- Email: [email protected]
Urban and Quaternary geology, New Zealand and eastern Australia
Quaternary International 103 (2003) 1–2
Editorial
Urban and Quaternary geology, New Zealand and eastern Australia Urban environments have become home to the majority of people on Earth at the beginning of the 21st century. In nations such as New Zealand and Australia, urban communities contain more than 75% of the population. Resource consumption by urban residents generally exceeds that of rural residents on a per capita basis. Each urban resident of New Zealand and Australia utilizes (at minimum) approximately 100 times the resources used by a rural resident of an underdeveloped nation. Thus, the expenditure of resources by the 1 billion urban dwellers in developed countries is approximately equivalent to that expected from a worldwide rural population of 100 billion. Increasingly, Quaternarists are called upon for investigations in urban environments, lending their expertise and chronological perspective to studies of natural hazards, waste disposal, water supply management, environmental pollution, and town planning. Our perspective, focusing on hominid–environment interactions throughout the Quaternary, provides us with the ability to make valuable contributions to life in urban centres. The multi-disciplinary approach endemic to Quaternary research is particularly suited to study of urban environments in the 21st century. Natural scientists have, as a group, preferred to focus on ‘natural’ environments, both as researchers and educators. Geological field trips may leave town as rapidly as possible; it’s not a ‘real’ field trip until the first gravel road is reached. On some geological maps, the urban areas are left blank, unmapped. Although geologists studying pre-Quaternary materials can discount human influences, this option is not viable for Quaternary geoscientists. Urban Geology has traditionally involved mapping and assessment of the distribution of Quaternary deposits and pre-Quaternary outcrops from the perspective of construction and hazard mitigation. Less concern is given to the linkage between climate (whether ‘natural’, or as it has varied and changed since city foundation) and ongoing geomorphic processes. Although this manifestation of Urban Geology is a valuable asset to Engineering Geology, additional approaches are possible. Relatively few urban geological studies consider the overall influence that Quaternary sediments and landforms have on a particular community, concentrating instead on geotechnical analysis at individual sites.
The papers presented in this volume investigate six communities in New Zealand (Auckland, Dunedin) and eastern Australia (Sydney, Toowoomba, Cairns, and Darwin). Edbrooke et al. investigated Auckland, the largest urban area in New Zealand. Auckland is marked by subdued rolling hills formed on weathered Mesozoic and Early Miocene sedimentary rocks, with many distinctive small volcanic cones. Terrestrial Quaternary sediments crop out in lowland areas and locally interfinger with and are overlain by Quaternary basalts. Geological hazards include slope instability, the threat of renewed eruption within the Auckland Volcanic Field, and the growing recognition of the potential effects of ash deposits from distant volcanic centres. Hazards related to seismic activity are also present. Recent recognition of active faulting close to the urban area has changed the perception of seismic risk. Glassey et al. investigated Dunedin, located on the remains of a Miocene volcanic eruptive centre underlain by Tertiary Late Cretaceous sediments. The geology and topography pose a number of geological hazards, including landslide, mine subsidence, ground-shaking amplification and liquefaction, coastal erosion and tsunami activity. A number of research, policy and planning initiatives have been undertaken to assess and mitigate the effects of these hazards, involving development of a GIS-based Hazard Information System. The Dunedin district plan includes policies to gather and maintain hazard information, encourage research into hazards, and control activities in areas that might be affected by hazards. Haworth’s analysis of Sydney indicates that the Hawkesbury Sandstone capped with Wianamatta Shale has produced poor soils but good building material. Topography, derived from the sub-aerial erosion and extensive dissection of the Permian/Triassic sedimentary strata of the Sydney Basin, has been the strongest constraint on the city’s growth. Steep-sided valleys carved out of sandstone plateaux controlled the direction of settlement. Holocene marine transgression flooded the eastern incisions of the eroded mass, producing some of the few safe anchorages on the southeast Australian coast, as well as bedrock-controlled zeta-curved coastal beaches. Coastal quartz sand deposits produced infertile soils but provided pure sand fill for Sydney’s many attractive beaches, along with industrial uses.
1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 0 2 ) 0 0 1 7 7 - 5
2
Editorial / Quaternary International 103 (2003) 1–2
Willey studied the conurbation of Toowoomba, 125 km west of Brisbane. Toowoomba is mainly floored by basalts and associated rocks of the late Tertiary Main Range Volcanics. Land surfaces including lateritic profiles developed before, during and after eruptions. Subsequent latest Tertiary and Quaternary denudation has resulted in westward migration of the Great Divide with the development of an east-facing escarpment. The topography and soils developed on these rocks provide a range of surficial conditions to be considered in urban planning and development. Nott analysed the urban geology of Cairns, on the northeast tropical coast of Australia. Quaternary sediments provide a record of sea-level change, alluvial and slope response to late Quaternary climatic changes and millennial scale occurrences of various natural hazards. Drying of climate and consequent retraction of rainforest into refugia just prior to and after the Last Glacial Maximum resulted in the construction of extensive high-level alluvial fans and slope deposits which were incised following the amelioration of climate during the early Holocene. Coral micro-atolls suggest that hydro-isostatic rebound following flooding of the continental shelf resulted in a sea-level fall of approximately 1 m since 5.5 ka. Extreme intensity tropical cyclones occur with an order of magnitude more frequently than that suggested by the short (B100 yr) historical record of tropical cyclones from the region. Nott also studied Darwin, which experiences a pronounced wet-dry tropical monsoonal climate. This
latitudinal position has strongly influenced the local geology, and Darwin is dominated by deeply weathered lateritic regolith formed on Cretaceous marine sediments. Models of the landscape evolution of this region, and indeed across much of northern Australia, have been based upon the incorrect interpretation of a type section, displaying weathered Cretaceous strata. A recent reinterpretation of this type section has shown that the landscape here is a function of deep weathering and structural controls within the Cretaceous strata rather than repeated cycles of uplift and pediplanation during the Cainozoic. The six communities discussed in this volume of Quaternary International provide good illustrations of the contributions to be made to urban geology and urban citizens through Quaternary research. Future contributions by Quaternarists to the investigation of Quaternary urban deposits, landforms, and environments throughout the world will continue to provide valuable information and insights.
a
b
Norm Cattoa Department of Geography, Memorial University, St. John’s, NL, Canada A1B 3X9 E-mail address: [email protected]
Peter Bobrowskyb Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada K1A 0E8
Editorial
Urban and Quaternary geology, New Zealand and eastern Australia Urban environments have become home to the majority of people on Earth at the beginning of the 21st century. In nations such as New Zealand and Australia, urban communities contain more than 75% of the population. Resource consumption by urban residents generally exceeds that of rural residents on a per capita basis. Each urban resident of New Zealand and Australia utilizes (at minimum) approximately 100 times the resources used by a rural resident of an underdeveloped nation. Thus, the expenditure of resources by the 1 billion urban dwellers in developed countries is approximately equivalent to that expected from a worldwide rural population of 100 billion. Increasingly, Quaternarists are called upon for investigations in urban environments, lending their expertise and chronological perspective to studies of natural hazards, waste disposal, water supply management, environmental pollution, and town planning. Our perspective, focusing on hominid–environment interactions throughout the Quaternary, provides us with the ability to make valuable contributions to life in urban centres. The multi-disciplinary approach endemic to Quaternary research is particularly suited to study of urban environments in the 21st century. Natural scientists have, as a group, preferred to focus on ‘natural’ environments, both as researchers and educators. Geological field trips may leave town as rapidly as possible; it’s not a ‘real’ field trip until the first gravel road is reached. On some geological maps, the urban areas are left blank, unmapped. Although geologists studying pre-Quaternary materials can discount human influences, this option is not viable for Quaternary geoscientists. Urban Geology has traditionally involved mapping and assessment of the distribution of Quaternary deposits and pre-Quaternary outcrops from the perspective of construction and hazard mitigation. Less concern is given to the linkage between climate (whether ‘natural’, or as it has varied and changed since city foundation) and ongoing geomorphic processes. Although this manifestation of Urban Geology is a valuable asset to Engineering Geology, additional approaches are possible. Relatively few urban geological studies consider the overall influence that Quaternary sediments and landforms have on a particular community, concentrating instead on geotechnical analysis at individual sites.
The papers presented in this volume investigate six communities in New Zealand (Auckland, Dunedin) and eastern Australia (Sydney, Toowoomba, Cairns, and Darwin). Edbrooke et al. investigated Auckland, the largest urban area in New Zealand. Auckland is marked by subdued rolling hills formed on weathered Mesozoic and Early Miocene sedimentary rocks, with many distinctive small volcanic cones. Terrestrial Quaternary sediments crop out in lowland areas and locally interfinger with and are overlain by Quaternary basalts. Geological hazards include slope instability, the threat of renewed eruption within the Auckland Volcanic Field, and the growing recognition of the potential effects of ash deposits from distant volcanic centres. Hazards related to seismic activity are also present. Recent recognition of active faulting close to the urban area has changed the perception of seismic risk. Glassey et al. investigated Dunedin, located on the remains of a Miocene volcanic eruptive centre underlain by Tertiary Late Cretaceous sediments. The geology and topography pose a number of geological hazards, including landslide, mine subsidence, ground-shaking amplification and liquefaction, coastal erosion and tsunami activity. A number of research, policy and planning initiatives have been undertaken to assess and mitigate the effects of these hazards, involving development of a GIS-based Hazard Information System. The Dunedin district plan includes policies to gather and maintain hazard information, encourage research into hazards, and control activities in areas that might be affected by hazards. Haworth’s analysis of Sydney indicates that the Hawkesbury Sandstone capped with Wianamatta Shale has produced poor soils but good building material. Topography, derived from the sub-aerial erosion and extensive dissection of the Permian/Triassic sedimentary strata of the Sydney Basin, has been the strongest constraint on the city’s growth. Steep-sided valleys carved out of sandstone plateaux controlled the direction of settlement. Holocene marine transgression flooded the eastern incisions of the eroded mass, producing some of the few safe anchorages on the southeast Australian coast, as well as bedrock-controlled zeta-curved coastal beaches. Coastal quartz sand deposits produced infertile soils but provided pure sand fill for Sydney’s many attractive beaches, along with industrial uses.
1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 0 2 ) 0 0 1 7 7 - 5
2
Editorial / Quaternary International 103 (2003) 1–2
Willey studied the conurbation of Toowoomba, 125 km west of Brisbane. Toowoomba is mainly floored by basalts and associated rocks of the late Tertiary Main Range Volcanics. Land surfaces including lateritic profiles developed before, during and after eruptions. Subsequent latest Tertiary and Quaternary denudation has resulted in westward migration of the Great Divide with the development of an east-facing escarpment. The topography and soils developed on these rocks provide a range of surficial conditions to be considered in urban planning and development. Nott analysed the urban geology of Cairns, on the northeast tropical coast of Australia. Quaternary sediments provide a record of sea-level change, alluvial and slope response to late Quaternary climatic changes and millennial scale occurrences of various natural hazards. Drying of climate and consequent retraction of rainforest into refugia just prior to and after the Last Glacial Maximum resulted in the construction of extensive high-level alluvial fans and slope deposits which were incised following the amelioration of climate during the early Holocene. Coral micro-atolls suggest that hydro-isostatic rebound following flooding of the continental shelf resulted in a sea-level fall of approximately 1 m since 5.5 ka. Extreme intensity tropical cyclones occur with an order of magnitude more frequently than that suggested by the short (B100 yr) historical record of tropical cyclones from the region. Nott also studied Darwin, which experiences a pronounced wet-dry tropical monsoonal climate. This
latitudinal position has strongly influenced the local geology, and Darwin is dominated by deeply weathered lateritic regolith formed on Cretaceous marine sediments. Models of the landscape evolution of this region, and indeed across much of northern Australia, have been based upon the incorrect interpretation of a type section, displaying weathered Cretaceous strata. A recent reinterpretation of this type section has shown that the landscape here is a function of deep weathering and structural controls within the Cretaceous strata rather than repeated cycles of uplift and pediplanation during the Cainozoic. The six communities discussed in this volume of Quaternary International provide good illustrations of the contributions to be made to urban geology and urban citizens through Quaternary research. Future contributions by Quaternarists to the investigation of Quaternary urban deposits, landforms, and environments throughout the world will continue to provide valuable information and insights.
a
b
Norm Cattoa Department of Geography, Memorial University, St. John’s, NL, Canada A1B 3X9 E-mail address: [email protected]
Peter Bobrowskyb Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada K1A 0E8