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.

The late Wisconsinan McConnell glaciation of the Big Salmon Range in the Pelly Mountains consisted of a four-phase ice-flow history. Phase 1 ice-flow consisted of local alpine glaciers advancing to the mountain front. During phase 2, or glacial maximum, the Cassiar lobe of the Cordilleran ice sheet advanced to the northwest and overtopped the range. Retreat of the Cassiar lobe during phase 3 of the glaciation resulted in ponding of meltwater in eastern drainage basins. The meltwater spilled over into western basins and caused significant erosion of surficial sediments. Phase 4 of the glaciation is marked by a limited late-glacial readvance of local alpine glaciers. This glacial history has several important implications for mineral and placer exploration in the area.

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.

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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Preliminary investigation of surficial geology in northern Kluane Range has resulted in new interpretations of Pleistocene ice cover including extensive unglaciated terrain and restricted glaciation during the Last Glacial Maximum. Two glacial limits are identified: a higher limit recording the most extensive glaciation of the area; and a lower limit that records younger, less extensive glaciation. This paper describes Pleistocene limits of the Donjek Glacier and the distribution of surficial materials in the upper Quill, Maple, and Wade creek drainages. The source and transport mechanism of surface materials has particular significance for surficial geochemistry sampling programs and implications for mineral exploration are addressed.

Uplands in west-central Yukon supported alpine ice centres during the pre-Reid glaciations (Early Pleistocene). Subdued cirque forms are thought to be glacial cirques that have undergone degradation by nivation. The paleo-equilibrium line altitude (ELA) dropped as low as 1054 ± 96 m in the Crag Mountain upland (CMU). A pre-Reid age for the CMU cirques is based upon the presence of an Early-Middle Pleistocene paleosol in a moraine feature. Cirques in the Ogilvie Mountains provide proxy ELAs for the Reid (mean 1391 ± 132 m) and McConnell (mean 1488 ± 103 m) glaciations. Cirque glaciers did not form in CMU and most of Dawson Range during these later glaciations due to a decrease in precipitation. It is suggested that the progressive marginality of cirque glaciation through the Middle and Late Pleistocene may be related to the progressive enlargement of precipitation-diverting continental ice sheets east of the Cordillera.

A comprehensive stable isotope study of basal ice and debris layers in two Yukon surging glaciers suggests an isotopically variable basal freezing cycle. Trapridge and Backe glaciers, St. Elias Range, Yukon, have parallel basal debris layers that extend for hundreds of metres along marginal ice faces and in meltwater tunnels. Both glaciers are subpolar surging glaciers that surge on a cycle of 40-50 years. They are approximately 5 km long and 1 km wide with a lower ablation zone that is frozen to the bed and an upper accumulation zone that has basal ice at the pressure melting temperature.

Glacial history reconstructions and geomorphic mapping in the North McQuesten River, Dublin Gulch, and Keno Hill map areas indicate a succession of less extensive glaciations. From oldest to youngest, the main glacial episodes are the pre-Reid (multiple glacial episodes), Reid and McConnell glaciations. The surficial geology of the study area is dominated by deposits of the Reid and McConnell glaciations. Pre-Reid glacial deposits are mostly confined to infrequent erratics on plateau areas above the Reid glacial limit. Glacial limit mapping indicates that ice flow patterns were similar in both the Reid and McConnell glaciations. Valleys aligned parallel with glacial ice flow are broad and U-shaped with significant glacial deposits in valley bottoms. In contrast, valleys aligned transverse to glacial ice flow are narrower and have a more V-shaped morphology. This relationship appears to be a controlling factor on the distribution of placers in the study area. Numerous drainages were analyzed for their placer potential in each of the three map areas. Their potential was based on geomorphic evaluations, glacial history, geochemistry, bedrock geology, and historic records. A concentration of potential placer creeks were identified in the Keno Hill/Mayo Lake area. Fewer prospective creeks were identified in the Dublin Gulch and North McQuesten River map areas.

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.