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Lake Pondilla

USGS Topo Sheet: Port Townsend North

Geographic coordinates: 48°13.57' N, 122°35.57' W

Paleoseismic record: Based very limited reconnaissance, this site does not appear likely to have recorded paleoseismic events. If future work shows that tsunamis on this coast have exceeded 8 masl (meters above sea level), a more thorough coring study of the lake and swampy area south of it should be completed.

Setting: Lake Pondilla occupies a small kettle about 400 m north northwest of Pt. Partridge, the westernmost point of land on Whidbey Island. About 200 m southwest of the lake, a saddle separates a small swampy valley, which drains into the lake, from the sea. The saddle is probably composed of sandy silt drift and is 4.8 m above the crest of a sandy, log-filled storm berm at the back of the beach to the west. The lowest point on the saddle is probably about 7 masl; Lake Pondilla and the swampy valley are at least 3 m lower than the saddle. We briefly explored the site to evaluate its potential for recording and preserving tsunami deposits.

Stratigraphic description: Gouge coring (2.5-cm-diameter) in the small swampy valley directly east of the saddle (20-30 m wide) showed no obvious evidence of tsunami deposits. Ten <1.8-m cores spaced east-west about 60-75 m from the east edge of the asphalt road (in the center of the curve in the road) showed 0.3-1.5 m of peat sharply overlying sandy silt. A typical core showed:

    0-83 cm fibrous bog peat (Th2-34, Dl+)

    83-122 cm woody humified bog peat (Th33, Dl1)

    122-147 cm humified bog peat (Th24, Dl+, Ga tr)

    147-168 cm very fine sandy silt (As2, Ga2, Ag+, Dl+).

The peat is thinner on the north and west edges of the valley and thickest in the middle. In one core in the middle of the valley, a 2-cm-thick zone within the peat at 45 cm contained about 2-5% sand. A few angular pebbles were found at the base of the peat in another core.

Paleontology/Paleoecology: No paleontologic work was completed. Diatom analyses would be useful in cores from the small swampy valley, if further work is attempted.

Geologic interpretation: The swampy valley is only a few tens of meters landward of the lowest point of land that provides marine access to Lake Pondilla. Thick peat that is at least a few hundred and perhaps a few thousand years old shows no signs of beach sand or other marine sediment or fossils. Sand and beach debris would be expected to have been deposited in the valley if tsunamis had overtopped the saddle and flowed through the valley and into the lake. The lack of marine material in the peat suggests that tsunamis on the west coast of Whidbey Island have not greatly exceeded the elevation of the saddle since the peat began to form.

Date of last work at site: September 1997

Status of work: No additional work is planned. Lake Pondilla is in Fort Ebey State Park; fieldwork within the park boundaries requires a state permit that might take 1-2 months to obtain.

Published information on this site: None

Investigators: A. Nelson, H. Kelsey

Please use the following format in citing information from this page:

Nelson, A.R., Kelsey, H.M., Lake Pondilla, in Bucknam, R.C., compiler, 1999, Atlas of reconnaissance data from paleoseismic studies in the Puget Sound region, Washington: U.S. Geological Survey Web Page, http://earthquake.usgs.gov/regional/pacnw/paleo/atlas.html.

This URL is: http://earthquake.usgs.gov/regional/pacnw/paleo/reports/lpondilla.htm
Modified July 29, 2002 by Susan Rhea