T142 Soils and Geomorphology: In Memory of Pete Birkeland

Tuesday, 11 October 2022
8:00 AM - 12:00 PM
Mile High Ballroom 2C

SKIING AND PEDALING FOR GEOLOGIC STUDIES WITH PETER BIRKELAND—SOME EXAMPLES FROM THE FRONT RANGE AND BEYOND

Paper number: T142-12
Program: Technical Sessions
Time: 10:40 AM – 10:55 AM

Authors

Abstract

Peter Birkeland combined his great loves for skiing, bicycling, and spectacular local geology to study glacial and climate history near the Continental Divide, and soil geomorphology in the Colorado Front Range (CFR). Summer hiking trips to measure water depth in alpine lakes employed a small rubber boat that resided at the Birkeland cabin. Winter reconnaissance ski trips helped guide coring sites on alpine lakes and relatively safe passage through avalanche-prone slopes, followed by actual sediment coring using lake ice as a platform before the long downhill ski run out with the cores and heavy equipment. In the summer months, slow uphill bike climbs allowed for identification and initial mapping of weathering features. Detailed work such as soil description and sample collection required long stops, but bedrock weathering criteria (Clayton technique) could be mapped while riding. Gated roads beckoned additional study for those on bicycles. Results helped guide detailed laboratory research, publication and field trip stops for universities and national meetings.

Many deep lakes near the Continental Divide could be sampled by single 3-meter drives using a Reasoner percussion corer, with one notable exception—Lake Dorothy. Coring at most sites extended to inorganic silt and clay at the core bottoms. However the L. Dorothy core recovered with Pete in 1991 reached only the lowermost organic mud with 14C dating of 10,910 14C yr BP, much younger than the 12,000+ 14C yr basal ages from other CFR lakes. Beyond the glacial limit, Pete’s bike mapping indicated that zones of altered bedrock on the rolling upland reflected deep weathering, local hydrothermal alteration and lithologic control. The slow pace of steep uphill climbs through deep roadcuts allowed recognition of soils buried between tills, stone lines that reflected latest Pleistocene periglacial conditions, as well as buried “red” soils in colluvium that suggested extended periods of landscape stability. Peter Birkeland observed with a careful eye coupled with a familiarity with prevailing geomorphic questions, and advanced our understanding of process and stratigraphic questions over many decades. Finally, he served as a role model for his former students by staying active physically and engaged mentally with grace and humility deep into his retirement years.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382265

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