Geomorphologic Mapping

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Self-isolation has benefits; time is available to look at collected materials stretching back many years. In the words of the late lamented John Chappell, “I went digging deep into one’s stratigraphy”. It is a time of re-discovery, finding materials long stored in boxes, cupboards, and map rolls. What a delight to find the products of old mapping and then chase up the labours of others who have been involved in landform mapping.

In first year Geography at Sydney University, Trevor Langford-Smith had us pouring over topographic maps, mostly from the USA, to identify landform types. This was as close to heaven I could reach at the time! It stimulated an interest in geomorphology reaching into the literature of Andrews, Taylor, Craft, and others. They formulated the landform history of eastern Australia without the aid of air photos but used an emerging understanding of bedrock geology and lots of field work.

My own adventures in mapping commenced in 1960 when I was turned loose in the Port Stephens-Myall Lakes area as an honours student. This was “exploration” mapping. No previous attempt had been made to depict the types and distribution of coastal landforms in an area rich in various depositional features. Last week I found my old base map annotated with observations which I had cross-checked from air photos. I adopted a simple but laborious method: study stereographic air photo images, then make transects across the land in as many places as possible to be confident in what the photos show makes sense. As strange as it now seems this gave me a perspective that locals did not have and led me to give a talk to local Rotary before I submitted my thesis.  It also enabled me to contribute to the Newcastle 1: 250,000 geological series being prepared at that time by Brian Engel of Newcastle University (Geol. Survey NSW, 1966). This was a real thrill as Brian made me feel my work as a geography student was useful by adding Quaternary information to a geologic map and its explanatory notes. While doing my PhD work at LSU I was again able to contribute to geologic mapping while assisting the South Carolina Geological Survey, and also to discussions with USGS personnel, such as Bob Mixon, undertaking Quaternary mapping in North Carolina.

Geomorphologists approach the business of map making from different points of view. Like my first attempt it can be exploratory trying to work out where features occur and are there any patterns that make sense in relation to known events that may have produced these different landform types. In some places the bedrock geology forms a framework from which the process of mapping can commence. With experience the mapping forms the basis of conceptual models that can be tested in different locations. Peter Roy was a master of this process as seen in his many publications on the Quaternary geology of the NSW coast.

Tools available for mapping have changed over time. From horse back field surveys, to use of topographic and other base maps, to analysis of air photos and later satellite images, and more recently LiDAR, geomorphologists have been able to develop ways to unravel the evolution of landforms. As Douglas Johnson so eloquently explained in his essays on method many decades ago, these maps provide a basis for inference on processes that have operated in the past. But new technologies open eyes to new patterns and create opportunities for reinterpretation of landform history on land and beneath the sea. I will never forget the time several years ago in Perth with Ian Eliot studying marine LiDAR images off the SW coast of WA where preserved calcarenite features on the inner shelf revealed topographies long since drowned by rising sea levels. We are now benefitting from similar images on the east coast building on previous marine surveys by Gordon, Roy, Lean, Phipps, Albani and others (see Linklater et al., 2019, Geosciences, 9 (1)).

It would be remiss of me not to mention a few examples of geomorphic mapping that not only was invaluable for helping know more about landform evolution but also contributed to broader understanding of landscape history and dynamics.

At one scale is what could be termed micro-scale mapping based on a combination of air photo interpretation and field survey. David Stoddart’s 1962 study of three Caribbean atolls in British Honduras is a classic of this type. It was published as a report from the Coastal Studies Institute, LSU, sponsored by the Geography Branch, US Office of Naval Research. This study captures in detail the method used many times in David’s career of traversing atoll with compass, level and at times plane table in a very traditional survey procedure adopted by many Cambridge University geomorphologists.

At a very different scale is the work of geomorphologists who formed the survey teams in the CSIRO Division of Land Use Research at CSIRO. Initiated by their Chief, Chris Christian, on the early 1950s, these teams mapped and described vast tracts of Australia and PNG. Each team had a geomorphologist helping to assist ecologists and soil scientists interpret “land systems”. Galloway, Mabbutt, Twidale, Williams and others built their careers around this work. A visit to the CSIRO Black Mountain Lab in 1958 and discussing this work with Jack Mabbutt was a source of personal inspiration. Digging out a Land Research Series report today continues to thrill me.

While in the USA I became familiar with another lab. This was the huge US Army Corps of Engineers Waterways Experiment Station at Vicksburg, Mississippi. In the 1940s the War Department commissioned Harold Fisk of Geology at LSU to study alluvial deposits and their effects on Mississippi River activity. In 1947 he produced a two-volume report of which I am very lucky to own a copy. This work involved detailed mapping of alluvial landforms and provides a model of changes in river behaviour in the Holocene. Of course more work has been undertaken since then. In 1994, Roger Saucier who obtained his PhD at LSU, completed a revision of the Fisk study. His work, also a two-volume set, was published by the Mississippi River Commission. My copy of this set reveals a magnificent colour set of maps at a large scale with a further revision of depositional history initiated by Fisk and others. To me this is one of the gems of landform mapping.

Finally I must comment on the work of John Hack, one of my heroes of the discipline. Anyone familiar with geomorphic theory will have read Hack’s 1960 paper in the American Journal of Science. I had the privilege of spending time with him in the Carolinas and Delaware. He was a great field man following the tradition of his 19th century hero in the USGS, G.K. Gilbert. He wrote a number of USGS Professional Papers based on a thorough understanding of bedrock geology, for example USGS Prof. Paper 484 and 504-B). In these studies he mapped landforms to help test his model of landform evolution. One co-authored paper (Prof. Paper 347) really resonated with my eco-geomorphology studies of mangrove ecosystems; this was his study with John Goodlett, a forest ecologist from Harvard. Their work in the central Appalachians involved detailed mapping of forest types and linked their distribution to landform and soil conditions and impact of 1949 floods on vegetation. I saw elements of the CSIRO multi-discipline thinking, the need to know the geologic history and the ability to map landforms at a more micro level all wrapped together in this must-read paper.

 Bruce Thom

Words by Prof Bruce Thom. Please respect the author's thoughts and reference appropriately: (c) ACS, 2020, for correspondence about this blog post please email austcoastsoc@gmail.com

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