Estimating Sandur Volume

Michael Singer
University of St Andrews
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This 6 hour exercise is designed to teach students how to make 'quick and dirty' estimates of sediment storage in the field. It leans on surveying skills and basic mathematics.

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This exercise was employed in an upper division, undergraduate field course in physical geography for majors.

Skills and concepts that students must have mastered

Basic survey skills. Basic math.

How the activity is situated in the course

stand-alone exercise


Content/concepts goals for this activity

To make a rapid estimate of sediment stored in a landform that will raise further questions about the sources and timing of its delivery.

Higher order thinking skills goals for this activity

One of the challenges of observing landforms is understanding the processes by which they are created. This simple exercise attempts to partially address this by quantifying a stored volume of sediment where there exist suitable temporal and spatial constraints. In this vein, a rudimentary estimate of sedimentation rate may be inferred and hypotheses may be generated.

Other skills goals for this activity

operation of relevant survey equipment (e.g. total station, autolevel, rangefinder)

Description of the activity/assignment

Sandurs tend to develop downstream of glaciers, especially as they recede, but the rate of accumulation is poorly defined. This activity was conducted on the Nigardsbreen sandur in the Jostedalen Valley of Norway, where the glacier retreats are well known. Spatially, the lake in which the sandur has formed is bounded by bedrock on the upstream side and the depth to bedrock in lake's midsection is also known. The task then is to survey the surface of the sandur along several transects (each group surveys one transect of their collective choosing) and use these surveys with the bedrock assumptions to estimate the volume stored in the sandur. Since the glacial retreat rate is also known, an average rate of infilling may also be calculated. I instructed the students to make both estimates in the field via simple calculations (e.g. assuming the deposit is triangular). Then I sent them searching for likely sediment sources (dirty glacier, paraglacial landsliding, etc) that may have built the sandur. They use this field assay to generate hypotheses about how and on what time scale (e.g. episodically v. gradually) the sandur formed. In essence, they learn to think like geomorphologists.
Designed for a geomorphology course
Integrates geomorphology into a core course in geology
Addresses student fear of quantitative aspect and/or inadequate quantitative skills

Determining whether students have met the goals

The beauty of the activity is that the long profiles surveyed by each group were very similar compared with the scale of the boundary conditions, so the results of their calculations are precise within ~10%.

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