Landscape evolution in the lab – the early experiments by Adolf Wurm

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Together with empirical work in the field and numerical modelling, laboratory experiments are an integral part of geomorphological research. The importance of these experiments derives from the controlled setting that we rarely (or actually never) have in nature and which allows us to investigate specific processes in isolation. Moreover, most processes and their evolving interactions in real landscapes take too long to be directly observed by humans. Experiments allow us to accelerate the pace of landscape evolution and to study these processes in hours or days while they may take thousands to millions of years in reality.

Video still of one of Wurm’s movies.

One of the major difficulties in the design of experiments is to get the scaling right. Do the experiments correctly represent the relative roles of e.g. hydraulic stresses, grain sizes, coherent forces between grains, etc. at the small spatial scales to be relevant for the understanding of landscape evolution? It may be these questions and doubts that caused that experimentalists had a hard time in scientific communities that largely relied on field observations and conceptual models of landscape evolution and often perceived experiments as “too simple to conform with reality” (Bremer 1989 in Skowrownek 2021)

A researcher, whose experimental work remained largely unseen until today, is Adolf Wurm. The German geologist performed numerous experiments at the University of Würzburg as early as in the 1930s. His experiments involved setups to study forms such as cuesta landscapes, slope profiles, peneplains and piedmont benchlands. Recently, Armin Skowronek, professor for regional soil science at the University of Bonn, rediscovered Wurm’s experimental works and summarized them in a paper which I like to highlight here. Moreover, Armin Skowrononek and Jens Turowski were able to track the films made by Wurm, digitized them and made them available online.

Here is the list of movies available:

C 121   Headward erosion https://doi.org/10.3203/IWF/C-121
C 123   Earth pyramids https://doi.org/10.3203/IWF/C-123
C 136   Fluvial terraces https://doi.org/10.3203/IWF/C-136
C 157   River capture https://doi.org/10.3203/IWF/C-157

I think that the videos of these very early experimental works in geomorphology constitute a real treasure. They depict the processes and their pure physical action in the absence of other processes such as weathering or the influence of vegetation, and thereby provide often simple explanations for landforms whose occurrence has been ascribed to complex weathering-denducation feedbacks during certain climatic conditions (morphoclimates in the sense of representatives of climatic geomorphology).

Nowadays, experimental geomorphology has long left a niche existence (for an example with TopoToolbox see here). In part, this may be also due to better topographic surveys of these experiments which enable researchers to track surface changes using repeat high-resolution DEMs, and to precisely measure runoff and sediment discharge. These developments in quantitative geomorphology go hand-in-hand with developments in numerical landscape evolution models. Still, Armin Skowronek notes that experiments in geomorphology are still missing out in text books on earth surface processes. Future text book-authors may wish to fill this gap.

References

Skowronek A. 2021. Morphological analysis and experiment – The fascinating results of the Wuerzburg geologist Adolf Wurm (1886–1968). Zeitschrift für Geomorphologie : 291–312. DOI: 10.1127/zfg/2021/0686

Open PhD position in the project SEDITION

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Here is a recent vacancy at the Freie Universität Berlin. Deadline is the 6 September 2021. Go for it! The full text with all information is found here.

The research groups “Sedimentary Systems”, “Cosmogenic Nuclides” and “Physical Geography” at the Department of Geosciences of the Freie Universität Berlin are jointly seeking a candidate for interdisciplinary research on the dynamics of erosion and vegetation in the western Mediterranean. The position is to be filled for 4 years starting from October 1st, 2021.

In the inter-institutional project SEDITION (Dynamics of EroSion and VEgetation in the Western MeDITerranean Region reconstructed by couplIng proxy data (cOsmogenic Nuclides, biomarker) with geomorphological evidence and modeling approaches), we will investigate the influence of human settlement history on vegetation and erosion in the immediate hinterland of three selected sites in the Western Mediterranean. Innovative methods (two cosmogenic nuclide systems, biomarkers, modeling approaches) will be used to characterize erosion rates and vegetation changes.

Job description:
• Geomorphological/sedimentological field work in Italy, Spain and Tunisia.

• Quantification of paleovegetation and hydrology using terrestrial biomarkers.

• 2 semester hours per week (SWS) teaching at the Institute of Geological Sciences

• Presentation of results at international conferences and in scientific publications

• Working in a team with other PhD students, postdocs and staff members

  • · Preparation of a doctoral thesis
  • · The activity serves the scientific qualification

Requirements:
• Completed university degree (MSc.) in geosciences

Desirable:
• Sound knowledge of basic chemistry

• Experience with chemical laboratory work

• Excellent organizational and problem-solving skills and the ability to work both independently and as part of a multidisciplinary team

• Proficiency in written and spoken English, and (if not already present) a willingness to learn German

• Experience with cosmogenic nuclides

• Experience with terrestrial biomarkers

• Knowledge of statistics and geographic information systems

• Interest in research on human-environment interactions

• Modeling skills

• Class B driver’s license

For more information (where to apply, reference code, …) go here.

Mean basin ksn and smoothing madness

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This post is written by Richard Ott, PostDoc at the GFZ Potsdam. Richard’s research focuses on tectonic geomorphology, but he has also been working on diverse topics bringing in his expertise in geomorphometry, cosmogenic nucleides and other analytical and numerical techniques. Also see Richard’s website: https://richardott.weebly.com/

Ksn is one of the standard topographic metrics used in tectonic geomorphology. Based on the stream-power model it is typically interpreted as a proxy for rock uplift, provided steady state topography. Often, we are interested in the mean ksn of a drainage basin. Especially, when we measured catchment erosion rates (e.g. from 10Be), ksn is a predictor candidate that potentially explains much of the variability in between different catchments. This sounds like a very simple and straightforward task. In this blog post I’ll try to convince you that – as with most things in life – the devil is in the detail…

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Export a PPS instance as shapefile

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A TopoToolbox user recently commented on this blog and asked how to export a set of knickpoints stored in an instance of a PPS object to a shapefile. As this is likely a question that many would like to see answered, I thought I devote a short blog post to it.

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Calculating mountain prominence

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If you like hiking and climbing, you may know the term peak prominence. According to wikipedia, topographic prominence is “is the minimum height of climb to the summit on any route from a higher peak, or from sea level if there is no higher peak.” (Wiki).

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Mid-European Geomorphology Meeting 2021

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We will have a Mid-European Geomorphology Meeting on Nov. 6-9 in Munich this year. The conference will be hybrid with people attending in person but also virtually. Hence, you may participate if you are fed up with online conferences, but also if you do not have the time or money for travelling to Munich. The organising and scientific committee has elaborated an exciting programme with diverse sessions.

Please read more about here. Hope to see you there!

Hindcasting and nowcasting rainfall-induced landslides – do global precipitation estimates help?

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In July 2017, an unusual torrential storm hit southwestern Japan in Fukuoka Prefecture triggering more than 2000 landslides within 12 hours. Unlike the seemingly large extent of the overall rainfall activity, landslides were concentrated in a small area of about 200 km2, where total rainfall accumulation exceeded 500mm. A year later, trenching rains during a larger weather system for about 5 days affected the entire southwestern Japan. This time, the week-long rainfalls triggered about 8500 landslides in an area of 3000 km2 with spatially highly variable rainfall accumulations. The contrast between these distinct events motivated us to explore the usefulness of global grid rainfall data, such as GPM IMERG (Integrated Multi-satellitE Retrievals for Global Precipitation Measurement) and ERA5 climate reanalysis data, for landslide hindcasting or nowcasting.

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Anatomy of a Himalayan cascading disaster

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It was on the morning of Sunday, the 7th of February 2021, when I checked my Twitter account, and my friend and colleague Basanta Raj Adhikari had noticed me about a massive flash flood in Uttarakhand. With the first images and videos appearing on social media, the scale of the disaster became quickly apparent. As numbers of known fatalaties rose, media outlets started reporting about the event, iterating speculations about a glacial detachment that had caused the flood.

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Where and why do submarine canyons remain connected to the shore during sea-level rise?

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Bathymetric and topographic model of the northern Mediterranean Sea. Data from opentopography.org.

The world’s shelfs are dissected by steep canyons which act as conduits of terrestrial sediments to marine-depocenters. The spatial distribution of these canyons, however, is neither uniform nor completely spatial random along the continental margins. In particular, there are profound spatial differences in the occurrence of canyons that extend back to the shore line and those that have their heads close to the continental slope.

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Ksn anomaly plot with confidence bounds (or how to distinguish knickzones from knicknoise)

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In response to my previous post, Philippe Steer from the University of Rennes came up with an idea that I’d like to explore a bit more here. In brief, I posted a code and figure that showed an anomaly plot of Ksn and Philippe suggested to have confidence bounds around the mean so that one could identify Ksn values that go beyond the noise inherent in data of longitudinal river profiles. To this end, such analysis would be needed if you want to objectively distinguish knickzones from the noise.

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