Geomorphic map of western Whatcom County, Washington

Dori J. Kovanen; Ralph A. Haugerud; Don J. Easterbrook

doi:10.3133/sim3406

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Geomorphic map of western Whatcom County, Washington

Dori J. Kovanen·Ralph A. Haugerud·Don J. Easterbrook

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Abstract

Western Whatcom County has a rich history of glaciation, sea-level change, fluvial erosion and deposition, landsliding, nearby volcanic activity, and human landscape modification. This lidar-derived geomorphic map interprets this history from the form and position of the Earth’s surface. The geomorphic record is broken into nine phases, beginning with the peak of the Vashon stade of the Fraser glaciation of Armstrong and others (1965) (phase 1), shortly after 16,000 years ago. The Cordilleran ice sheet was ≥1.6 km thick in the Bellingham area. Glacial lineations on high ground demonstrate that ice flow was from north to south. Storage of water in ice sheets at this time resulted in global sea level ~120 m lower than at present. The weight of the ice sheet depressed the land so that local relative sea level was at least 150 m higher than at present. As the ice sheet melted and thinned, it floated, broke up, and was replaced by salt water. The margin of the ice sheet—or at least its grounding line—retreated to the northeast of the map area during or before phase 2. Marine deposition, currents, and waves smoothed earlier-formed surfaces in the western part of the map area. Global sea level rose (because of melting of continental ice sheets), but the Fraser Lowland rose even faster (due to glacio-isostatic rebound following the loss of ice-sheet load), and thus local relative sea level fell. The Cordilleran ice sheet readvanced during the Sumas stade of Armstrong and others (1965). Oldest Sumas moraines formed when relative sea level at Bellingham was ~55 m (phase 3). Younger moraines formed when relative sea level at Bellingham was ~25 m (phase 4). The amount of Sumas ice retreat and readvance between these times is unknown. Younger Sumas events are marked by local moraines, progressive isostatic rebound and lowering of relative sea level, and changes in the flow of ice-marginal water. During phase 5, the southeast margin of the ice sheet advanced, perhaps because capture of ice-marginal drainage by the Samish River (east and south of the map area) meant the ice sheet was no longer trimmed by high-discharge flow along Squalicum channel. Farther west and north, the ice margin retreated between phases 4 and 5. Phases 6 through 9 may mark stillstands during further ice retreat. There were glacial outburst floods (jökulhlaups) during phases 7 and 8, and perhaps during phase 5. When Sumas ice left the area, perhaps about 11,500 years ago, the Nooksack River appears to have discharged northeast through Sumas Valley to the Fraser River. Details of the switch to its modern course are speculative, but archaeological and sediment-supply arguments suggest that the modern Nooksack River delta south of Ferndale formed within the past 5,000 years. The foothills of the North Cascades are decorated with abundant post-glacial deep-seated landslides. Anomalously high late Holocene beaches are found at Birch Bay, Neptune Beach, perhaps at Maple Beach on the east side of Point Roberts, and perhaps at the northwest corner of the Lummi Peninsula. These beaches may have been uplifted by earthquakes that did not rupture the surface. The low-relief landscape shaped by the Cordilleran ice sheet, along with fluvial infilling of low areas, resulted in abundant wetland, at least 70 percent of which has been diked and (or) drained to control flooding and facilitate farming.

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Source-reported bounding extent: 48.6169° to 49.0156° latitude; -123.1185° to -122.239° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Dori J. Kovanen, Ralph A. Haugerud, Don J. Easterbrook. 2020-08-10. Geomorphic map of western Whatcom County, Washington. https://doi.org/10.3133/sim3406

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