What is tephrochronology?


Glacier Peak and Mt. St. Helens tephras
in laminated lake sediments at Marias Pass, MT


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.

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, in at least one bog in eastern North America, in ocean floor sediments, and more than 5,000 km from it's source in Greenland ice.

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 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 employed. 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 SiO2, TiO2, Al2O3, FeO, MnO, MgO, Na2O, K2O, P2O5, and Cl. Additional components (e.g. BaO, Cr2O3, SrO, V2O3, ZrO2, and F) may also be quantified when needed. For quality control purposes, secondary standard glasses including Lipari obsidian and BHVO-2g are routinely analyzed with the unknowns in the same analytical session. 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.

Recent Publications

  • 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 Article online
Glacial ice core from Mt. Logan, Yukon Territory, Canada.
Several tephras have been found in this core.
  • 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 Article  online - Coordinate Transform Spreadsheet
  • 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.  Supplemental figures with captions plus captions for the supplemental tables: High-resolution version (35 MB)  Screen-resolution version (3.3 MB).
  • 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. Article online
  • 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. Article online. Supplemental materials: Fig S1 (location map), Table S1 (tephra localities), Table S2 (spreadsheet containing microprobe data), Table S3 (radiocarbon dates), Supplemental references and bibliography.

Recent Conference Proceedings

  • 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. Abstract  -  Conference Poster
  • 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. Abstract

Recent tephrochronology meetings, conference sessions, special volumes, etc.