BOOTH’S PAPERS Channel networks carved by subglacial water: Observations and reconstruction in the eastern Puget Lowland of Washington & Glaciofluvial infilling and scour of the Puget Lowland, Washington, during ice-sheet glaciation Andrew Kimn ESS 433

Channel Ways & Cordilleran Ice Sheet into Puget Lowland The Cordilleran Ice Sheet expanded 6x Channel Ways – Absent in Interior Forms dendritic or anastomosing networks Prominent across the west trending bedrock spurs of the Cascade Range that lie transverse to the ice-flow direction Origin Subglacial water is the most plausible agent of channelway formation (Beneath the Puget Lobe in Particular) Anastomosis - is the reconnection of two streams that previously branched out, such as blood vessels or leaf veins

Static Ice Analysis H = Total head z = elevation head h = height above a chosen ‘datum’ such as sea level Pi = ice density (900 kg*m -3 ) Pw = water density (1000 kg*m -3 ) Water flow is influenced by ice surface & bed topography Tends to follow ice-slope direction and flows up and down bed topography

Static Ice Analysis with ‘Sliding Ice’ p = Dynamic Pressure Component n = effective ice viscosity U = sliding velocity Ax = amplitude hx = wave number (x appears because it is sliding) Basal ice motion over a nonplanar bed surface, such as many drumlins, increases the pressure head on stoss slopes (stoss – i.e. steeper side of drumlin) and reduces it on lee slopes (lee – i.e. tail end of a drumlin)

Eastern Puget Lowland Reconstruction: 2 distinct categories of flow paths revealed 1. Crude dendritic network trending SE 2. Single submarginal valley near the eastern boundary of ice sheet

Glaciofluvial Infilling Great Lowland Fill 1. Proglacial rivers carried fluvial sediment away from front of the ice 2. Sediment filling was likely 1. Basin became a closed depression once the ice advanced south past the entrance of the Strait of Juan de Fuca 2. Surface graded to the basin outlet in the southern Puget Lowland (took roughly years to fill) 3. Deposition was complete in P.L. before total ice coverage

Mapping Support Geological mapping supports that elevation across P.L. is determined by thickness of Vashon advance outwash Outwash and converging basil till contact is unknown

Glaciofluvial Erosion of the Lowland Troughs Trough formation was after the deposition of the great Lowland fill It is thought that 1000 m thick of ice occupied area of Puget Lowland as whole eroded (1000 km 3 ) 75% is by trough erosion

Average sediment transport rate was about 0.2 km 3 /yr, so total would have take about 5000 yrs To note, the rate of ice sheet advance may be limited by rates of sediment production & deposition