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Celebrating an Impact

Celebrating an Impact – Saturday 30th September & Sunday 1st October 2023

The aim of the weekend is to explore the meteorite impact that formed the Stac Fada ejecta 1178 million years ago.  Various speakers will present details of the  processes that take place during such events as well as those specific to the Stac Fada impact.  Topics for future research will be discussed and time will be allocated for a question and answer session.

The symposium is jointly sponsored by the Highland Geological Society and the North West Highlands UNESCO Global Geopark.


Where and When

Saturday 30th Sept will be an indoor session at the Macphail Centre (agenda below) and Sunday 1st Oct will be a field trip to the Stac Fada at Stoer.  For those unable to attend, the Saturday presentation will be streamed online using Zoom.     

Disturbed rock layers and evidence of high pressure gases


Saturday 30th September

The speakers come from a variety of institutions across the UK.

09.30 – 09.45     Registration and coffee

09.45 – 10.00     Welcome and arrangements : Pete Harrison, Geologist, North West Highlands UNESCO Global Geopark 

10.00 – 10.45     Understanding the Process of Impact Cratering – Dr Annemarie Pickersgill, Glasgow University

10.45 – 11.00     Break

11.00 – 12.00     The Stac Fada impact; before, during and after, what we think we know and what we don’t know – Dr Ken Amor, Oxford University

12.00 – 12.15     Break

12.15 – 13.00     Shock Processes learned from Ries Impact Crater applied to Stac Fada – Emeritus Professor Adrian Jones, UCL

13.00 – 13.45     Lunch

13.45 – 14.15     Unravelling the mysteries of the Stoer Group and Stac Fada ‘meteorite impact ejecta layer’ – a mapping  project on Achiltibuie Shore – Dr Patrick Cossey, Stafford University (retired)

14.15 – 14.30      Break

14.30 – 15.30      Lateral variations in the Stac Fada impact ejecta deposit, NW Scotland – Dr Mike Simms, Nat Museum of NI

15.30 – 16.00      Break

16.00 – 17.00      Closing presentation and questions to the panel of  the speakers


The Talks and Speakers

Session 1 : 10.00 – 10.45am

Understanding the process of impact cratering. Dr Annemarie Pickersgill, Glasgow University.

Meteorite impact cratering is the dominant surface process on most terrestrial planetary bodies. While only 200 have been discovered on Earth, understanding impact cratering as a process and understanding the results of impact cratering is key to understanding our planet’s evolution and our Solar System’s, past. I will present an overview of the impact cratering record on Earth, discuss the process of impact cratering and how we can identify impact craters even when they’ve been eroded, buried, or deformed. I will briefly discuss the consequences of impact cratering, both good, and bad, and will end with a brief introduction to ejecta layers, such as the one we have at Stac Fada. 


Dr Annemarie Pickersgill is a planetary scientist and Leverhulme-funded research fellow at the Scottish Universities Environmental Research Centre (SUERC) and the University of Glasgow. Before moving to Glasgow for her PhD she completed a her bachelors and masters degrees at the University of Western Ontario, Canada. Her research has always focussed on impact craters, ranging from Lunar analogue exploration missions in northern Canada to accurately determining when impact craters formed. 

Session 2 : 11.00 – 12.00pm

The Stac Fada Impact; before, during and after, what we think we know and what we don’t know.  Dr Ken Amor, Oxford University

The Stac Fada member of the Stoer Group in NW Scotland has always been considered enigmatic by geologists. It’s re-interpretation as an asteroid impact ejecta blanket in 2008 has only added to the mystery, with alternative interpretations being put forward: eroded and re-deposited ejecta material, post impact melt flow coolant, and glacial deposit (Prof Stuart Robinson pers comm). The occurrence of shocked minerals (quartz and zircon), elevated abundances of platinum group elements and accretionary lapilli, all point to primary material deposited during an asteroid impact and Occam’s razor would suggest that this is the most likely interpretation to account for the observations. Whilst the Stac Fada outcrops show similarities with other terrestrial ejecta deposits, there are some important differences and these require explanation. 

Our current knowledge and understanding of this important rock unit is reviewed in this session. 


Dr Ken Amor is a geologist with a broad interest in the natural world and a focus on geochemistry as a means to understand physical processes that shape our planet. He is a lecturer in Geography at St. Edmund Hall and has been at Oxford University for twenty years. Fieldwork in Scotland lead to the discovery of the large asteroid debris deposit, created during an impact 1.2 billion years ago. He was the first to discover shocked quartz in the deposit. His research interests are varied, spanning the deep time palaeo-environments of the Mesozoic to modern day rivers and traffic pollution.

Session 3 : 12.15 – 1.00pm

Shock Processes learned from Ries Impact Crater applied to Stac Fada.  Adrian Jones, Dept Earth Sciences, University College London WC1E 6BT 

 The surprising physics of shock wave behaviour indicates that hypervelocity impact processes are highly scalable, and that we can calculate and compare the material behaviour of different impact structures using microscopic laboratory experiments to calibrate planetary scale impact processes.  The Ries impact crater is a well-preserved medium-sized (~25 km) terrestrial impact crater,  largely unmodified since its formation nearly 15 Ma ago.  Probably the best-studied impact crater on Earth where drilling has provided rock and mineral specimens of its 3-dimensional deep geological structure, and where Apollo astronauts were trained. Comparisons of the Ries geology and shock metamorphic mineral distribution with the much older Stac Fada impact ejecta could lead to a better understanding of what might be missing and where to look. 


Education mainly at university of Durham (BsC, PhD) then University of Chicago, and Caltech USA, partly in Japan. Classical academic career in UK from Lecturer Polytechnic Kingston Upon Thames 1985-1989 through Reader/Professor of Petrology, University College 1990-2022 where I set up a high-pressure experimental lab (Haskel), taught a large number of igneous, mineralogy, petrology, geohemistry and fieldmapping courses. My research focussed on the petrogenesis of alkaline rocks, rare earth minerals, and carbonatites through experimental petrology, fieldwork and analytical geochemistry (eg ion probe), more recently co-directed European/UK research in sustainable energy funded by three large EU grants (~17M). I was a founder member of the Deep Carbon Observatory (Carnegie Inst. Washington) 2009-2019 covering reservoirs (eg diamond) through to deep life. I have been researching and teaching impact shock metamorphism as a side-line including shocked diamond, since 2000, and have directed around 30 PhD students to success, 5 of whom are now professors. I hold honorary academic positions at the University of Pavia in Italy, and the Natural History Museum London. 

Session 4 : 13.45 – 14.15pm

Unravelling the mysteries of the Stoer Group and Stac Fada ‘meteorite impact ejecta layer’ – a mapping project on Achiltibuie Shore.  Dr Patrick J Cossey: Lecturer in Geology, Staffordshire University (retired)

Recent interpretations of the Stac Fada Member (Stoer Group) as a ‘meteorite impact ejecta layer’ are based on field observations and the analysis of samples collected from coastal sites between Poolewe and Stoer (NW Scotland). While the evidence so far presented supports the notion of a substantial meteorite strike somewhere in the region there remains some uncertainty about the location of the impact crater and much remains to be understood about the deposit itself. Furthermore, literature reviews indicate that, while much is known about many of the larger SFM sites (at Stoer, Enard Bay, Stattic Point and Second Coast for example), little is known about some of the smaller ones, and few of the site descriptions are accompanied by, either large-scale geological maps or detailed sedimentary logs. Inspired by the work of others and a chance meeting with some of the ‘experts’, this presentation reports on an attempt to address some of these deficiencies in the production of a large scale map of one of the smaller SFM sites, on Achiltibuie Shore (locality 30 – Coigach Geotrail) where despite structural complexities, there are features of significant interest!


Patrick is ‘soft rock’ geologist who spent most of his career as a lecturer in Geology at Staffordshire University. He specialised in the development of courses in sedimentology, palaeobiology, petroleum geology, geoconservation and forensic geoscience, and in the delivery of residential field excursions that included regular mapping training courses in the Caledonian Orogenic Belt in Scotland (Southern Uplands, Argyll and Skye). His research interests are broad and lie primarily within the realms of carbonate sedimentology, facies analysis and the evolution of sedimentary basins, and Phanerozoic reef systems. He also maintains a keen interest in geoconservation and the development of geotrails. Indeed, his presence here today stems largely from his recent work on the Coigach Geotrail!

Session 5 : 14.30 – 15.30pm

Lateral variations in the Stac Fada impact ejecta deposit, NW Scotland.  Mike Simms, National Museums Northern Ireland, 

The Stac Fada Member impact ejecta deposit is 4-12 metres thick with an elongate (~50 km), narrow (<200 m), and highly discontinuous outcrop truncated by faulting and/or erosion. Composed largely of devitrified grey or green melt clasts (~20-30% by volume) in a matrix of red muddy sandstone, it appears remarkably uniform, both vertically and laterally. However, this apparent homogeneity masks subtle variations that may provide clues to crater size and location. 

From north to south in general the Stac Fada Member shows: i) a decrease in thickness; ii) a decrease in abundance of steam escape pipes; iii) an increase in abundance of depositional slickensides and shear surfaces; iv) an increased preferential alignment of melt clasts subparallel to bedding and/or shear surfaces; v) an increase in rock fragments from beneath incorporated into the base of the deposit.

Enard Bay, towards the north of the outcrop, is markedly different. Melt clasts, accretionary lapilli and matrix are, in places, profoundly altered compared with other sites, and included rock fragments are surrounded by reaction rims. It suggests that much of the Stac Fada Member here experienced significant metasomatism by high-temperature fluids.

These trends suggest that Enard Bay probably lay closest to the impact crater, with an initially high-temperature (>200oC), highly fluid and non-erosive flow, becoming cooler, more viscous, and increasingly erosive over a distance of ~40 km. This is comparable to observations made at the Ries and Chicxulub impact craters, although Stac Fada differs from them in being a Single Layer Ejecta deposit. Crater diameter is inferred to be of the order of 15-20 km, at the lower end of previous estimates. 


Mike found his first fossils in 1967, at the age of 6. By the age of 9 he had decided to become a geologist and work in a museum and, for the last 27 years, he has worked as a geologist at National Museums Northern Ireland. Mike studied Geology with Zoology at Bristol University, and then a PhD on Jurassic crinoids (a schoolboy interest) at Birmingham University but, since then, his interests have diversified and he has published articles on Jurassic fossils, caves, landscape evolution, meteorites, and much more. In 1987 he discovered the climate and mass extinction event known as the Carnian Pluvial Episode (with his co-author Alastair Ruffell), and has curated several major exhibitions at the Ulster Museum, notably the very popular Elements: From Actinium to Zirconium.

Mike’s involvement in the Stac Fada impact deposit came about purely by chance following a holiday to NW Scotland in 2011. He has published several articles based on his observations and, in 2016, was involved in the Channel 4 documentary Scotland’s Lost Asteroid.


Sunday 1st October

Field Trip to Stac Fada at Stoer.  Minibus transport available from Ullapool to Stoer. 

We will park at the Stoer Cemetery by 10.15am and then walk as a group to the outcrop.  The distance is less than 1 km on a reasonable coastal path.  To see the full extent of the outcrop does required some scrambling over the rock. Minibus places are available from the Macphail Centre in Ullapool, leaving at 9.00am at a cost of £9 per person. Car sharing is encouraged by those not travelling by minibus. An additional emergency contact form will need to be completed if attending this day.



Bring your own lunch on both days. Tea and coffee making facilities will be available at lunchtime on the Saturday.

Tea and coffee will also be available during the morning and afternoon breaks at the Macphail Centre on the Saturday.



There is ample parking at the Macphail Centre in Ullapool for the Saturday and limited parking at the cemetery at Stoer for the Sunday. Car sharing and use of the minibus for the Sunday is encouraged.

Evidence of impact ejecta with accretionary lapilli and the remains of vitrified materials


Booking and Prices

The cost to attend each day in person or online is £9 or £5 for Geopark Ambassadors, Friends of the Geopark and members of the Highland Geological Society.

Minibus places for the Sunday field trip can be booked at a cost of £9  (numbers will be limited and are available on first come first served basis).

To reserve your place please complete the booking form below and make your payment. Payment can be made using BACS with the bank details below.  Please tag the payment with your name.  Once payment has been received your place will be confirmed. 

Account Name : Northwest Highlands Geopark

Sort Code : 83-28-01

Account No : 00107691