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Geophysical applications in geomorphology

Ed.: Lothar Schrott; Andreas Hördt; Richard Dikau

2003. VII, 190 pages, 72 figures, 15 tables, 1 CD, 17x24cm, 520 g
Language: English

(Zeitschrift für Geomorphologie, Supplementbände, Volume 132)

ISBN 978-3-443-21132-5, paperback, price: 89.00 €

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Keywords

Geophysical application Geolmorphologie

Contents

Synopsis top ↑

The use of geophysical techniques has become an important tool in many geomorphological studies. However, the correct handling of geophysical instruments and the subsequent processing of the data they yield, on the one hand, and the description and interpretation of geomorphological settings to which they are applied, on the other hand, are difficult tasks. Without close cooperation of geophysicists and geomorphologists, the accurate and effective use of geophysical techniques and their geophysical and geomorphological interpretation is often limited. There are many text books in both disciplines, but no single book addresses the interdisciplinary aspects of combining geophysics and geomorphology.

This special volume of Zeitschrift für Geomorphologie is intended to bridge the gap between geophysics and geomorphology and to encourage a closer cooperation between researchers in both disciplines. "Geophysical Applications in Geomorphology" is a collection of 10 papers covering a wide range of different geophysical techniques and their integration into geomorphological studies. Most of these papers were originally presented at the International Workshop "Geophysical Techniques in Geomorphology" held in Bonn, Germany in February 2002 with participants (geomorphologists and geophysicists) from Germany, Switzerland, United Kingdom and Norway. The objectives of the workshop were to present geomorphic studies demonstrating the powerful integration of geophysical techniques, to discuss and evaluate the efficiency of different geophysical techniques, give a critical overview of modelling and software tools, to demonstrate the application of different geophysical instruments, and to exchange knowledge and to stimulate research groups with similar interests.

In addition to these papers, we include a CD-ROM by Karl-Josef Sandmeier which contains (i) a test version of the software package REFLEXW (programme for 2D and 3D processing and interpretation of GPR and seismic refraction/reflection data, incl. Demo-data and handbook); (ii) an introduction to the interpretation of seismic refraction data; (iii) an introduction to modelling and tomography tools, and (iv) a technical note on the use of wavefront inversion, forward modelling and tomographic interpretation tools for seismic refraction data

Rev.: THE LEADING EDGE SEPTEMBER 2004, vol. 23 no. 9 top ↑

This English language special issue of Zeitschrift für Geomorphologie (Annals of Geomorphology, special volume 132) contains 10 papers that were originally given at the Inter-national Workshop Geophysical Techniques in Geomorph-ology in February 2002. Periglacial (or paraglacial, the term used in this volume) environment is the geomorphic setting discussed or, more specifically, areas near glaciers with the resulting permafrost and associated sedimentary systems. The purpose of the volume as stated in the preface is to bridge the gap between geophysics and geomorphology and to encourage a closer cooperation between researchers in both disciplines. This special issue has been very suc-cessful in showing how geophysical methods and geomor-phology can be combined to produce meaningful results in understanding the shallow structure, especially the depth and distribution of permafrost. This book s strength lies not in the details of the geophysical theory, but in the discus-sion of how the particular glacial environment affects sur-vey planning, implementation, and interpretation.

I will briefly discuss all chapters, since each contains a great deal of material directly relevant to the field application of the method(s) being discussed, and all deserve attention. The first paper is a theoretical discussion of a glacial sediment system by C.K. Ballantyne; the remaining nine reports are case histories. They are divided by method: three on dc resistivity, two on seismic refraction, one on GPR, and one on RMT (radiomagnetotellurics). The last two chapters discuss an assortment of techniques. The physical property making possible the application of these geophysical meth-ods to permafrost studies is the dramatic change in resis-tivity and seismic velocity that occurs when water and earth materials freeze.

In the second chapter (B. Etzelmüller and others) 10 different geomorphologic sites are examined with the one-dimensional dc-resistivity method. Investigating the application of this method to regions that lack geomorphic permafrost indicators, the authors concluded that the resis-tivity method could not be exclusively used but must be employed with other techniques. C. Kneisel in the follow-ing chapter reaches the same finding and emphasizes the importance of using two-dimensional resistivity surveys, GPR, and seismic refraction in addition to knowledge of the geomorphic and geologic situation. In a digression from these studies in both scale (only a few meters) and application, O. Sass shows how 2D-resistivity methods can be used to determine the wetness of the near surface of out-crop faces. This method could also be applied to archeological studies.

T. Hoffmann and L. Schrott evaluate the intercept-time method and three other schemes used to interpret seismic refraction data and conclude that more than one approach may be required.

S. Hecht, using seismic refraction, describes shallow sub-surface investigations in unconsolidated sediments. He finds that, despite the hidden layer problem, detecting lateral velocity variations are a strong point of this method and par-allel seismic refraction lines were used to illustrate the three-dimensional sediment bedrock interfaces.

Application and limitations of GPR to a region of rock glaciers on Svalbard is discussed by I. Berthling and others. They propose that the 25 or 50 MHz frequencies should be 000 THE LEADING EDGE SEPTEMBER 2004 SEPTEMBER 2004 THE LEADING EDGE 935used, with the former being more difficult to field deploy. Like the other papers in this volume, the authors give detailed advice for the application of the method they are discussing and provide the trade names of the equipment and data interpretation software packages they use. This gives the volume the sense of a field manual.

RMT was used in three investigations by A. Hördt and G. Zacher: the margins of an industrial waste site; aquifer thickness in a groundwater survey (together with seismic refraction); and an agricultural area. The last of these inves-tigations involved searching for shallow cavities. The authors conclude that RMT can be better than dc-resistivity, particularly in rugged terrain where logistics are difficult. They urge the further application of this somewhat neglected approach.

Several methods are discussed in the last two papers. After reviewing dc vertical electrical sounding, resistivity tomography, capacitive coupled resistivity (OhmMapper), electromagnetic coupling (EM-31) and seismic refraction tomography, C. Kneisela and C. Hauck propose that dc resistivity tomography is the preferred single method for alpine permafrost investigations, but recommend that at least one other technique be used to avoid ambiguities.

The longest and concluding chapter (Evaluation of Geophysical Techniques for Application in Mountain Permafrost Studies by Hauck and Mühll) is a comprehen-sive review of nearly all the procedures in the previous chapters, but also includes frequency- and time-domain electromagnetic, and details of bottom temperature studies. All methods are described in tabular form with the first listing applications (with extensive literature referencing), survey personnel requirements, and comments and the second comparing their utility to specific permafrost investigations. These are followed with an explicit discussion of the advan-tages and disadvantages of each with reference to a particular permafrost parameter (e.g., detection, lateral and vertical extent, active layer, and monitoring). Hauck and Mühll rec-ommend the prevailing view of this volume that a combi-nation of dc resistivity and refraction seismic tomography offers the preferred combination of geophysical tools.

While the authors frequently reference SEG publica-tions, most citations are to non-North American journals in the fields of geophysics, geomorphology, and permafrost. This provides the non-European researcher an opportunity to become acquainted with unfamiliar material. A point of interest is the significant differences between the Arctic and mountain permafrost both in respect to geomorphology and apparent resistivities. The book also includes a CD-Rom with a demonstration version of Sandmeier s refraction seismic Demo Reflex W, version 3, together with supporting documents.

I recommend this volume to those working in shallow geophysical studies, but I believe that it is a must for those working in the field of permafrost investigations. Someday astronauts conducting permafrost exploration on the surface of Mars will use these methods.

PATRICK TAYLOR Greenbelt, Maryland, U.S. 936

THE LEADING EDGE SEPTEMBER 2004, vol. 23 no. 9

Bespr.: Zeitschr. f. Geomorphologie Bd. 51, H. 2 (Juni 2007) top ↑

Die Herausgeber Schrott, Hördt und Dikau haben mit 10 interdisziplinären Aufsätzen auf 190 Seiten eine gelungene, englischsprachige Übersicht der verschiedenen geophysikalischen Methoden in der Geomorphologie als Ergebnis eines Workshops im Jahr 2002 in Bonn zusammengetragen. Sie weisen zu Recht auf die komplexen und nicht trivialen Zusammenhänge zwischen technischem Geländeeinsatz, Datenauswertung und sinnvoller Interpretation der Ergebnisse hin und wollen mit diesem Band die zwischen beiden Wissenschaften bestehende Kluft überwinden helfen.

Im ersten Aufsatz stellt der schottische Autor Collin Ballantyne die Rolle geophysikalischer Methoden bei der Parametrisierung eines Modells zur paraglazialen Landformentwicklung vor, das den Sedimenthaushalt in ehemals vergletscherten Gebieten in seiner zeitlichen Abfolge simuliert. Datierungsmethoden und geophysikalische Profile zur Abschätzung des Sedimentvolumens dienen dabei zur Kalibrierung des Modells.

Der zweite Teil des Bandes stellt verschiedene Anwendungsbereiche der ein- bzw. zweidimensionalen Geoelektrischen Tomographie (ERT) in drei Aufsätzen von Etzelmüller et al. (Universität Oslo), Kneisel (Würzburg) und Sass (Augsburg) vor. Sie wird in den ersten beiden Fällen zur Permafrostkartierung (Mächtigkeit, genetische Eistypen) und im dritten Aufsatz zur Ermittlung der Feuchteverteilung in Felswänden mit dem Ziel der Abschätzung der für Verwitterungsprozesse zur Verfügung stehenden Wassermengen eingesetzt. Bei der Kartierung des Permafrostes werden gute Ergebnisse erzielt, Schwierigkeiten treten nur bei homogenen, feinkörnigen Sedimenten auf, wenn die Widerstandsänderungen undeutlich sind (Kneisel). Die Methodik wird allgemein als leistungsfähiges Werkzeug zur Charakterisierung des oberflächennahen Untergrundes angesehen, für eine zuverlässige Interpretation scheint die Kenntnis der geomorphologischen und geologischen Verhältnisse aber unerlässlich. Den dritten Teil des Bandes bilden zwei Artikel zur Refraktionsseismik von Hoffmann & Schrott (Bonn) sowie Hecht (Heidelberg). Hoffmann & Schrott vergleichen vier verschiedene refraktionsseismische Interpretationsmethoden zur Bestimmung der Sedimentmächtigkeit in einer Alluvialebene der nördlichen Kalkalpen. Während die Intercept-Zeit-Methode lediglich bei homogenen und horizontal verlaufenden Schichtverhältnissen eingesetzt werden sollte, kann das Wellenfrontenverfahren zwar höhere Auflösungen bieten, allerdings können durch unterschiedliche Schichten hervorgerufene Geschwindigkeitsunterschiede nicht zugeordnet werden. Komplexere Methoden wie das Network-Raytracing oder die Refraktionstomographie nehmen heterogene bzw. ausstreichende Schichten wesentlich besser auf. Hecht dokumentiert durch die Aneinanderreihung mehrerer zwei-dimensionaler Profile die Möglichkeiten der Abgrenzung pleistozäner Terrassen unter Lockersedimenten.

Im vierten Teil zeigen Berthling et al. die Möglichkeiten des Einsatzes von Ground Penetrating Radar-Systemen zur Aufnahme von Blockgletschern auf Spitzbergen. Reflektionen treten an Materialgrenzen auf, die bei kleinen Blockgletschern den Felsuntergrund, bei großen Gletschern offensichtlich Scherzonen darstellen. Die Autoren empfehlen zur Aufnahme die Verwendung von 50 MHz oder 25 MHz Antennen mit einer Eindringtiefe von 30 m. Bei Winteraufnahmen erwarten sie bessere Ergebnisse (geringerer Energieverlust durch Active Layer). Die Kombination von Längs- und Querprofilen ermöglicht Quasi-3D-Darstellungen des Untergrunds von Blockgletschern. Hördt & Zacher stellen mit der Radiomagnetotellurik (RMT) eine für die Geomorphologie ungewöhnliche geophysikalische Methode vor. Sie verwendet elektromagnetische Felder vorhandener Radiosender, um den spezifischen elektrischen Widerstand des Untergrundes zu bestimmen. Für den routinemäßigen Betrieb scheint das Verfahren aber noch nicht ausgereift zu sein.

Den Abschluß bilden zwei Artikel von Kneisel & Hauck sowie Hauck & Vonder Mühll zum integrativen Einsatz geophysikalischer Methoden bei der Kartierung alpinen Permafrosts. So werden Ein-dimensionale geoelektrische Sondierungen als Vorerkundungen für das Erkennen von Permafrost eingesetzt. Zwei-dimensionale Widerstandstomographie und Refraktionsseismik werden zur kleinräumigen Erfassung sporadischen Permafrosts verwendet. Hauck & Vonder Mühll fassen die Ergebnisse ihrer vergleichenden Untersuchungen verschiedener geophysikalischer Methoden in einer anschaulichen Tabelle zur qualitativen Anwendung in der Permafrostkartierung zusammen.

Darüber hinaus enthält der Band eine CD-ROM mit einer Demo-Version der REFLEXW-Software im Anhang. Damit lassen sich Ground Penetrating Radar, reflexions und refraktionsseismische Daten, Bohrloch- und Ultrasound-Daten verarbeiten und interpretieren.

Insgesamt findet der interessierte Leser hier zwar keine Einführung in die Geophysik, aber dennoch eine gute Übersicht über geophysikalische Methoden und ihre Anwendungsmöglichkeiten in der Geomorphologie. Bei der Suche nach Antworten auf seine geomorphologischen Probleme wird er dadurch angeregt, entweder selbst solche Methoden im Gelände einzusetzen oder sich mit geophysikalisch erfahreneren Fachleuten zusammenzutun.

Volker Hochschild, Tübingen

Zeitschrift für Geomorphologie N.F., Bd. 51, H. 2 (Juni 2007)

Contents top ↑

Schrott, L. & Hördt, A.: Preface: Geophysical Applications in Geomorphology
V-VII
Theoretical issue
Ballantyne, C. K.: Paraglacial landform succession and sediment storage in
deglaciated mountain valleys: theory and approaches to calibration
(with 6 figures) 1- 18
DC-resisiivity
Etzelmüller, B., Berthling, I. & 0degard, R. S.: One-dimensional DC-resistivity
depth soundings as a tool in permafrost investigations in high
mountain areas of Southern Norway (with 8 figures and 1 table)
19- 36

Kneisel, Ch.: Electrical resistivity tomography as a tool for geomorphological
investigations - some case studies (with 7 figures and 1 table)
37- 49
Sass, O.: Moisture distribution in rockwalls derived from 2D-resistivity
measurements (with 11 figures and 3 tables) 51- 69
Seismic refraction
Hoffmann, Th. & Schrott, L.: Determining sediment thickness of talus slopes and
valley fill deposits using seismic refraction - a comparison of 2D
interpretation tools (with 7 figures and 3 tables) 71- 87
Hecht, St.: Differentiation of loose sediments with seismic refraction methods
- potentials and limitations derived from case studies (with 11
figures) 89-102
Other methods
Berthling, I., Etzelmüller, B., Wale, M. & Sollid, J. L.: Use of Ground
Penetration Radar (GPR) soundings for investigating internal
structures in rock glaciers. Examples from Prins Karls Forland,
Svalbard (with 5 figures and 4 tables) 103-121
Hördt, A. & Zacher, G.: The radiomagnetotelluric method and its potential
application in geomorphology (with 10 figures) 123-143
Combined applications
Kneisel, Ch. & Hauck, Ch.: Multi-method geophysical investigation of a
sporadic permafrost occurrence (with 5 figures) 145-159
Hauck, Ch. & Vonder Mühll, D.: Evaluation of geophysical techniques for
application in mountain permafrost studies (with 2 figures and 3
tables) 161-190
Addendum (on enclosed CD)
CD-ROM: Demo-version Reflex version 3.0 (incl. handbook) and introduction to
modelling and interpretation tools by K. J. Sandmeier