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Reports a 1964-65 summer investigation of the north and central arms of this glacier with reference to surface ice deformation at a glacier confluence and its relation to optic-axis fabrics of the ice. The fabrics are concluded to be a result of synkinematic recrystallization, although the nature of the control of this recrystallization is not known.

During retreat of the Cassiar lobe of the Cordilleran ice sheet from the last glacial maximum there was a large stagnation or re-advance near what is now the north end of Lake Laberge (Lower Laberge) in the south central Yukon. This stagnation generated a large moraine that would come to act as a sediment dam for Glacial Lake Laberge. As the retreat of the ice front resumed a lake formed between the ice front to the south, and the sediment dam to the north. With the ice front continually drawing further south, combined with incision of an outlet flow into the sediment dam, the geomorphology of Glacial Lake Laberge constantly changed. Throughout the history of Glacial Lake Laberge there has been a gradual decline in the lake level largely controlled by incision into the sediment dam near Lower Laberge, as is indicated from sets of fluvial terraces above the current outlet river (the Yukon River). This gradual decline has produced several sets of preserved shorelines rising above the present lake level. By surveying the shape, location, and elevation of these shorelines and outwash terraces, in combination of all other applicable data sets, a detailed glacial retreat and alluvial history can be examined.

Previously unrecognized glacial erosional landforms (i.e. cirques, u-shaped troughs, truncated spurs and arêtes, in order of increasing doubt), and glacial depositional landforms (i.e. end moraine and possibly ground moraine) occur in the Fifty Mile Creek area, west of the pre-Reid Cordilleran glacial limit. The cirques and end moraine, representing the best evidence of glaciation, are similar to landforms in the adjacent Yukon-Tanana uplands of Alaska and formed during the Eagle glaciation (>40 ka, or Reid in age). Glaciation caused climate-controlled variations in runoff and cycles of aggradation and incision in the Fifty Mile Creek drainage. This resulted in the formation of upper- and lower-level terraces along Fifty Mile Creek and its tributaries. The terraces are composed of slightly muddy, sandy gravel of locally derived lithologies, and are fluvial in origin. Placer gold occurs along Fifty Mile Creek and several of its tributaries, as well as in the lower-level terraces. The upper-level terraces are potentially placer-gold bearing.

Llewellyn Glacier contributes glacial meltwater to runoff entering the Yukon River, which flows through the hydroelectric power dam in Whitehorse, Yukon. An examination of lateral moraine stratigraphy, and radiocarbon and dendrochronological dating of in situ and detrital subfossil wood provide a record of fluctuations of Llewellyn Glacier over the past two millennia. Our data indicate the north lobe advanced sometime between AD 260 and AD 505, and reached within 70 m of its Little Ice Age maximum limit as early as the 17th century. The main lobe advanced as early as AD 1035, possibly between the First Millennium and Little Ice Age advances of the last two millennia, when glaciers have traditionally been considered more restricted. Results provide new information on the timing and frequency of fluctuations of Llewellyn Glacier, and can be used to assist with modelling the future impacts of climate change on glacial meltwater contributions to rivers and hydroelectric security in Yukon.

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Ice accumulations in the Coast Mountains of southwestern Yukon and the Cassiar Mountains of south-central Yukon during the late Wisconsinan were responsible for glaciation of the Whitehorse area. Cirques in the Coast Mountains likely supported the first glaciers that advanced out of the mountain valleys ahead of the more distal Cassiar accumulation. Glacial maximum is characterized by topographically unconstrained ice flow trending northwesterly over most of the map area. Ice thickness over the city of Whitehorse exceeded 1350 m during full glacial conditions. Deglaciation is characterized by frontal retreat punctuated by periods of dynamic equilibrium and readvances. Differential retreat of the Cassiar and Coast Mountain ice lobes enabled the Cassiar lobe to penetrate, and at times readvance, up-gradient into Coast Mountain valleys. This pattern of deglaciation created ice dams and a series of proglacial lakes that submerged valleys under as much as 300 m of meltwater.

Late Wisconsinan McConnell glaciation (ca. 24-11 ka) occurred in four phases in the Pelly Mountains of southern Yukon. Phase 1 marked the onset of ice accumulation in cirques above 1524 m above sea level (a.s.l.). These local glaciers expanded and fed valley glaciers that extended into the surrounding lowlands (after 26.3 ka). At glacial maximum or phase 2, the development of ice-divides to the east and south of the Pelly Mountains permitted Cordilleran ice lobes to invade the lesser glaciated Pelly Mountains, which resulted in up-valley ice-flow. This ice-flow arrangement continued into early deglaciation (phase 3), a period characterized by re-advances of the invading ice lobes. Following retreat of the ice lobes from the Pelly Mountains, some local cirque glaciers above 1600 m a.s.l. resumed limited down-valley flow (phase 4). For drift prospecting purposes, the dominant glacial dispersion trajectory in these high relief areas is controlled by the last phases of ice-flow (either phase 3 or 4).

Four stages of ice-flow occurred in Howard’s Pass during the late Wisconsinan McConnell glaciation. The first stage is marked by ice growth from local cirques. During the second stage, an ice divide developed east of the Nahanni River, with ice flowing southwest across Howard’s Pass. Ice sheet growth continued during stage 3 and the ice divide migrated southwest into the Logan Mountains. At this time ice flowed northward across the study area. Stage 4 is marked by deglaciation and more topographically influenced ice-flow. This last phase of ice-flow is the most important for drift prospecting in the valley bottoms. Conversely, drift transport directions at higher elevation are likely remnant from earlier stages of ice-flow. A mobile-metal-ion survey over a known deposit returned promising results, supporting the potential of this geochemical technique in other drift-covered areas of Howard’s Pass.

Includes glacial limits, glacial deposits, ice-flow direction and descriptive notes on placer gold and glaciation in the Dawson area.