Skip to Main Content
Book Chapter

Hot clasts and cold blasts: thermal heterogeneity in boiling-over pyroclastic density currents

By
Erika Rader
Erika Rader
Department of Geological Sciences, University of Idaho, 825 West 7th Street, 322 Mines Building, PO Box 443022, Moscow, ID 83844-3022, USA
Search for other works by this author on:
Dennis Geist
Dennis Geist
Department of Geological Sciences, University of Idaho, 825 West 7th Street, 322 Mines Building, PO Box 443022, Moscow, ID 83844-3022, USA
Search for other works by this author on:
John Geissman
John Geissman
Department of Earth and Planetary Sciences, MSC 03 2040, 1 University of New Mexico, Albuquerque, NM 87131-0001, USAPresent address: Department of Geosciences, ROC 21, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, USA
Search for other works by this author on:
Joe Dufek
Joe Dufek
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive Atlanta, GA 30332, USA
Search for other works by this author on:
Karen Harpp
Karen Harpp
Department of Geology, Colgate University, 13 Oak Drive, Hamilton, NY 13346, USA
Search for other works by this author on:
Published:
January 01, 2015

Abstract

Partial thermal remanent magnetization data from clasts in pyroclastic density current (PDC) deposits provide information on the emplacement temperatures of both lithic and juvenile magmatic clasts contained in the deposits. We collected palaeomagnetic data from clasts in PDC deposits emplaced during historical eruptions of two volcanoes in Ecuador, the 2006 eruption at Tungurahua and the 1877 eruption at Cotopaxi. These eruptions were characterized by emplacement of PDCs mainly related to boiling-over activity. The deposits of these eruptions are similar and are characterized by cauliflower-textured juvenile scoria clasts up to 1 m in diameter and a diverse assemblage of lithic clasts surrounded by an unwelded ashy matrix. On the basis of progressive thermal demagnetization experiments, we infer that emplacement temperatures for most of the lithic clasts in PDC deposits are below 90 °C. In contrast, palaeomagnetic data from juvenile clasts from the same deposits provide emplacement temperatures higher than 540 °C. These data indicate the PDC were thermally heterogeneous over short length scales (decimetres) also after deposition. We hypothesize that PDCs emplaced by the boiling-over mechanism cool quickly owing to atmosphere entrainment, causing the juvenile clasts to form a rind that retains heat and that also prevents lithic clasts from appreciable heating. Several deposits on Cotopaxi, despite being morphologically similar to the PDC deposits, contain both cold lithic and juvenile clasts, which we interpret to be lahar deposits formed by PDCs travelling across glacial ice and snow. Rare deposits containing both hot lithic and hot juvenile clasts are classified as well-mixed, hot PDCs, and were erupted during a more energetic phase at Tungurahua.

You do not currently have access to this article.

Figures & Tables

Contents

Geological Society, London, Special Publications

The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes

M. H. Ort
M. H. Ort
Search for other works by this author on:
M. Porreca
M. Porreca
Search for other works by this author on:
J. W. Geissman
J. W. Geissman
Search for other works by this author on:
Geological Society of London
Volume
396
ISBN electronic:
9781862396722
Publication date:
January 01, 2015

GeoRef

References

Related

Citing Books via

A comprehensive resource of eBooks for researchers in the Earth Sciences

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal