Cymdeithas Daeareg Gogledd Cymru
North Wales Geology Association
Programme :
2017-18
at a
Glance
Which way to meetings?

Saturday January 27th 2018
Annual General Meeting

Wednesday February 21st 2018
Monitoring subsidence related to relict salt mine, Marston, Cheshire.
Speaker: Cathrene Rowell, Keele University

Wednesday March 28th 2018
Epic seafloor off North Wales.
Speaker: Katrien Van Landeghem, Bangor University

Sunday July 29th 2018
Field Meeting: Pen yr Henblas Quarry, Halkyn
Leader: Chris Twigg

Sunday August 19th 2018
Field Meeting: Benllech, Red Wharf Bay
Leader: Jonathan Wilkins


Saturday
January 27th 2018
ANNUAL GENERAL MEETING and
Speaker: Dr Servel Miller, University of Chester
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Annual General Meeting commences 10:00h
Refreshments at 11:00h
Lecture to commence at 11:30h
From Diatoms to Drones: A Journey from Mapping Tsunami on the shores of Jamaica to Slope Instability along UK Coastlines.

Recent events such as the January 2018 mudslide event in Montecito, California are stark reminders of the disproportionate impact that such natural phenomena can have on society. In areas that have not experienced the effects of an adverse natural hazard in living memory, raising awareness can be challenging, particularly if there is limited knowledge and understanding of the risk posed to society. Identifying, mapping and quantifying these hazards is thus one of the most important steps in their management.

Within areas affected by natural hazards such as tsunami and slope instability, deposits and/or geomorphological features left in the landscape can provide vital evidence of hazard existence, extent and magnitude. In Jamaica for instance, the last tsunami was in 1906. The island as such has very limited plans to mitigate the potential impact of a tsunami, mostly due to the lack of evidence for their existence. In the UK landslides, unlike flooding, are rarely considered during the planning processes but there has been a three-fold increase in landslide incidents in the last decade, costing millions of pounds each year. One problem that geologists face is the difficulty in obtaining accurate records of landslide events, especially in more remote areas. This talk will explore the use of novel techniques such diatom analysis to determine the extent of tsunami deposits in Jamaica and the use of drone mapping techniques to map landslides in inaccessible valleys and unstable cliffs around the UK. However, these tools/techniques are not without their challenges and limitations, which will be explored as part of the talk.

Dr Miller is senior lecturer and programme leader for the BSc. Natural Hazard Management course in the Department of Geography and International Development at the University of Chester.
Wednesday
February 21st 2018
Monitoring subsidence related to relict salt mine, Marston, Cheshire.
Speaker: Cathrene Rowell, School of Geology, Geography and the Environment, Keele University
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

The Cheshire Basin contains >4.5km of Permo-Triassic red beds, including the Mercia Mudstone Group (MMG) which accumulated in playa and tidal-flat environments. The MMG is the host to two major halite formations: The Northwich and Wilkesley Halite formations, which have been commercially exploited. Both rock salt and brine has been extracted from mainly two horizons of the Northwich Halite Formation in the Cheshire Basin in various locations, and rock salt is still mined in nearby Winsford, Cheshire.

canal subsidence Surface subsidence resulting from salt mining and brine pumping in Northwich, and the surrounding areas in Cheshire, has occurred since Medieval times. This has varied in severity, with evidence of subsidence ranging from topographic depressions to catastrophic surface collapse from the mid-18th Century onwards.

To detect, characterise and monitor areas susceptible of subsidence, near-surface geophysics has been applied. A section of the Trent and Mersey Canal, in Marston (Northwich), crossing 3 abandoned salt mines has been the focus of long-term microgravity surveys for >10 years. The data collected over this period shows consistent, deepening negative anomalies at the margin between the Adelaide and Old Marston relict mine workings, as opposed to over the mines themselves. By correlating microgravity data with mine plans, boreholes and sedimentary logs, 2D gravity models have been produced: the anomalies are interpreted as upwardly propagating voids, and associated collapse material. A void feature at the point of the microgravity excursion has been confirmed by intrusive investigations. Further investigation of the canal water depths and the underlying silt accumulation on the canal floor has been undertaken, in addition to water / sampling and analysis, to ascertain any connection to underlying mines and potential canal collapse. This study further demonstrates the importance of time-lapse microgravity surveys to facilitate the identification and monitoring of at-risk areas, with a view to mitigating the risk of catastrophic surface subsidence.

Cathrene Rowell is studying for her PhD at Keele.

Wednesday
March 28th 2018
Epic seafloor off North Wales shows rapid ice retreat during the last ice age. The fate of West-Antarctic ice?
Speaker: Dr. Katrien Van Landeghem, School of Ocean Sciences, Bangor University
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

antarctic science cruise A spectacular 2100 km2 seafloor image dataset collected on behalf of Celtic Array Ltd between Anglesey and the Isle of Man reveals the geomorphology and subsurface geology of a wide, submerged glacial landscape. With this data, we investigated how the Irish Sea Ice Stream advanced and retreated about 20,000 years ago (during the last ice age). This ice stream was the largest of its type to drain the interior of the former British-Irish Ice Sheet, and this study thus provides a conceptual model of how large ice streams retreat and cause the instability (even collapse) of large ice sheets. Why is that so interesting or important? Some ice streams in West Antarctic Ice Sheet are currently also unstable and there are concerns that their retreat can cause an onset of rapid collapse of parts of this massive ice sheet. That in turn would cause a huge global sea level rise (in the order of metres), and warrants our greatest attention.

Katrien is a lecturer and researcher in the School of Ocean Sciences at Bangor. Her current research includes sand dredging, sediment transport, shipwreck sites and the future of the Antarctic Ice Sheet. She is an engaging speaker and this talk will appeal to anybody with an interest in the special area we call the Irish Sea. N.B. This sea has equal claim to be Scottish, English and Welsh, and it matters to all of us! Her image (left) bears an uncanny resemblance to the view of the Carneddau from the Menai Strait during chilly times, don't you think?

Sunday
July 29th 2018
Field Meeting:
Pen yr Henblas Quarry
Leader: Chris Twigg and Tom Hughes, NEWRIGS
Based on the Pen yr Henblas Quarry, Pentre Halkyn

This field trip is a follow up to Tom Hughes short article in Newsletter 97, and to the brief "taster" visit a number of us made to the western quarry high wall last summer.

Pen yr Henblas Quarry"Pen yr Henblas quarry is of regional geological importance because it has excellent exposures of the Lower Carboniferous Pentre Chert and Cefn Mawr Formations. There is also exposure of the regional unconformity between the Pentre Chert and the underlying Cefn Mawr Formation".

There is a lot to see here, in spectacular exposure. The site is an abandoned quarry, with open public access, and opportunity to park nearby. In the quarry itself, there are the usual precipitous walls, spoil heaps etc, but it is only a short walk from the car park area, into the quarry, and this should not be considered an arduous trekking visit.

Please note hammering should only limited to breaking up existing fallen debris (there is plenty of it). As well as the usual brachiopods and corals there have been a number of sharks' teeth, and a coelacanth jaw recovered from this quarry.
News hot off the press: Chris Twigg has promised to bring along the coelacanth jaw!

Once we have finished fossicking in the quarry, there are plenty of interesting outcrops of Carboniferous Limestone, and old mining archaeology in the surrounding landscape to walk about in.

Please contact Keith Nicholls to register your interest.

Image ©Dave Dunford. Geograph.org.uk #4418887

Sunday
August 19th 2018
Field Meeting:
Benllech, Red Wharf Bay/Traeth Coch
Leader: Jonathan Wilkins
Based on the upper shore of Red Wharf Bay, nr Benllech, Anglesey

Carboniferous Karstification

Trwyn Dwlban

This meeting is designed to appeal to members who do not relish arduous upland or subterranean rock exposures; instead we take to the traditional Welsh seaside for a look at the Carboniferous Limestone of south-eastern Anglesey.

Cyclic sedimentation is well-known in this formation, where thick beds of limestone are interrupted periodically by mudstone beds representing deeper water. However, emergence of the limestone surface due to lowered sea level allowed the development of a Carboniferous karst surface which has been exposed to modern view as a result of erosion. Subsequent to the development of the karst surface, renewed sedimentation as the relative sea-level rose once more resulted in sandstones being deposited into the features of the karst surface. The modern exposure of these features include in-filled pipes and isolated sandstone columns where limestone has eroded from around them. It is claimed that these exposures are unique in the British Carboniferous!

Join us for a very gentle rocky-ramble, whose maximum elevation is around 5 metres and whose maximum length is around 1000 metres, depending upon where you park your vehicle. Full facilities are available in nearby Benllech, and we have checked that low tide is at mid-day.

Please contact Jonathan Wilkins by email or telephone to register your interest.

Image ©Jonathan Wilkins (not Geograph this time).