Peter G. Johnson

Mass Movement of Ablation Complexes and Their Relationship to Rock Glaciers

The wide range of forms which have been identified as rock glaciers are examined. It is proposed from field evidence in the southwest Yukon Territory and from a survey of the literature that the forms should be investigated according to their processes of movement rather than their morphological form. Various distinct processes are discussed which depend on the origin of the ice responsible for the movement and the nature of the surficial materials in which the movement has taken place. It is concluded that morphological expressions of flow are created by widely differing processes and that the use of traditional terminology tends to obscure these differences.

GLACIER-ROCK GLACIER TRANSITION IN THE SOUTHWEST YUKON TERRITORY, CANADA

In the southwest Yukon Territory rock glaciers of both the glacier debris system type and the talus type are common. In addition there are many examples of the transition between glaciers and the glacier-ice-cored type of feature. The glacier-ice-cored forms characteristically develop within or emanate from cirque basins where the formation of a complete debris cover of the glacier surface has been possible. Flow of these rock glaciers is due to periods of glacier advance with some secondary deformation of the ice under the debris cover after the retreat of the glacier. This secondary deformation accounts for movements measured at the present day. Comparisons are made among an ice-cored moraine system, a transitional form, and a large glacier-ice-cored rock glacier. The different flow lobes of the

Rock Glaciers of the Dalton Range, Kluane Ranges, South-West Yukon Territory, Canada

Glaciated valleys of the Dalton Range in the south-west Yukon Territory are dominated by rock glaciers identified as glacier ice-cored debris systems. The two rock glaciers studied have different amounts of deformation at present, resulting from post-formation mechanics. The primary formation of lobes of the rock glaciers resulted from periods of glacier activity in the Neoglacial, although older lobes, probably late Pleistocene in age, occur below the Neoglacial lobes. The hydrological systems of the rock glaciers have played a major role in the post-formation deformation of the land forms and the present drainage system is entirely sub-surface. The explanation for the extensive occurrence of rock glaciers in the Dalton Range is lithological as a result of the high susceptibility of the Upper Jurassic/ Lower Cretaceous sediments to frost action and glacier erosion .

Ice Cored Moraine Formation and Degradation, Donjek Glacier, Yukon Territory, Canada

The ice core of moraines at the terminus of the Donjek glacier is primarily composed of glacier ice and not snow bank ice. The widespread occurence of these ice cored moraines in the area is the result of two main processes, one a shear-push mechanism of buried stagnant ice and the other due to ablation and fluvial deposits accumulating on a stagnant ice wedge being pushed in front of the presently surging glacier. Degradation of these moraines is due to five main processes, all of which are directly related to the occurence of the ice

ROCK GLACIERS. A CASE FOR A CHANGE IN NOMENCLATURE

The connotation of the term rock glacier, has been one of a common origin form but it is increasingly appar- ent that we are studying a range of landforms which, with the exception of the glacier debris system type, have no relation- ship with glaciers. The approach to rock glaciers as a unique form is re-evaluated in the light of the vast numbers which occur in the southwest Yukon. The implications are that they are the norm not the unusual in the development of the progla- cial landscape and that correctly identified will provide new evidence for post glaciation landscape evolution.

The Development of an Ice-dammed Lake: The Contemporary and Older Sedimentary Record

An ice-dammed lake on the northern margin of the Kaskawulsh Glacier in the St. Elias Mountains has drained annually for at least 30 to 40 yr. Input to the lake is from three glacierized sub-basins and from the margin of the Kaskawulsh Glacier. The deltas of the streams from each of the sub-basins are constructed and destroyed in each filling and draining cycle. There is little sediment accumulation in the lake basin due to subglacial drainage of the high density underflow input through most of the filling sequence. Older lacustrine sediments and deltas demonstrate previous higher level lakes, which were semipermanent, during the early phases of deglaciation after the maximum of the Little Ice Age. One of the sub-basin glaciers is a surging glacier, and a sequence of old deltas indicate that the location of the discharge stream has changed during each surge. It is hypothesized that continuing downwasting of the Kaskawulsh Glacier will eventually remove the conditions for damming.

Stagnant glacier ice, St. Elias mountains, Yukon

The extensive occurrence of glacier ice cores to landforms and deposits of the Neoglacial and Little Ice Age periods in the St. Elias Mountains of the southwest Yukon is described. These glacier ice cores were produced during active glaciation and have been preserved, in locations such as the Donjek Glacier moraine, for over 500 years. Incorporation of ice in landforms and deposits occurs during glacier surges, glacier advance or glacier backwasting as well as during stagnation of the glacier. The primary terrain ranges from sequences of moraines, providing a detailed record of glacier fluctuations, to ice contact landforms. The degradation of the ice-cored terrain is controlled by hydrological and glaciological processes. which expose the ice core, rather than by melt beneath the surficial materials.

Spatial and temporal variability of ice-dammed lake sediments in alpine environments

Abstract The stratigraphic record of ice-dammed lakes is the product of a combination of daily, intraseasonal, seasonal and interseasonal fluctuations in sediment input combined with periods of drawdown or drainage of the lake. Sedimentation may take place on an ice-cored bed which produces deformation structures on melting and eventually results in limited preservation during and after deglaciation. The sediments of the contemporary and older ice-dammed lakes in the Kaskawulsh and Dusty Glacier basins of the southwest Yukon reflect a number of hydrological regimes and lake histories, and also demonstrate the complexity of the sedimentary environment. The Kaskawulsh Glacier lake evolved from being semi-permanent at the start of deglaciation from the Little Ice Age maximum to annually draining at present. The Dusty Glacier Lake was impounded by glacier surges and had a duration of only a few years after each surge. A model of the effects of variations in sediment source, contrasting hydrological regimes and geomorphological events on sediment accumulation illustrates how spatial and temporal variability is the predominant characteristic of the sediments.

VLF surface-impedance measurements for ice-depth mapping : an assessment of some commonly encountered interference effects

The effects on very low-frequency surface-impedance measurements of lateral variations commonly found in ice environments have been measured and modelled numerically using the quasi-static two-dimensional boundary-element method. Results indicate that surface-impedance measurements made in the vicinity of crevasses oriented perpendicular to the plane of incidence, and those made in the vicinity of moraines and melt streams, can all show significant changes to the measured apparent resistivity. It is. therefore, misleading to use such measurements in the interpretation of ice depth.

Proglacial and Paraglacial Fluvial and Lacustrine Environments in Transition

Geomorphology has two interlocking paradigms; the first is a process paradigm where there is a hierarchy of knowledge through the physics of a medium, the mechanics of process, to the landscape form; the second is a temporal paradigm from the history of the landscape, to the present condition, and with a prediction capacity. These are central to concepts of landscape transitions and landform assemblages. The paper explores landscape transitions occurring in proglacial and paraglacial environments based on the horizontal link of sediment transfer rather than on the traditional vertical division into glaciology, hydrology and periglacial geomorphology. In glacierized mountain areas the superimposition of transitions at different scales can readily be demonstrated within the regional landscape. Transitions may occur slowly, rapidly or instantaneously but their frequency of change will vary depending on the underlying cause of the transition. The concept of landform assemblages should integrate the ideas of process activity at different spatial, quantitative and temporal scales. Landform assemblages are therefore infmitely variable. The ways in which the concepts of transition and landform assemblages influence geomorphological interpretation is illustrated by reference to the glacierized environments of the southwest Yukon.