Abstract The Middle Fork Nooksack River drains the southwestern slopes of the active Mount Baker stratovolcano in northwest Washington State. The river enters Bellingham Bay at a growing delta 98 km to the west. Various types of debris flows have descended the river, generated by volcano collapse or eruption (lahars), glacial outburst floods, and moraine landslides. Initial deposition of sediment during debris flows occurs on the order of minutes to a few hours. Long-lasting, down-valley transport of sediment, all the way to the delta, occurs over a period of decades, and affects fish habitat, flood risk, gravel mining, and drinking water. Holocene lahars and large debris flows (>10 6 m 3 ) have left recognizable deposits in the Middle Fork Nooksack valley. A debris flow in 2013 resulting from a landslide in a Little Ice Age moraine had an estimated volume of 100,000 m 3 , yet affected turbidity for the entire length of the river, and produced a slug of sediment that is currently being reworked and remobilized in the river system. Deposits of smaller-volume debris flows, deposited as terraces in the upper valley, may be entirely eroded within a few years. Consequently, the geologic record of small debris flows such as those that occurred in 2013 is probably very fragmentary. Small debris flows may still have significant impacts on hydrology, biology, and human uses of rivers downstream. Impacts include the addition of waves of fine sediment to stream loads, scouring or burying salmon-spawning gravels, forcing unplanned and sudden closure of municipal water intakes, damaging or destroying trail crossings, extending river deltas into estuaries, and adding to silting of harbors near river mouths.

Abstract The Nooksack River Basin is situated in the steep western slopes of the North Cascade Mountains and low glacial plains of northwest Washington State. The basin drains west from the north and west sides of volcanically active Mount Baker and meets the sea at Bellingham Bay near the southern end of the Strait of Georgia. The dramatic topographic relief of the region is the result of tectonic activity along the Cascadia Subduction Zone. Pleistocene continental and alpine glaciations sculpted and scoured the region, modifying topography and mantling many areas with deposits of tills, outwash and glaciomarine drift. The Holocene saw the retreat of glaciers, rebounding of land, and the peopling of North America with indigenous cultures and then with Euro-American settlement. The Nooksack Basin has had a long history of cultural occupation as it provided both a transportation corridor and a prolific resource area. Although geomorphologically quiescent since Euro-American settlement, the landscape of the Nooksack Valley has experienced numerous landscape-altering events during the Holocene that very likely impacted, if not dramatically altered, the cultures that were present there. The purpose of this field trip is to show evidence for some Holocene geologic events and to contemplate human culture amidst this lively landscape.