HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) An erratum has been published Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Porter, S. C. Articles by Swanson, T. W. Search for Related Content Articles by Porter, S. C. Articles by Swanson, T. W. GeoRef GeoRef Citation

³⁶Cl dating of the classic Pleistocene glacial record in the northeastern Cascade Range, Washington

Stephen C. Porter and Terry W. Swanson

Department of Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, Washington 98195-1310, USA

Corresponding author: E-mail address: scporter{at}u.washington.edu

Surface-exposure ages of granodioritic and gneissic boulders on seven successive moraines record the Late Pleistocene history of a major glacier system in the northeastern Cascade Range of Washington. The youngest moraines are boulder-rich and sharp-crested, but successively older moraines have lower boulder frequencies and are more degraded. Seventy-six ³⁶Cl dates for the moraines cluster in groups having mean ages (± 1) of 12,500 ± 500, 13,300 ± 800, 16,100 ± 1100, 19,100 ± 3000, 70,900 ± 1500, 93,100 ± 2600, and 105,400 ± 2200 years; a still-older, highly weathered and eroded moraine is undated, but likely is at least 165,000 years old. The moraine ages and relative extent of the Icicle Creek glacier correspond closely to the ages and relative amplitude of July insolation minima at 47.5° N latitude. They also are in accord with ages for glaciations in the European Alps that were inferred by Milutin Milankovitch and colleagues in the 1920s based on calculations of summer insolation. Evidence that the greatest Late Pleistocene glacier advance occurred at the onset of the last glaciation (during marine isotope substage 5d) is consistent with a cooling climate and major glacier advances at that time elsewhere in North America and the Eurasian Arctic, with a dramatic increase in global ice volume, and with the shifting track of the jet stream over northwestern United States.

This article has been cited by other articles:

				S. C. Porter and T. W. Swanson 36Cl dating of the classic Pleistocene glacial record in the Northeastern cascade range, Washington Am J Sci, June 1, 2008; 308(6): 813 - 813. [Full Text] [PDF]