Tephrochronology is the use of volcanic ash and pumice (tephra) as a tool for dating and correlation. Tephrochronology is employed globally with numerous interdisciplinary applications including: environmental and climate change, archaeology, Earth surface processes, ecology, animal and plant evolution, earthquake hazards & neotectonics, volcanic hazards, and even medicine. In recent years, tephrochronology has been a fast-growing discipline, in part because it is considered one of the few techniques with the potential to significantly reduce chronological uncertainties in archaeological and environmental research. Tephrochronology has also expanded to include trace concentrations of volcanic ash invisibly hidden in sediments. Such cryptotephra deposits extend the range of tephra correlation to sites thousands of kilometers away from volcanic sources, even enabling correlations across oceans and between continents.
Because volcanic ash is rapidly and widely dispersed during large, explosive eruptions, tephrochronology provides a unique capability to tie together records of, for example, environmental change over long distances and connect land, lake, sea, and glacial ice records with a temporal resolution that is largely unmatched by other dating techniques. For example, ash from the large eruption which formed Crater Lake in Oregon has been identified at hundreds of locations in western North America, at a few sites in eastern North America, in ocean floor sediments, and more than 5,000 km from it’s source in Greenland ice. Similarly, White River ash from Alaska has been found as far away as Europe.
The electron microprobe is the primary analytical tool for tephrochronology. It is most commonly used to analyze the glass fraction of tephra for major and minor element abundances and thereby provide a chemical fingerprint which often allows ash from different eruptions to be uniquely identified. Mineral abundances, mineral compositions, particle size and shape, layer thickness, trace-element abundances in the glass, stratigraphic relations, and dating are also used. Tephra correlations are most robust when multiple lines of evidence are combined.
The CU Tephra Lab
The tephra lab uses the ARL-SEMQ microprobe as the primary tool for chemical fingerprinting. Samples are typically mounted using low-viscosity epoxy in a 2.54 cm / 1 inch diameter acrylic disk, polished, carbon coated, and then placed in the microprobe for analysis. Samples are routinely analyzed for eleven major and minor elements/oxides: SiO2, TiO2, Al2O3, FeO, MnO, MgO, Na2O, K2O, P2O5, BaO, and Cl. A separate analytical procedure is also available which includes twenty major, minor, and trace elements/oxides: SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, Cl, BaO, CoO, Cr2O3, NiO, Rb2O, SO3, SrO, VO2, and ZrO2. For quality control purposes, four reference glasses (Lipari obsidian ID3506, BHVO-2g, NKT-1g, and orthoclase glass) are routinely analyzed with tephra samples in the same analytical session. To enhance accuracy and precision, several advanced techniques are also employed, including a time-dependent intensity correction for sodium, mean atomic number backgrounds, combined EDS+WDS acquisition, blank corrections, and spectral interference corrections.
The resulting data may then be used to identify tephra samples by comparison with a large database containing analyzes from thousands of tephra samples, mostly from North America. The laboratory also has a large reference collection including, for example, proximal samples of most major tephra-producing eruptions of Mt. St. Helens (WA) and Newberry Volcano (OR) and samples from key distal reference locations like Summer Lake (OR). In cases where there are several potential matches with very similar chemical fingerprints, the unknown sample and reference samples may be analyzed together in the same session on the microprobe for confirmation.
Tephra identification is available as a service to external clients. Please contact us for further information.
Analytical Accuracy and Precision
Based on analysis of reference glasses with a range of compositions, the accuracy, precision, and long-term reproducibility of the CU tephra lab’s data is excellent. For some elements, the current analytical precision exceeds that of most tephra labs which submitted data to the 2011 INTAV interlaboratory comparison (Kuehn et al., 2011). The CU tephra lab is also one of only a few which routinely reports data for both P and Ba. Several examples are shown below. A complete reporting of CU tephra data compared to the INTAV submissions is also available. For tabulated results from a number of international reference glasses, see the Quality Control page of this website.
Zander, P.D., Kaufman, D.S., McMay, N.P., Kuehn, S.C., and Henderson, A.C.G, 2017, Using correlated tephras to refine radiocarbon-based age models, upper and lower Whitshed Lakes, south-central Alaska. Quaternary Geochronology, DOI: 10.1016/j.quageo.2018.01.005
Lowe, D.J., Pearce, N.J.G., Jorgensen, M.A., Kuehn, S.C., Tryon, C.A., & Hayward, C.L., 2017, Correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods: review and evaluation. Quaternary Science Reviews, 175, 1-44 DOI: 10.1016/j.quascirev.2017.08.003
Pyne-O’Donnell, S.D.F, Cwynar, L.C., Jensen, B.J.L., Vincent, J.H., Kuehn, S.C., Spear, R., Froese, D.G., 2016, West Coast volcanic ashes provide new continental-scale late-glacial time horizons: Quaternary Science Reviews 142, 16-25, DOI: 10.1016/j.quascirev.2016.04.014
Zander, P.D., Kaufman, D.S., Kuehn, S.C., Wallace, K.L., and Anderson, R.S., 2013, Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska: Journal of Quaternary Science, 28, 8, pp. 761-771, DOI: 10.1002/jqs.2671
Pyne-O’Donnell, S.D.F, Hughes, P.D.M., Froese, D.G., Jensen, B.J.L., Kuehn, S.C., and eight others, 2012, High-precision ultra-distal Holocene tephrochronology in North America, Quaternary Science Reviews, 52, pp. 6-11, DOI: 10.1016/j.quascirev.2012.07.024
Kuehn, S.C., Froese, D.G., and Shane, P.A.R., 2011, The INTAV intercomparison of electron-beam microanalysis of glass by tephrochronology laboratories, results and recommendations: Quaternary International. doi:10.1016/j.quaint.2011.08.022
Kuehn, S.C. and Froese, D.G., 2010, Tephra from ice – A simple method to routinely mount, polish, and quantitatively analyze sparse fine particles: Microscopy and Microanalysis
Kuehn, S.C. and Negrini, R.N., 2010, A 250,000-year record of Cascade Range pyroclastic volcanism from late Pleistocene lacustrine sediments near Summer Lake, Oregon, USA: Geosphere.
Lacelle, D., St-Jean, M., Lauriol, B., Clark, I.D., Froese, D., Kuehn, S.C., Zazula, G., and Lewkowicz, A., 2009, Burial history of a relict perennial snowbank body and vegetation by the Dawson tephra (25,300 14C years BP) near Red Creek, Ogilvie Mountains, central Yukon, Canada: Quaternary Science Reviews.
Kuehn, S.C., Froese, D.G. Carrara. P.E., Foit, F.F., Pearce, N.J., and Rotheisler, P., 2009, The latest Pleistocene Glacier Peak tephra set revisited and revised: major- and trace-element characterization, distribution, and a new chronology in western North America: Quaternary Research, vol. 71, pp. 201–216.
Kuehn, S.C., 2017, Critical Topics in Geochemical Analysis of Tephras: IAVCEI 2017 Scientific Assembly, Portland, Oregon, USA, Workshop: Best Practices in Tephra Collection, Analysis, and Reporting: Leading Toward Better Tephra Databases Workshop.
Kuehn, S.C., Arrington, E., Rose, J., Frye, J., Ballengee, S., Hostetler, A., and McNeely, C., 2017, Pyroclastic eruptive history of the Three Sisters volcanic cluster, Cascade arc, Oregon, USA: IAVCEI 2017 Scientific Assembly, Portland, Oregon, USA.
Rose, J.W. and Kuehn, S.C., 2017, Expanded and Revised Tephrochronology for the 220,000-Year Record From Carp Lake, Washington, USA: Geological Society of America Abstracts with Programs. Vol. 49, No. 3, DOI 10.1130/abs/2017SE-290740
Kuehn S.C., 2016, Routine EPMA of Silicate Glasses using a 5 Micron Beam: Taking Advantage of TDI, Combined EDS+WDS, MAN, and a Multi-standard Blank Correction: Electron Probe Microanalysis Topical Conference (EPMA 2016), Madison, WI, DOI: 10.13140/RG.2.1.2656.0882
Kuehn S.C., Hostetler A.J., and Ballengee S.J., 2015, Records of lake level fluctuations, faulting, and volcanism from Summer Lake, Oregon, USA. Sixth International Limnogeology Congress (ILIC6) – Abstract Volume, Reno, Nevada, June 15-19, 2015, USGS Open-File Report 2015-1092, pp. 120-121.
Wallace K, Bursik M.I., and Kuehn S.C., 2015, Best-practice checklists for tephra collection, analysis and reporting – a draft consensus from the Tephra 2014 workshop: American Geophysical Union Fall Meeting paper V51F-3108. DOIL 10.13140/RG.2.2.24067.30248
Kuehn S.C., Deino, A.L., Hostetler A.J., and Ballengee S.J., 2015, Potential for a Three-Million-Year Record of Lake Level, Climate, and Volcanism from Summer Lake, Oregon, USA: Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p.754. DOI: 10.13140/RG.2.2.16891.92965
Ballengee, S.J., Kuehn, S.C., Koutrouli, A., Anastasakis, G., Piper, D.J.W., and Pe‐Piper, G., 2015, Holocene to Pleistocene Tephrochronology of Eleven Marine Sediment Cores from the Aegean Sea. Geological Society of America Abstracts with Programs. Vol. 47, No. 2, p.75
Hostetler, A.J., Ballengee, S.J., and Kuehn, S.C., 2015, Tephrochronology of Faulted, Fossil-Bearing, Holocene to Pliocene Sediments near Summer Lake, Oregon. Geological Society of America Abstracts with Programs. Vol. 47, No. 2, p.75
Kuehn, S.C., Pouget, S.,Wallace, K., and Bursik, M.I., 2014, Results of the Tephra 2014 Workshop on Maximizing the Potential of Tephra for Multidisciplinary Science: American Geophysical Union Fall Meeting, paper V31C-4758. DOI: 10.13140/RG.2.1.2454.0002
Kuehn, S.C., 2014, Reducing uncertainty in tephra correlation through improved geochemical characterization and better data reporting practices: Tephra 2014 Workshop
Ramsey, S.C. and Kuehn, S.C., 2015, Deciphering the Early Eruptive History of Mount St. Helens Using Microanalytical Geochemistry. Geological Society of America Abstracts with Programs. Vol. 47, No. 2, p.72
Kuehn, S.C., Bursik, M.I., and Pouget, S., 2013, Improved integration and discoverability of tephra data for multidisciplinary applications: In proceeding of the American Geophysical Union Fall Meeting, San Francisco, CA.
Kuehn, S.C., Kalteyer, D.A., and Negrini, R.M., 2013, New tephras from old sites: Examples from Carp Lake, Washington, and Summer Lake, Oregon, USA: CANQUA-CGRG Conference, Edmonton, Alberta, Canada, Aug 18-22.
Kuehn, S.C, Froese, D.G., and Shane, P, 2011, Assessing microanalytical performance using secondary standards: Results of an electron probe interlaboratory comparison using four natural volcanic glasses. Microscopy & Microanalysis 2011, Nashville, TN.
Froese, D.G., Kuehn, S.C, Fisher, D., Zdanowicz, C, Atkins, C, Dunning, H, and Jensen, B, 2010, Establishing independent age models for ice cores using tephrochronology: International Field Conference and Workshop on Tephrochronology, Volcanism and Human Activity, Kirishima, Japan.
Schupack, B.B., Miller, G.H., Kuehn, S.C., 2009, Pushing the Limits of Volcanic Cryptotephra Detection in the High Arctic, Spitsbergen, Svalbard: GSA Abstracts with Programs, V. 41, No. 7, Abstract No. 159929.