Tuesday, 2 July 2013

Planning and initial recce

After a day spent leafing through old books and articles and looking at airborne imagery of the Peak District, we identified a number of interesting sites to go and look for evidence of glaciation.

Meltwater channels?

Brian Whalley and Darrel Swift walking down a possible meltwater channel on the moor above Shatton. In the foreground another channel runs parallel to the one they are walking down. 
On what was a glorious summer's day we met bright and early at the Department of Geography and, after a momentary hiccup getting one of the cars started, made our way up past Shatton to our first field site. Here we had identified a number of parallel channels which, rather than running straight down the hillside, as streams would, cut obliquely across it. This oblique orientation of the channels is common in glaciated regions, where meltwater runs along the sides of the glacier rather than down the slope. As the glacier then retreats, flights of parallel channels can develop down the slope. They are therefore a prime candidate for meltwater channels and would demonstrate the former existence of a glacier in the valley. However, a fierce debate quickly followed, between those claiming that these features were formed by meltwater running along the edge of a glacier, and those convinced that it was humans dragging rocks down to build their farmhouses and drystone walls. Professor Chris Clark explains the problem in this video below.  

To try and resolve this debate we moved further around the hillside to investigate some channel-like features that clearly were formed by farmers carting rocks from pits to build farmhouses and drystone walls. Although the features were similar in dimension to the potential meltwater channels we'd seen earlier, their association with stone pits and their straight nature gave us criteria with which to distinguish them from meltwater channels on future field trips. However, without more detailed field measurements, such as channel width, slope angle and whether they were formed in bedrock or sediment, we were unable to categorically demonstrate that the first channels we visited were formed by meltwater flowing along a glacier margin. 

Glacial sands and gravels on the top of Abney Moor?

After a bumpy ride in the back of one of Chris Clark's Legendary Land Rovers we reached our second site, at the top of Abney Moor, where sands and gravels associated with the last ice age had been previously reported in a geological memoir. We were particularly excited about this as glacial sands and gravels so high up (400 m) would mean a similar ice-surface elevation, and we could also date the sands to get an age on their formation. We spent a good deal of time trying to find these sands and gravels using a hand auger (tool used to bore a hole into the ground and collect a sample of the underlying sediment), but could only find a thick clay/silt unit overlain by peat. The significance of the site is explained by Dr Stephen Livingstone and the augering process demonstrated by Calvin Shackleton (with help from Jeremy Ely) in the video below.

Although we did not find any sands or gravels, despite the memoir, the clay unit does indicate a large lake in the area, which we hypothesised could not have formed without being dammed by ice. We decided that we would return to the area in the near future to take a core through the sediments, and to date the switch from lake to peat formation, by sampling the bottom of the peat unit.

On the walk back to Chris's farm for lunch we stopped to look at a couple of channel-forms identified from the airborne imagery. We were able to rule these out as candidates for meltwater channels, because their dimensions and surroundings were too similar to that produced by human activity (see previous section on meltwater channels).

Moraines at Glossop?

After admiring the animals and eating our sandwiches at Chris Clark's farm we headed off over the Snake Pass to look for evidence of moraines (ridges of sediment deposited by glaciers, often at their snout or along their sides). On the walk out Dr Darrel Swift spotted some erratics in a dry-stone wall (explained in the video below) that were likely to have been brought over by the main British-Ice Sheet, which infringed upon the western side of the Peak district around Glossop.

We were able to discount a number of ridges northeast of Glossop that seemed to be geologically controlled (i.e. due to differences in rock type). This was confirmed by the existence of old pits on the surface of one of the ridges, which would have been used to quarry bedrock (rather than glacial sediments). And similarly, some of the ridges that looked like moraines on the airborne imagery actually turned out to be landslide deposits upon closer inspection. With our spirits dampened somewhat by the lack of glacial features we headed back to the cars. But when we looked back at where we had just been, we identified what looked like a large moraine. We'd been standing on it!
A possible moraine northeast of Glossop. Ice-flow would have come from off the Peak District plateau out of shot to the right of the photo. The steep, arcuate slope on the right hand side of the ridge, its raised profile, and a number of small scars that seem to indicate that it is composed of sediment, together provide the best clues that it is a moraine deposited at the downstream margin of a glacier emanating from the Peak District. 

The day ended with a lengthy discussion in the pub where we evaluated  all the sites again, given the day's discoveries. We decided that there are tantalizing clues which seem to point towards a former glaciation, although the picture is muddied by post-glacial processes, and we still don't know how old the features are. A further recce of other possible sites is required; along with more detailed field measurements and collection of dateable material, to try to constrain the timing of formation of the features we've observed today.

Written by Calvin Shackleton and Stephen Livingstone


  1. The Shatton tracks are documented - they were dug to allow transport from 18th century millstone quarries - although it is conceivable that meltwater features were enlarged and tidied of course.

  2. The Shatton tracks are documented - they were dug to allow transport from 18th century millstone quarries - although it is conceivable that meltwater features were enlarged and tidied of course.