Cymdeithas Daeareg Gogledd Cymru
North Wales Geology Association
Programme :
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Which way to meetings?

Sunday June 12th 2016
Field Meeting: Llanbadrig, Ynys Mon
Leader: Philip Firth

Sunday 3rd July 2016
Cader Idris Volcanism 2
Leader: Graham Hall

Sunday 14th August 2016
Llanberis Slate Formation
Leader: Richard Birch

Thursday 10th November 2016
Assessing the hazard of low frequency, high magnitude landslide events
Speaker: Stephen Parry

Wednesday 23rd November 2016
Gold Rush: Prospecting and Small Scale Mining for gold and diamonds
Speaker: Jim Richards

Wednesday 7th December 2016
Annual Members' Evening - Short Presentations
Speakers: TBA

Saturday January 21st 2017
Annual General Meeting

Wednesday April 26th 2017
A Tale of Two Quakies
Speaker: Mark Easton

June 12th 2016
Field Meeting:
Llanbadrig, Ynys Mon
Leader: Philip Firth
Based on Llanbadrig and adjacent coastal section

The main purpose of this outing will be to investigate the relationship between the Llanbadrig Dyke and the Gwna Melange into which it is intruded. Philip gave a talk at the 2016 AGM on his interpretation of palaeomagnetic fabrics in the dyke exposures here and a number of other localities. There is much else in the vicinity of course. The Gwna Melange is a veritable smorgasbord of geological foods to be savoured.

Gwna Melange
Image ©Jonathan Wilkins. #3468823

The Geologists’ Association Guide (Bates and Davies) records the following:
Gwna Melange, containing sandstone, phyllite, quartzite, limestone, diabase and jasper "producing a many coloured melange that is really indescribeable" (Greenly, 1919). There are also some later igneous dykes (the focus of Philip's thesis), and silicification, pyritization and ferrification. Greenly described this as an autoclastic or tectonic breccia, but a crude stratification can be seen, and it is probably of sedimentary origin.

The terrain is not challenging, comprising a moderate coastal ramble with scrambly bits for the enthusiasts.

LUNCH etc. : The morning session should be complete by 13:00h. There will then be a break of 1 hour for people to go into Cemaes Bay for a comfort station.

Please contact Gary Eisenhauer to register your interest and receive full joining instructions; email address or phone number on the contacts page.

July 3rd 2016
Field Meeting:
Cader Idris Volcanism (2)
Leader: Graham Hall
Based on the Cader Idris and Dolgellau district

Members may remember the excellent field meeting by the Creggennan Lakes which was led for us by Graham Hall, lecturer at Coleg Meirion Dwyfor at Dolgellau. As ever, the subject is too big to aproach in one attempt, so we have organised a second bite at this spectacular geological cherry.

Llyn y gafr
Image ©Hugh Chevallier. #2379482

During the excursion we will investigate a number of interesting issues relating to the Cader Idris volcanic centre. Why are the igneous rocks of extreme basaltic and granitic compositions, with little material of an intemediate silica content present? Why do the mafic intrusions appear as narrow sheets, whilst the granitic intrusions have a huge vertical thickness? Why were the basaltic rocks erupted on the sea bed, whilst rhyolitic rocks appear to be sub-aerial in origin? There are many strands of the geological story for us to unravel.

Starting from the National Park car park at Ty Nant, we will follow footpaths up past the lakes of Llyn y Gafr and Llyn y Gader to the foot of the Cader Idris escarpment. En route, we will examine intrusive and extrusive rocks of the Ordovician volcanic succession, in excellent exposures produced by glacial erosion. Please bring a packed lunch to eat in the spectacular setting of the Llyn y Gader cirque basin. Our return route will take us past slate mines worked in Victorian times.

We will follow the main footpath from the Gwernan Lake hotel up to Llyn y Gafr and Llyn a Gader. This is a steady climb which has no particular difficulties. For the return, we will go across rocky moorland to the old slate quarry, then down the quarry incline. The route is rougher and involves climbing over a couple of walls (about chest height, but quite solid and stable) and crossing one or two shallow rocky streams. Total distance ca 8Km.

Please contact Jonathan Wilkins to register your interest and receive full joining instructions; email address or phone number on the contacts page.

August 14th 2016
Field Meeting:
The Palaeoecology of the Llanberis Slate
Leader: Richard Birch
Based on the Talysarn district, Nr. Penygroes

Culturally, historically and scenically, the Llanberis Slate defines Caernarvonshire, but its palaeoecological significance is little known. The walk will start at Y Fron and look for the (conformable?) boundary with the overlying Bronllwyd Grit in Cilgwyn Quarry, which defines the upper age limit. We will have lunch in Ty Mawr Quarry East, where the scree contains large quantities of green slate suggestive of anaerobic conditions, and in which some bizarre fossils have been found. Afterwards we will return through the quarries to Y Fron, stopping to look at some lichens which colonise slate spoil, and which provide an indication of its chemistry.

Y Fron
Image ©Chris Andrews. #4602584

The walk covers a distance of about 3˝ miles, some of which is up and down a fairly steep incline. For those who wish to avoid this, it is possible to return to the cars after Cilgwyn and drive down to Talysarn. Please note that there are no public toilets or shops in Y Fron or Talysarn.

Please contact Gary Eisenhauer to register your interest and receive full joining instructions; email address or phone number on the contacts page.

November 10th 2016
Assessing the hazard of low frequency,high magnitude landslide events; the role of the engineering geologist.
Speaker: Stephen Parry, Parry Engineering Geology Services
Room CBB115, Best Building, University of Chester.
Location details and map: Find

Tea & Coffee from 18:30h, Lecture commences at 19:00h

During a severe rainstorm on 7 June 2008, over 2,400 landslides were recorded on Lantau Island, the largest island in Hong Kong. Numerous road links were severed and many landslides impinged on existing residential developments. This was one of the most notable storms to have occurred in Hong Kong in several decades, with a 4-hour rolling rainfall equated to a return period of 500-1000 years. A number of the landslides developed into major debris flows, with significant secondary entrainment and long run out distances. Such hazards were underrepresented in the existing data sets at that time.

The presentation will outline the approach to landslide assessments in Hong Kong, discuss the hazard from debris flow with reference to the 2008 storm, illustrate the uncertainty associated with assessing debris flow hazard and examine how this uncertainty can be reduced.

Whilst there are limited historical records of debris flows in the UK, they have been documented in North Wales, the Lake District and Scotland, with the impact on the A83 at Rest and be Thankful being most notable. There is also evidence that the frequency of such events is increasing and the lessons learnt in Hong Kong are useful for the evaluation low frequency, high magnitude debris flows in the UK.

November 23rd 2016
Gold Rush: Prospecting and Small Scale Mining for gold and diamonds.
Speaker: Jim Richards
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Refreshments from 19:00h; Meeting to commence at 19:30h

Gold rushes have had a major impact on world history; from the settlement of California to the development of Australia, and modern rushes continue to shape parts of West Africa, Brazil, Indonesia and elsewhere. This talk follows the journey of British and Australian geologist Jim Richards who has been involved in various modern-day gold and diamond rushes around the world; prospecting, alluvial mining and exploring for minerals.

Y Fron
Image ©Keene Engineering.

This includes time spent in Guyana in South America, mining bonanza grade gold and diamond deposits from the rivers on top of the tepui plateaus of the Pakaraima mountains; hunting for giant gold deposits in the jungles of Laos in South-east Asia; and finding high grade gold mines in the deserts of Western Australia.

Currently, Jim is the Executive Chairman of a publicly listed mineral exploration company based in Perth, Australia. His lead project is an alluvial diamond prospect in the remote Kimberley region of Western Australia which contains some of the world’s finest yellow diamonds, BlinaDiamonds. Jim’s memoir Gold Rush is being published in the UK on 4 November 2016.

December 7th 2016
Annual Members' Evening
Speakers: See below (in no particular order):
Meeting Room, Pensychnant, Conwy.
Meeting to commence at 19:30h
Refreshments and Nibbles from 19:00h
Location details and map: Contact/Find

Gary Eisenhauer:
Fossil lagerstätten of Southern Germany.

A quick tour through three fossil lagerstätten in Southern Germany: Grube Messel, Posidonia Shale and the Plattenkalk. Whilst also taking in some of the museums and other places of geological interest on the way.

Keith Nicholls:
The Ordovician/Silurian Boundary (but in Oslofjord rather than the Welsh Basin).

A brief introduction to the Lower Palaeozoic (specifically - you guessed it - the O/S boundary section) of the Oslofjord Islands and Oslo City hinterland. Illustrated by some of the most joyfully coloured geological maps you will ever hope to see.
I will also have on display two posters I presented at IGCP 591 : Nicholls, Buckley & Wilkins on the Hirnant Limestone, and Nicholls, Appleton and Roberts on the Llyn Geirionydd Graptolites.

Jonathan Wilkins:
Snowdonia Periglacial Geomorphology - off the beaten track.

The upland areas of Snowdonia are rich with the legacy of glacial erosion during the last glacial maximum. Visitor pressure on Cwm Idwal is now so high that parking vehicles can be a limiting factor at popular times. However, there are a number of rewarding and fascinating glacial and post-glacial features close at hand within the rather less visited areas around Llanfairfechan and Abergwyngregyn. This talk will take in some of the gems of the district.

Peter Ellwood:
Kimmeridgian of Portugal

Details on the night.

January 21st 2017
Charting the History of the Yellowstone Super-volcano, USA
Speaker: Dr. Thomas Knott, University of Leicester
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

Super-eruptions are amongst the most catastrophic events at the Earth's surface, with devastating regional environmental consequences and likely effects on global climate.

Yellowstone eruption deposits It is well-known that Yellowstone, USA, has erupted catastrophically in recent times, but possibly less widely appreciated that these were just the latest in a protracted history of numerous catastrophic super-eruptions that left a trail of destruction along the Snake River from Oregon (16 million years ago) to Yellowstone (most recent). New, previously undiscovered, records of super-eruptions are now being revealed in the volcanic record of the central Snake River Plain of Idaho. Characterisation and wide-area correlation of these immense deposits, from one mountain range to another, is hindered by the monotonous nature of the volcanic units, which has limited the use of conventional field-based techniques. Trace-element geochemical analysis has enabled the fingerprinting of individual ash layers. Combined with other techniques (e.g. mineral chemistry and palaeomagnetism) this data can be used to trace individual layers for hundreds of kilometres and to deduce the size of individual eruptions. One such is the newly-defined Castleford Crossing eruption that effectively enamelled an area greater than 14,000 square kilometres with searing-hot volcanic glass around 8 million years ago. The volume of this vast deposit is estimated to have exceeded 1,900 cubic kilometres, with a maximum depth of 1.3 km in the concealed caldera of the super-volcano. The magnitude of this eruption is similar to or greater than better-known eruptions at Yellowstone, and is the first of an emerging record of additional super-eruptions from a period of intense magmatic activity between 12 and 8 million years ago.

Tom will be giving a fine account of this project which was conducted in association with the Universities of California and Idaho, USA, and describing field work in a very challenging and scenically fascinating area

April 26th 2017
A Tale of two Quakies
Speaker: Mark Easton, Opus International Consultants
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

Within the last 7 years, the Canterbury and Marlborough regions of New Zealand' South Island have been significantly impacted by a series of damaging earthquakes. Following a period of relative quiet, the increased rate of seismic activity has created a groundswell in knowledge and corresponding techniques to better understand and mitigate the impacts on civil engineering projects.

This presentation, whilst primarily focused upon geological effects and natural hazards (such as liquefaction and coseismic landsliding), will also cover the wider implications of living and developing in actively seismic countries such as New Zealand, which is currently well deserving of its nickname as 'The Shaky Isles'.

Mark Easton is a Principal Geotechnical Engineer and has worked for Opus International Consultants (Opus) since 2005. Mark has spent the last 11 years with Opus, based in Christchurch, New Zealand and is currently seconded to Opus UK based in the Bristol office.

Mark has spent much of his recent career involved tin the Response and Recovery phases that follow natural hazard events / disasters. Notably, this has included the 2010 Darfield, 2011 Christchurch and most recently the 2016 Kaikoura earthquakes.