of Mazama Ash several centimeters thick are commonly present in southern areas of British Columbia,[13] Alberta, and Saskatchewan.[11] In southern Alberta, about 1000 kilometers (about 600 miles) northeast of the eruption site, the Mazama Ash is typically found as a white band located several metres below the present ground surface.[9] Shards of volcanic glass from the Mazama Ash have also been identified in the sediments of Lake Superior and in a bog in Newfoundland.[6]
Composition and identification
The Mazama ash includes plagioclase, hypersthene, magnetite, hornblende, clinopyroxene, and volcanic glass.[14] It can be distinguished from other volcanic ash deposits, such as those from eruptions of Glacier Peak, Mount St. Helens and Mount Rainier, by the unique chemistry of those constituents.[15] This can be determined by electron microprobe analysis, by the refractive index of the volcanic glass,[11] and by neutron activation analysis[15] and similar techniques. Radiocarbon dating of associated carbon-bearing material may also aid identification of the Mazama Ash.[11]
Impact
Comparison with the effects of the Mount St. Helens eruption of 1980 indicates that the Mazama Ash would have covered the landscape in a blanket up to 15 cm (6 in) thick, coating vegetation and clogging watercourses throughout the ashfall area. This would have caused an immediate scarcity of resources for the native people and wildlife, necessitating the movement of people out of the main ashfall area. Available archeological evidence from a site in the Cypress Hills of southern Alberta suggests a hiatus in human occupation of the ash-affected area there of perhaps 200 years.[7][9]
The particles and gasses released during the Mazama eruption caused climate cooling. Studies of the Greenland ice core suggest that the eruption produced a substantial stratospheric aerosol loading spread over a period about 6 years. This may have produced a temperature depression of about 0.6 to 0.7 °C at mid to high northern latitudes for 1 to 3 years. The release of chlorine during the eruption may also have led to substantial depletion of stratospheric ozone.[5]
See also
References
- ^ a b National Geological Map Database. "Geologic Unit: Mazama". Retrieved 2 March 2020.
- ^ a b Jonathan Ogden Davis (1978), Quaternary tephrochronology of the Lake Lahontan area, Nevada and California, ASIN B0006WYF4O, Wikidata Q63856078
- ^ Moore, B.N. 1934. Deposits of possible Nuee ardente origin in the Crater Lake region, Oregon. Journal of Geology, vol. 42, p. 353-375.
- ^ a b Egan, Joanne; Staff, Richard; Blackford, Jeff (2015-03-25). "A high-precision age estimate of the Holocene Plinian eruption of Mount Mazama, Oregon, USA". The Holocene. 25 (7): 1054–1067. doi:10.1177/0959683615576230. ISSN 0959-6836.
- ^ a b c d e Zdanowicz, C.M., Zielinski, G.A. and Germani, M.S. 1999. Mount Mazama eruption: Calendrical age verified and atmospheric impact assessed. Geology, vol. 27, no. 7, p. 621-624.
- ^ a b Spano, N.G., Lane, C.S., Francis, S.W. and Johnson, T.C. 2017. Discovery of Mount Mazama cryptotephra in Lake Superior (North America): Implications and potential applications. Geology, vol. 45, p. 1071-1074.
- ^ a b c Oetelaar, G.A. and Beaudoin, A. 2005. Darkened skies and sparkling grasses: The potential impact of the Mazama ash fall on the northwestern Plains. Plains Anthropologist, vol. 50, no. 195, p. 285-305.
- ^ a b White, J.M. and Osborn, G. 1992. Evidence for a Mazama-like tephra deposited ca. 10 000 B.P. at Copper Lake, Banff National Park, Alberta; Fig. 1 (inset), p. 53. Canadian Journal of Earth Sciences, vol. 29, p. 52-62.
- ^ a b c Beaudoin, A. and Oetelaar, G.A. 2014. Investigating the environmental impacts and cultural responses to the Mazama ashfall on the northern Plains. Geological Society of America, Abstracts with Programs, vol. 46, no. 6, p. 460.
- ^ Spano, N.G.; Lane, C.S.; Francis, S.W.; Johnson, T.C. (2017-12-01). "Discovery of Mount Mazama cryptotephra in Lake Superior (North America): Implications and potential applications". Geology. 45 (12): 1071–1074. doi:10.1130/G39394.1. ISSN 0091-7613.
- ^ a b c d David, P.P. 1970. Discovery of Mazama Ash in Saskatchewan, Canada. Canadian Journal of Earth Sciences, vol. 7, p. 1579-1583.
- ^ Nelson CH; Kulm LD; Carlson PR; Duncan JR (1 July 1968). "Mazama ash in the northeastern pacific". Science. 161 (3836): 47–49. doi:10.1126/SCIENCE.161.3836.47. ISSN 0036-8075. PMID 17756513. Wikidata Q42101098.
- ^ Debret, M., Desmet, M., Balsam, W., Copard, Y., Francus, P. and Laj, C. 2006. Spectrophotometer analysis of Holocene sediments from an anoxic fjord: Saanich Inlet, British Columbia, Canada. Marine Geology, vol. 229, p. 15-28.
- ^ Kittleman, L.R. 1973. Mineralogy, correlation, and grain-size distributions of Mazama tephra and other post-glacial pyroclastic layers, Pacific Northwest. GSA Bulletin, vol. 84, no. 9, p. 2957-2980.
- ^ a b Theisen, A.A., Borchardt, G.A., Harward, M.E. and Schmitt, R.A. 1968. Neutron activation for distinguishing Cascade Range pyroclastics. Science, vol. 161, p. 1009-1011.
This page was last edited on 11 April 2024, at 15:40