Bruce E. Broster

Multiphase flow of the late Wisconsinan Cordilleran ice sheet in western Canada

In central British Columbia, ice flow during the late Wisconsinan Fraser glaciation (ca. 25–10 ka) occurred in three phases. The ice expansion phase occurred during an extended period when glaciers flowed westward to the Pacific Ocean and east-southeastward onto the Nechako Plateau from ice centers in the Skeena, Hazelton, Coast, and Omineca Mountains. Initially, glacier flow was confined by topography along major valleys, but eventually piedmont and montane glaciers coalesced to form an integrated glacier system, the Cordilleran ice sheet. In the maximum phase, a Cordilleran ice divide developed over the Nechako Plateau to 300 km inland from the Pacific coast. At this time, the surface of the ice sheet extended well above 2500 m above sea level, and flowed westward over the Skeena, Hazelton, and Coast Mountains onto the continental shelf, and eastward across the Rocky Mountains into Alberta. In the late glacial phase, a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys, and restricted accumulation centers to high mountains. Discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness. Ice centers probably shifted in response to climate, irregular growth in the ice sheet, rapid calving, ice streaming, and drainage of proglacial and subglacial water bodies. Crosscutting ice-flow indicators and preservation of early (valley parallel) flow features in areas exposed to later (cross-valley) glacier erosion indicate that the ice expansion phase was the most erosive and protracted event.

Dynamic Glacigenic Deformation of Near-Surface Metamorphic Bedrock: Heath Steele Mines, New Brunswick

Near-surface metamorphic bedrock at Heath Steele Mines, New Brunswick, was fractured to depths of at least 35 m and possibly as deep as 120 m, during two stages of glacier overriding. Fracturing was accompanied by crack-filling of sediment-laden melt waters, increased pore pressures, freezing, and joint expansion. The upper few meters of the bedrock surface were extensively brecciated and folded. Brecciated bedrock fragments were reoriented as passive strain markers of interstitial ice deformed by subglacial shear. Dynamic glacigenic deformation is distinguished from older structures by: (1) structural associations with direction of glacial movement; (2) fracture infillings of distally derived and striated material; (3) iron-staining along open fractures; (4) near-surface strain partitioning of deformation, and (5) absence of axial plane foliations in fold structures.

A multidisciplinary assessment of postglacial seismic disturbance: Miramichi area, New Brunswick, Canada

Abstract Examination of deformed alluvial sediments, archaeological projectile points and historical seismicity formed the basis for an assessment of paleoseismicity at the Oxbow site in the Miramichi region of New Brunswick, Canada. Deformed masses of layered sediment, containing discontinuous and folded layering, were interpreted to have been caused by seismically-induced liquefaction of unfrozen sediment. Artifacts and radiocarbon dating provided a chronological record extending over 2500 years and enabled relative dating of deformation of the sediments to between the 1700s and early 1900s. Results supported the inference that the region is subject to repeated ground disturbance from periodic earthquakes of magnitude 5 or greater.

A site selection case study using terrain analysis in conjunction with an evaluation matrix

Abstract Air photo interpretation (API) has long been recognized as a fundamental procedure for classifying surficial (superficial) materials in the reconnaissance stage of site evaluation. The results from an API study can help with the rapid assessment of the relative suitability of sites for development and hence reduce costly field work. This paper presents a case history which uses the comprehensive ELUC terrain classification system and API to define the geological framework for seven potential industrial sites. Prior to field investigations the sites were ranked for their suitability using an evaluation matrix. Engineering factors were subjectively quantified relative to geotechnical considerations and entered in the evaluation matrix. This enabled sites to be ranked so that subsequent ground exploration could be concentrated on the most suitable sites. The successful application of the method suggests that it can be used elsewhere as a cost-effective procedure for engineering terrain assessment in the process of site selection.

Geomorphology: A Canadian Perspective, Second Edition(Alan S. Trenhaile)

Alan Trenhailes Geomorphology: A Canadian Perspective (2004) is the improved second edition of a popular Canadian text on geomorphology. As the title states, the authors emphasis is on geomorphic processes that are most prevalent in Canada, but it also includes intermittent references to other examples. Although the physical processes covered are applicable to study in temperate and polar environments in other parts of the world, the book is intended primarily for use by Canadian undergraduate students. A major strength of the book is the inclusion of several formulae on sediment processes that are beneficial to an environmental geomorphologist. For the engineer or environmental scientist working in Canada, the book provides an overview of general geology and surficial processes most relevant to the Canadian landscape. The first chapter introduces the reader to the evolving study of geomorphology and basic sedimentary principles and lays the foundation for later discussions on geologic quantification of sedimentary processes. This chapter is useful reading for most professionals involved in the assessment of the Earths surface. In …