Tephra studies at Mount Baker
By Dave Tucker
January 8, 2007
Over the past decade, Kevin Scott (CVO-USGS) and Dave Tucker (WWU) have been gradually mapping out distributions of Holocene tephras at Mount Baker. Microprobe chemistry, thickness, grain size, many 14C dates have been obtained. A manuscript will be submitted for publication shortly. Some details have appeared in various abstracts by Scott and Tucker (see references below). Three post-glacial eruptive periods have been defined, in part based on the ages of these tephra deposits. The tephras, and the associated eruptive periods, are given in the table, below.
Tephra unit(s) / Vent / Eruptive period / Other events1 / AgeLayer SP andesite, magmatic / Carmelo Crater / unassigned / Multiple lava flows, pyroclastic flows, lahars / 10,870 BP
T12 phreatomagmatic?
T2 phreatic
T3 andesite, magmatic / T1,T2 –
Sherman Crater? / unassigned / unknown / pending
Set SC basalt, magmatic / Schreibers Meadow cinder cone / Schreibers Meadow / Sulphur Creek lava, Schreibers Meadow lahar / 8500-8850 BP
Layer MY andesite, phreatic? / Sherman Crater / unassigned / unknown / ~8100 BP
Layer OP, phreatomagmatic; Layer BA, andesite, magmatic / Sherman Crater / Mazama Park
(vent at Sherman Crater) / Park Creek lahars; Middle Fork Nooksack lahar; Boulder Creek lahar; Ridley Creek lahar / 5740-5930 BP
Set YP, phreatomagmatic / Sherman Crater / Sherman Crater / Morovitz Creek lahar; unnamed lahar in Boulder Creek / 1843-present
1 See Scott and Tucker, 2003, 2006; Scott et al, 2001, 2003a; Tucker and Scott, 2004.
2 These three layers are recently discovered, and provisionally named. Chemistry and ages are pending. Not all are necessarily Mount Baker ashes, though it seems likely that they are. T3 is conceivably the SP andesite.
We prefer to use the long-standing naming scheme used at other Cascade volcanoes, where tephra units have been named by letter designations and volcano of origin (e.g. Porter, 1978; Gardner et al., 1998; Mullineaux, 1974, 1986, 1996). Letter codes stem from field descriptions for a given tephra bed or layer; they are not otherwise systematic. Layer YP, for instance, is young and pale. Alternative unit names and brief descriptions for some of these tephra units appear in Kovanen et al., 2003. To correlate these authors’ unit names with those used in this study, Set SC = “Schreibers Meadow Scoria”; Layer OP = “Rocky Creek Ash”; and Layer BA = “Cathedral Crag Ash”.
The most significant finding to date is that the 1843 eruptions, reported by Hudson’s Bay personnel in Fort Langley, BC, produced magmatic tephra (see photomicrographs, below). The YP ash, found at the base of the soil layer, is full of clear glassy ash. Pyroclasts in the fine ash fraction typically have blocky shapes rather than the classic bubble wall shards; this texture is indicative of highly explosive magma-water interaction. The very poor sorting of the YP deposits is another feature associated with phreatomagmatism. However, black, vesicular, vitreous lapilli (2-4 mm across), clearly magmatic, are found up to 14 km from Sherman Crater. The YP ash is distributed widely; it is found at least 8 km northwest, 23 km south, 33 km southeast, and 17 km north of Sherman Crater. After the better-known BA tephra (Hildreth et al., 2003), this is the most widespread Holocene ash from Mount Baker.
This project will be the subject of a talk during the Mount Baker research symposium at the May 2007 Cordilleran GSA meeting at Western Washington University. Watch this website for further updates.
References:
See the various Scott and Tucker abstracts listed on this website for more information about the tephras and Mount Baker’s eruptive periods.
Some tephra unit names and descriptions were previously published in:
Scott, K.M., Macias, J.L., Naranjo, J.A., Rodriguez, S., and McGeehin, J.P., 2001,
Catastrophic debris flows transformed from landslides in volcanic terrains: mobility, hazard assessment, and mitigation strategies: US Geological Survey Professional Paper 1630.
The SC and BA tephras are also discussed in:
Hildreth, W., Fierstein, J., and Lanphere, M., 2003, Eruptive history and geochronology
of the Mount Baker volcanic field, Washington: Geological Society of America Bulletin, v. 115, p. 729-764.
Kovanen, D.J., Easterbrook, D.J., and Thomas, P.A., 2001, Holocene eruptive history of
Mount Baker, Washington: Canadian Journal of Earth Science, v. 38, p. 1355-1366.
Other papers referred to:
Gardner, J.E., Carey, S., and Sigurdsson, H., 1998 Plinian eruptions at Glacier Peak and
Newberry volcanoes, United States: Implications for volcanic hazards in the Cascade Range: Geological Society of America Bulletin v. 110, p.173-187.
Mullineaux, D.R., 1974, Pumice and other pyroclastic deposits in Mount Rainier National
Park, Washington: US Geological Survey Bulletin 1326, p.1-83.
Mullineaux, D.R., 1986 Summary of pre-1980 tephra-fall deposits erupted from Mount
Saint Helens, Washington State, USA: Bulletin of Volcanology, v. 48, p.17-26.
Mullineaux, D.R., (1996) Pre-1980 tephra-fall deposits erupted from Mount
Saint Helens, Washington. US Geological Survey Professional Paper 1563, p. 1-95.
Porter, S.C., 1978 Glacier Peak tephra in the North Cascade Range, Washington:
Stratigraphy, distribution, and relationship to late-glacial events: Quaternary Research, v. 10, p. 30-41.