10-19-2013 Kathy Troost: Jökulhlaups

About the Field Trip

Jökulhlaups from Glacial Lake Puyallup, Pierce County, WA

Kathy Troost will present a lecture for the Jefferson Land Trust’s Geology Group entitled Jökulhlaupsfrom Glacial Lake Puyallup, Pierce County, WA.

For decades, geologists thought that normal surface flooding caused the surface channels and cobble deposits in Pierce County. However, these deposits are the result of repeated jökulhlaups (glacial outbursts) from Glacial Lake Puyallup during the retreat of the Vashon Ice Sheet about 13,500 years ago.

(Photo from https://commons.wikimedia.
org/w/index.php?curid=676643)

The affected landscape shows evidence of large outburst floods, such as kettle lakes from the grounding of large ice blocks, large-scale bed forms, waning-flow deposits with bogs, and thick deltas at the coast. As such the floods have shaped much of the landscape in Pierce County.

About the Speaker

Kathy Troost is a Licensed Geologist with 34 years of experience in geological research and investigations focused on the Pacific Northwest. Kathy has published many geological maps and papers about Quaternary geology and deposits. She teaches at the University of Washington in Seattle, has her own consulting company, is currently the President of the Northwest Geological Society, and will complete her doctorate at UW later this year.