Evolution of physiography and drainage in southern Yukon

Abstract

The physiography of southern Yukon is dominated by upland plateaux and plateau remnants that probably evolved in the Tertiary, culminating in a mature erosion surface about Miocene time. Variations in the elevation of this surface are thought to result from uneven uplift and faulting in the Late Miocene or Pliocene. The Tintina and Shakwak Trenches are young grabens superposed on the upland and the mountain ranges are youthful dissections of raised parts of the plateau.In the Miocene, water from central Yukon probably drained to the coast across the region occupied by the St. Elias and Coast Mountains. About the late Miocene, general uplift occurred and the St. Elias and Coast Mountains rose unevenly above interior parts of the Yukon. As a consequence, the drainage became entrenched. During deglaciation, ice in the St. Elias outlasted that in the interior and this forced derangements of the entrenched stream system. It was abandoned in favour of the less direct northwest drainage of today. The northwest drainage persists, but is unstable and in danger of capture by more vigorous streams that flow directly to the coast.La physiographic du sud du Yukon est dominee par les hauts plateaux et des vestiges de plateaux qui se sont probablement developpes au Tertiaire pour arriver a une surface d'erosion de maturite au Miocene. Les variations dans I'elevation de cette surface sont probablement le resultat du soulevement inegal et du faillage a la fin du Miocene ou au Pliocene. Les fosses de Tintina et de Shakwak sont de jeunes grabens superposes aux plateaux et les chaines de montagnes sont des dissections plus jeunes dans les parties soulevees du plateau.Au Miocene, I'eau provenant du centre du Yukon se drainait probablement vers la c6te a travers la region occupee par les monts Cbtiers et St-Elie. Vers la findu Miocene, un soulevement general s'est produit et les monts St-Elie et Cbtiers se sont eleves inegalement au-dessus des parties interieures du Yukon. Comme consequence, le drainage s'est retranche. Durant la deglaciation, la glace de St-Elie a persiste apres la fonte de celle de I'interieur et celaa provoque des derangements dans le systeme de cours d'eau retranches. Ce systeme a ete abandonne en faveur du drainage moins direct vers le nord-ouest qu'on observe aujourd'hui. Le drainage au nord-ouest persiste mais il est instable et en danger de capture par des cours d'eau plus vigoureux qui coulent directement vers la cBte.[Traduit par le journal]Can.

Characterizing large river history with shallow geophysics: Middle Yukon River, Yukon Territory and Alaska

“…Middle Yukon River drainage is generally northwest-trending, reflecting the structural grain of accreted terranes and large transcurrent faults that occupy the northern Cordillera of Yukon and adjacent Alaska (Tempelman-Kluit, 1980). Yukon River drainage begins in southwestern Yukon in the glacierized St. Elias Mountains and northwestern British Columbia (Fig.…”

“…Uplands of the Yukon-Tanana Terrane in western Yukon are generally below 1400 m, and the dissecting incised valleys have relief of up to 500 m. The Yukon Plateau is an uplifted erosional or planation surface produced from extensive subaerial exposure in the early-mid Tertiary (Tempelman-Kluit, 1980). Through the late Tertiary, a south-flowing paleoYukon River is hypothesized, with a drainage divide near the Alaska border, connecting the area north of the Tintina Fault zone with the Pacific Ocean (Tempelman-Kluit, 1980;Duk-Rodkin et al, 2001;Froese et al, 2001).…”

“…Through the late Tertiary, a south-flowing paleoYukon River is hypothesized, with a drainage divide near the Alaska border, connecting the area north of the Tintina Fault zone with the Pacific Ocean (Tempelman-Kluit, 1980;Duk-Rodkin et al, 2001;Froese et al, 2001). This drainage likely extended across the area presently occupied by the St. Elias and Coast mountains, and may have persisted through uplift of the southwestern Yukon ranges during the Pliocene (Tempelman-Kluit, 1980). The Yukon River would have been diverted to the northwest into central Alaska by the growth of late Cenozoic ice sheets by 2.6 Ma (Froese et al, 2000;Duk-Rodkin et al, 2001).…”

Comparative analysis of glacial and nival streamflow regimes with implications for lotic habitat quantity and fish species richness

“…Detailed inspection of fine-scale topographic maps reveals that individual catchment boundaries can locally be topographically extremely subtle in spite of the considerable overall relief in the region. The Icefield Ranges form a continental drainage divide, but this is a geologically very recent and possibly temporary development (Tempelman-Kluit, 1980; see also Bryan, 1972), and a number of rivers with headwaters in the continental interior penetrate this substantial but discontinuous topographic barrier to empty into the Pacific. One of the study rivers (Kluane; see below) may have reversed flow directions and switched continental drainages in the recent postglacial Holocene (Bostock, 1969), and at least two of the study rivers (Dezadeash and Alsek) have experienced substantial, repeated drainage obstructions due to periodic surges of the Lowell Glacier, which formed large glacier-dammed lakes within these catchments; the most recent full blockage may have occurred around 1900 (Clague and Rampton, 1982).…”

Permafrost, tectonics, and past and future regional climate change, Yukon and adjacent Northwest Territories

“…The Yukon Plateaus are remnants of a Tertiary erosion surface that was levelled between 45 and 15 Ma (Templeman-Kluit 1980). Rudiments of the present drainage network were defined by the end of the Miocene (Templeman-Kluit 1980), but the Early Pleistocene relief was likely much less than today (Mathews 1989).…”