The Mazama Ash (formally named the Mazama Member in some areas) is an extensive, geologically recent deposit of

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...

that is present throughout much of northern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. The ash was ejected from

Mount Mazama Mount Mazama (''Giiwas'' in the Native American language Klamath) is a complex volcano in the state of Oregon, United States, in a segment of the Cascade Volcanic Arc and Cascade Range. Most of the mountain collapsed following a major erupt ...

, a

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

in south-central

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

, during its climactic eruption about 7640 ± 20 years ago when

Crater Lake Crater Lake ( Klamath: ''Giiwas'') is a volcanic crater lake in south-central Oregon in the western United States. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The lake partly fill ...

was formed by

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

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 The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equi ...

.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. Because it was deposited throughout a wide area at a known time, the Mazama Ash is an important

marker bed Marker horizons (also referred to as chronohorizons, key beds or marker beds) are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no do ...

for

paleoclimatology Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...

paleoecology Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...

, and

archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsc ...

, as well as for

Quaternary geology Quaternary geology is the branch of geology that study developments from 2.6 million years ago onwards. In particular, Quaternary geology study the process and deposits that developed during the Quaternary, a period characterized by glacial-intergl ...

and

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

correlation.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.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. The ash particles and gasses from the Mazama eruption would have caused climate cooling for a period of several years after the eruption. Throughout the northern

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, a ...

, 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.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.

Age

The climactic eruption of Mount Mazama during which the Mazama Ash was ejected occurred approximately 6790 ± 15 ¹⁴C yrs BP, or 7640 ± 20 calibrated years

Before Present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Beca ...

(5677 ± 150 B.C.E.), based on analysis of multiple ash and

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they r ...

sources throughout the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Thou ...

, as well as by other methods such as identification of ash from within an

ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ...

from the

Greenland Ice Sheet Project The Greenland Ice Sheet Project (GISP) was a decade-long project to drill ice cores in Greenland that involved scientists and funding agencies from Denmark, Switzerland and the United States. Besides the U.S. National Science Foundation (N ...

and from sediment cores from the

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...

basin.

Distribution

The Mazama ash spread over an area of at least in the northern Great Plains, where it is most commonly preserved within

peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

, and aeolian

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

s.David, P.P. 1970. Discovery of Mazama Ash in Saskatchewan, Canada. Canadian Journal of Earth Sciences, vol. 7, p. 1579-1583. In the U.S., it is present in portions of the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...

s of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

Idaho Idaho ( ) is a U.S. state, state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Monta ...

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

and

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

.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. It is also present in the Greenland ice sheet, and in marine sediments off the coast of

, and southernmost

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

. In

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

, deposits of Mazama Ash several centimeters thick are commonly present in southern areas of

,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.

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

, and

Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North Dak ...

. 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. Shards of volcanic glass from the Mazama Ash have also been identified in the sediments of

and in a bog in Newfoundland.

Composition and identification

The Mazama ash includes

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With th ...

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

clinopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...

, and

volcanic glass Volcanic glass is the amorphous solid, amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the closely packed, highly ordered array of a crystal and the highly disorde ...

.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. It can be distinguished from other volcanic ash deposits, such as those from eruptions of

Glacier Peak Glacier Peak or Dakobed (known in the Sauk-Suiattle dialect of the Lushootseed language as "Tda-ko-buh-ba" or "Takobia") is the most isolated of the five major stratovolcanoes (composite volcanoes) of the Cascade Volcanic Arc in the U.S state ...

Mount St. Helens Mount St. Helens (known as Lawetlat'la to the indigenous Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United St ...

and Mount Rainier, by the unique chemistry of those constituents. This can be determined by

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It ...

analysis, by the

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

of the volcanic glass, and by

neutron activation Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emit ...

analysisTheisen, 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. and similar techniques. Radiocarbon dating of associated carbon-bearing material may also aid identification of the Mazama Ash.

Impact

Comparison with the effects of the

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. 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 Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

during the eruption may also have led to substantial depletion of stratospheric

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

References

{{reflist Geologic formations of British Columbia Geologic formations of Alberta Geologic formations of Saskatchewan Geologic formations of California Geologic formations of Oregon Geologic formations of Washington (state) Geologic formations of Idaho Geologic formations of Montana Geologic formations of Nevada Geologic formations of Wyoming Geologic formations of Utah VEI-7 eruptions Volcanic eruptions in the United States Plinian eruptions

Age

Distribution

Composition and identification

Impact

See also

References