Pleistocene glaciation in the southern part of the North Cascade Range, Washington Stephen C. Porter 1976 Maddy Hummer, ESS 433, Nov

Introduction – Emphasis placed on describing the stratigraphic succession, on developing a chronology of glacier fluctuations, on examining the relationship of valley glaciers to the Puget Lobe of the Cordilleran Ice Sheet – The Cascades split Washington into two contrasting climactic regions Precipitation and vegetation

Stratigraphic Usage – Drift: sediments resulting from an ice advance Drift sheets have lithofacies of till, erratic stones, outwash, glacial-lacustrine sediments, and ice-contact stratified drift. Sediments originating during glaciations but not deposited directly by ice or associated meltwater are excluded from drift.

Criteria of Age – Time dependent Progressive change in degree from weathering, erosion, mass wasting, or extent of vegetation cover with increasing age of deposits – Independent of time Based largely on spatial relationships of physical characteristics of the drifts

Criteria of Age  Most widely applicable methods were weathering rinds, loess thickness, soil-profile characteristics, and moraine and terrace

Weathering Rinds  Clasts on Teanaway Basalt were measured for each drift  Rind measurements are inadequate to distinguish members because of overlap between members of the Kittitas Drift overlap, as well as in the Lakedale Drift

Loess Thickness  Max thickness varies systematically with the age of underlying drift for the Kittitas and Lakedale Drift – Range of 3.5 m on moraines and terraces of Swauk Prairie to only 0.7 m on those of Domerie Age

Soils Grain-size analysis, pH, percentage of magnetic minerals, and moist color – Curves of clay size emphasized pedogenic clay enrichent, but reflect variations in silt and clay content of loessial parent materials as well – PH = 5 – 7, limited value due to difficultly of interpretation – Percentage of magnetic materials was in hope that it would provide an index of weathering, but results were not signigicant – Gross color differences were useful in distinguishing soil-stratigraphic units: the younger soils commonly have yellowish-brown hues, the older soils have red hues

Moraine and Terrace Relationships Moraine spacing and distance from cirques is a crude comparison of moraine successions in adjacent valleys Direct correlations between valleys are possible by directly tracing outwash terraces that border the Yakima River, its tributaries, and back to moraines.

Upper Yakima River Drainage Basin – Largest in the Cascades – Valley glaciers merged together and formed confluent ice streams more than 40 km long and 400 m thick – Drift sheets spread out many kilometers – Most common landforms are end moraines and outwash terraces

Possible Pre-Thorp Drift Weathering rind of / Shorter advances because neither till nor terraces of pre-Thorp age were found at or beyond the Thorp and Swauk Prairie terminal moraines

Thorp Drift Oldest glacial sediments 65 km east of Cascade divide Horse Canyon and South Slope of Lookout Mountain – Soil: 2.5 m of dark reddish (5YR 3/4), stony, fissle till. Weathering rind avg: / Terrace surface maximum at 140 m above the Yakima River, North of Thorp Outwash is deeply oxidized

Kittitas Drift Composed of two members: – Swauk Prairie Member (Swauk Prairie and Thorp Prairie), and the Indian John Member

Swauk Prairie Member: Swauk Prairie Composed of six arcuate ridges of stony till regularly mantled with loess Moraine altitude of 750 m Weathering and erosion rates less than Thorp Drift Till is rounded pebbles and cobbles of Teanaway Basalt, sandstones of Roslyn and Swauk Formations

Swauk Prairie Member: Thorp Prairie Single arcuate ridge Crest altitude is 650 m, 165 m above the Yakima River Till is stony, high percent of angular boulders of Yakima Basalt and very few Teanaway Basalt clasts Weathering rind avg: /- 0.11

Indian John Member Formed during major re-advance after the Swauk interval but during the same glaciation Weathering characteristics are nearly indistinguishable Weathering rind avg: / Fluvial sediments are exposed Poorly sorted boulder-cobble gravel, layers of finer gravel and sand

Indian John Member Had three low end moraines Lateral moraine traced for 10 km westward means that the glacier was confined to the main valley During the glacier’s retreat a lake formed. – There is bluish lacustrine sediments – Larger than the current lakes in the area

Post-Kittitas Soil Separates the Kittitas and Lakedale drift sheets Textural B horizon, cm thick with clay enrichment, brown color (7.5 YR 4/4), angular to prismatic clay skins Contrast to post-Lakedale soil which lacks clay enrichment and is dark brown (10 YR 4/3) color B horizon) Advance between Indian John and Bullfrog Drifts – almost identical to the post-Kittitas soil at Swauk Prairie

Lakedale Drift Subdivision determined by the outwash terraces Four members: – Bullfrog – Ronald – Domerie – Hyak

Bullfrog Member Has two crests; two tills exposed in the two terminal loops implying two distinct advances Lake sediments behind the outer Bullfrog moraine and in the inner moraine – inner lake went up-valley for 6 km Weathering rind avg: /- 0.12

Ronald Member 3 loops Northwest, and above, of Bullfrog due to a halt or re-advance Another moraine West of the Ronald moraine complex was built during a re-advance – Proglacial lake sediments were deformed by a re- advance of the glacier following its retreat from the Ronald moraine

Domerie Member Prominent moraine systems surrounded the lower ends of Kachess Lake, Swamp Lake, and Keechelus Lake

Hyak Member Youngest Lakedale Drift Small, residual valley and cirque glaciers in the area Moraines occur through a distance of 3.2 km between Hyak and the pass Moraines consist of crudely stratified flowtill, evenly laminated lacustrine sediments and fluvial sand and gravel – Stagnant and melted out differentially but ridges are sharp crested indicating the glacier terminus remained actived

Holocene Sediments Looking at tephra in the moraines provides relative ages – Moraines without tephra are younger than 450 years old

Post-Lakedale Sediments Weakly developed compared to post-Kittitas soil Some Lakedale members have a weak color-B horizon (10YR 4/3)

Snoqualmie River Drainage Basin: Drift of the Puget Lobe Sublobes of the glacier drifted into the lower ends of the west-draining Cascade valleys, blocking streams and depositing thick drift Snoqualmie embayment formed where the valleys of the South and the Middle Forks of the Snoqualmie River and the Cedar River met the Puget Lowland It is suggested by Mackin (1941) that the valley glaciers had retreated from their maximum stands prior to the advance of the Puget Lobe

Drift of Pre-Vashon Age Laminated lake sediments containing peaty organic matter and wood fragments having a radiocarbon age of >50,000 years (UW-243) were exposed near the bottom of South Fork moraine embankment They pre-date the Vashon drift which has an age between 15,000 and 13,500 years (Mullineaux and others, 1965) Lake sediments date to pre-Fraser ponding in the Snoqualmie Embayment

Vashon Drift High massive delta moraine complex that crosses the lower ends of the principal valleys Coarse boulder and cobble gravel into well- sorted gravel and sand up-valley and finally turns into evenly laminated lacustrine silt and clay about 90 m thick

Lakedale Drift Valley glacier advanced up to a point within 4 km of the Snoqualmie Embayment prior to the Puget Lobe’s maximum. – Mackin (1941) found alpine till beneath rubbly rock that was overlain by Vashon lake sediments – Terminal deposits were buried so extent is unknown

Lakedale Drift Bandera has 5 nested moraines which correlates with the approximate position of the South Fork glacier – Reconstructed profile of the South Fork glacier lies above the Hyak Drift limit, below the Ronald and Bullfrog ice in Keechelus valley, but coincides closely with the Domerie ice limit This means that the outermost Vashon Drift in the Puget Lowland and the Domerie Member are approximately the same age

Chronology and Regional Correlations

Take Away Used weathering rinds, moraines, terraces, soils and loess to determine differences between glacial drifts There were 7 major Pleistocene glaciers between North Bend and Ellensburg, 3 Drifts We can correlate information about the Yakima glaciers with the Puget Lobe to determine ages and time of advance and retreat