Nice to see both ‘teacher’ and ‘student’ aspects of positive teaching. There’s a challenging balance for the university lecturer – how to be ‘open/available/leading by service’ while not spoonfeeding.
I had the opportunity to visit Carskiey Beach this summer while on
a field trip holiday. It’s a beautiful beach, located at the southern tip of the Kintyre Peninsula, Argyll, Scotland. It’s well worth a visit. When we were there, there were up to four other people on the beach.
The modern beach is quite interesting as it acts as a barrier to a small river. It would be fascinating to see borehole logs from behind the beach. At the east end of the beach is an outcrop of the Glenramskill Formation, which is part of the Dalradian Supergroup (http://data.bgs.ac.uk/doc/Lexicon/NamedRockUnit/GRK.html; Browne e al 2002, http://nora.nerc.ac.uk/3231/1/Devonian%5B1%5D.pdf). In the old terminology, it was known as part of the Old Red Sandstone, which I find a more user friendly, albeit less scientifically-precise, name. The rocks date to the Devonian Period, and specifically the Lochkovian Stage (419.2 to 410.8 million years ago) when this part of the world formed part of the Laurasian landmass (see the palaeogeographic map at http://bit.ly/1vE4ajq).
Recent storms have cleaned off much of the outcrop so the bedding can be clearly seen. The lithologies range from coarse breccias and sandstone, to fine sand/siltstone. The finer beds are typically red-brown. There is evidence of reworking in the form of rip-up clasts, and of post-depositional/pre-lithification deformation which may reflect rapid burial of wet sediments, or some sort of vibration.
Although I normally focus on Quaternary-age things, I find these old rocks fascinating. Despite their great age, the individual beds actually represent events over seconds or minutes. This would have been a wide river plain with channels and pools, the water bringing rock detritus from mountains made of even older rock. Similar processes are depositing and reworking are taking place in the river where it cuts through the beach nearby.
This link between the ancient and the modern is one of the things that makes geology such an exciting subject.
Fantastic photos with great detail. Thanks for posting!
Really interesting article on Mary Bourke’s Planetary Geomorphology image of the month blogsite by Bourgeoi et al. on possible ancient (3.5 Gy) glacial features in the Valles Marineris, Mars, including an image of a stunning landslide where runout length may reflect basal ice.
Post by O. Bourgeois, M. Gourronc, D. Mège and S. Pochat – Laboratoire de Planétologie et Géodynamique, Université de Nantes, France
The current climate on Mars does not allow for significant accumulations of surface ice at low latitudes. Therefore ice is only found at the two polar ice caps and in a number of ice-filled craters scattered at northern and southern latitudes (> 70°).
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Nice blog on a great geo-site. Cwm Idwal also has a large rock fall on the backwall slope – possibly a deglaciation unloading feature?
Every year I bring students from Bangor University on a fieldtrip to Cwm Idwal in Snowdonia.
It is always a thrill to tell them they are walking in the footsteps of Charles Darwin who came here to learn geology before he embarked on The Beagle.
Cwm Idwal was Wales’ first National Nature Reserve designated in 1954. It is one of the best places in the country to see the effects of glaciation and to learn to recognise the features of this dramatic ice scoured landscape. A glacial ridge holds the lake, Llyn Idwal, against the base of the cliffs which define the natural amphitheatre.
In Cwm Idwal the geology also acts as a stage for spectacular ecology. The cliff faces serve as hanging gardens for several species of Arctic-alpine plants, including The Snowdon Lily (Lloydia serotina). My students come to see…
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There’s been increasing promotion of the term “Anthropocene” in the last few years. There are some very active proponents and, as with many things where it seems like someone else’s business, a possibly larger group of people who haven’t engaged with it to date. That may change if it gains favour and starts to impact on this latter group in, for example, the likelihood of getting research grants and papers published.
A recent article in The Independent newspaper reports on the idea of the Anthropocene, particularly highlighting the proposal that a new formal geological period should be defined, covering the period during which there has been a clear signal of human activity preserved in the geological record. This article followed a focus on the Anthropocene during the recent EGU conference. An excellent blog by Daniel Schillereff reports on the associated press conference. Unfortunately, I wasn’t at this year’s EGU due to work pressures but the idea has been bouncing around for a few years now, so it’s not all new.
As you can imagine, there has been a certain amount of debate around this proposal – rightly so as the formal stratigraphic system, as defined by the International Commission on Stratigraphy (ICS), provides the fundamental framework for much geological understanding (we all know stratigraphic names like ‘Jurassic‘). It allows correlation within regions and at a global scale. The sequence of events identified using this system has allowed us to build a sophisticated (albeit incomplete) model of how Earth’s system works, and that has relevance to engineers, conservationists, businesses, politicians and everyone else.
A fundamental requirement of a new stratigraphic period (or chronostratigraphic period to be precise) is a start. Traditionally, this involves finding a distinct feature, or set of features in the rock record that can be identified at many sites around the world – i.e. its definition is reproducible. For the Anthropocene, this is taken as a global change due to the significant impact of people. What this change could be is still undecided. One possibility is the first major impact of agriculture, which led to a massive increase in soil erosion in the Neolithic. The problem here is that the Neolithic occurs at different times, and with different degrees of impact, in different places. We could take it back to the production of tools – difficult to define exactly and overlapping with existing geological periods/stages. It is also difficult to use atmospheric fallout from industrially-derived air pollution or ecological changes ans these can have very local signatures.
In the Independent article and Daniel’s blog, the proposal to set a fixed date – 1950 AD – is highlighted, with Dr Jan Zalasiewicz, chair of the Anthropocene Working Group of the International Commission on Stratigraphy (ICS) as the main proponent. The argument, based on unambigious evidence, is that there has been a distinct increase in the human impact on the global environment since the late 20th Century. Sediments from after 1950 AD frequently show changes in their physical composition compared to before. For example, beach samples around the world often show the presence of tiny plastic fragments. Atmospheric atomic bomb tests have altered the radiogenic isotope signature of the atmosphere and this has ended up being recorded in fine grained sediments – it is actually a useful way to date recent deposits.
I have some problems with using 1950 AD (or CE, depending on preference) at the moment. It is, conveniently, the date normally used as the fixed point in radiocarbon dating i.e. 1950 AD = zero 14C years before present. This is a fairly arbitrary date. If Libby had discovered the method earlier or later, it would be different. Bomb-derived radioisotopes do increase after 1950 AD, but the peak is not until 1963 AD. When this activity is examined in a sediment sequence (e.g. using 137Cs), there is sometimes a distinct peak, which can be used as a marker, and sometimes not. Sometimes, bomb-derived material moves through the sediment with groundwater movements and can preferentially accumulate at new locations. So, while we can successfully use these radioisotopes, I don’t think we can assume that the quality of the record will be good at every site around the world.
There is a more fundamental issue with using 1950 AD. If that is defined as the start of a period of distinct pollution, there is a risk that future work will assume that an increase in pollutants in the sedimentary record dates to 1950 AD. That may not necessarily be the case. Furthermore, material could be reworked, and pollutants may be remobilised. Assumptions are to be handled with caution in science, and especially geological science.
So, if 1950 is perhaps unsuitable, when should the start of the Anthropocene be set? As discussed above, the onset of agriculture is variable from place to place, as is the start of industrial activity. We could use the signal of climate change, but that will vary from site to site, depending on local environmental sensitivity – and what date would we use? Maybe another, better date can be identified but, if we are mainly talking about features formed in the historical period, maybe we should just use historical terms and chronologies? They will be more familiar to a broader audience than “The Anthropocene” I suspect – and, it is essential to remember the audience here.
In the views attributed to Professor John Burrows in Daniel’s blog, it is stated “that the Anthropocene be formalised as a geological entity to drive political action towards adapting a more sustainable future for the planet“. I think this is dangerous territory. This is not because I don’t think human impact on the global environment is not important – far from it! – but we are talking here about a revision of a globally, and hopefully impartially, used scientific system. Its revision should not be driven by a political position but by carefully and critically assessed scientific study. As soon as science starts to look political, it immediately becomes susceptible to accusations of bias and being a type of Climategate “trick” (i.e. sceptics focus on a misunderstanding of the means of communication, rather than the message itself), and that directly undermines the real message that we are significantly changing the world we live in, in many dramatic and subtle ways, and not always for the good.
Today’s sad news of possibly in excess of 350 deaths in a landslide in Badakhchân province, Afghanistan (http://www.bbc.co.uk/news/world-asia-27261783), made me wonder what landslide processes are active in the region. I couldn’t find the precise location of the village of Hobo Barik (or Aab Barik?) but did come across this interesting valley at 36 degrees 39 minutes 10 seconds N, 70 degrees 52 minutes 10 seconds E. (the image below, from Google Earth, is just over 6 km across (west to east) and reproduced with a 1:1 vertical exaggeration.
Fig 1. Badakhchân region valley. View to North.
The slope immediately to the east of the river, in the centre of the image show significant gulleying and a larger, inverted triangular area of erosion towards the top. A close up (below) shows this erosional triangle clearly. The triangle has a maximum width of about 1 km and extends from an elevation of about 2600 m down to about 2000 m over 1 km horizontal distance (the river is at about 1700 m).
Fig 2. Badakhchân region valley side. View to East. 1:1.5 vertical exaggeration
Zooming in closer to the bottom of the gulleys, there is a fan terrace extending along the bottom of the slope with some clear surface markings. The ones running left to right, a bit like contours on a map, look artificial and may be field boundaries made from stones removed from the fields to make farming easier. The darker, irregular patches running down the image are intriguing.
Fig 3. Fan terrace with depositional features
A close up of one area of these dark patches shows the best-defined to be parallel ridges, or levees. These are almost certainly debris flow lobes, suggesting that this is the most recently dominant slope process. The flow deposits extend well out on to the fan terrace, with some possibly reaching the river – a flow length of up to a kilometre.
Fig 4. Debris flow lobes on fan terrace surface
Fig 5. Debris flow deposits near river
It certainly seems that some of the gullies are, or have recently been, active. Fortunately, in this particular case, they do not appear to be a direct threat to the nearest village which is about 1.25 km on the other side of the valley. Tragically, today’s news highlights the risk faced daily by many of Afghanistan’s people.
Remembering William Smith, engineer and geologist, map maker extraodinaire
William Smith’s “A Geological Map of England and Wales and Part of Scotland” (1815) On this date, the English engineer and geologist William Smith was born. Smith was instrumental in extending the science of stratigraphy. His early work was as a miner and an engineer, for a canal-digging company. From this experience he observed the difference in rock layers. He also recognized that the same succession of fossil groups from older to younger rocks could be found in many parts of England, which he called the principle of faunal succession. He traveled the entire country to verify that relationships between the strata and their characteristics were consistent everywhere. Thus Smith created a profile of the entire country of England. His great geologic map of England and Wales (1815) set the standard for modern geologic maps. Many of the colorful names he gave to the strata are still in use today.
“Sinkholes” have been making the news quite a lot recently in the UK and elsewhere (e.g.http://news.sky.com/story/1205452/sinkhole-swallows-shocked-teenagers-car; http://www.bbc.co.uk/news/science-environment-26251220). Although not as extensive as the recent (and ongoing) flooding, the rapid collapses have been dramatic, impacting on unsuspecting homeowners and, in the case of the M2 collapse, a significant number of travellers. Quite appropriately, there has been fairly extensive media coverage and a significant number of earth science and geotechnical types (even me!) have been called upon to provide comment.
It is really important that the media have provided this coverage. These collapses present a very real risk to life, and cause untold emotional and financial distress. However, the coverage has, perhaps, been slightly skewed away from a really significant issue – the role of former landuse. There have been some excellent and clear descriptions of the natural karst processes (e.g. by the BGS’ Dr Vanessa Banks). There has been less on mines, even though some, perhaps most, of the reported sinkholes are in areas where mining is known to have occurred (try putting the various sites into http://old-maps.co.uk.
In the Chalklands of southern England, mining and quarrying has taken place for millennia. Neolithic mining has been identified at Grimes Graves, in Norfolk (well worth a visit!). Many other Chalk mines from different time periods are known (see e.g. Dr Clive Edmund’s paper ) and it is likely that many others are present but undiscovered. Some are extensive, while others are small chambers with a narrow vertical shaft. Some seem to be associated with old brick clay pits. One of these collapsed in Reading, Berkshire, in 2011 . It seems that, once mining has ceased, the shaft is plugged though the subsurface working might remain open. After a while, in some cases, the position, or even existence of the shaft is forgotten.
Subsequent construction on the site would, one would hope, include an assessment of soil stability, followed by appropriate stabilisation. It is possible that a site investigation could miss a mine shaft (possibly only a couple of metres or so across). Only at a later date does the fill of the shaft migrate downwards, sometimes by simple fall, but normally by being washed out. This can be because of a focussing of surface drainage (e.g. at a broken pipe or soakaway), or following an extended wet period (and we have just had the wettest winter for many years.
The end result of both natural or artificial cavity collapse can look very similar – and the impact on people and property can be the same, whatever collapse process is involved. There is, however a very significant point in terms of risk management, perception of risk, and responsibility which the recent media coverage underplays. A risk posed by natural processes can be perceived as something like an “Act of God“, where the likelihood of any individual or property being affected. Potentially, a natural karst collapse could happen almost anywhere in the Chalklands (I know specialists may be able to identify more likely locations but these experts are in short supply). The risk, therefore is relatively diffuse and, because . In contrast, mining collapse risk is more restricted, and is therefore theoretically predictable. As a result, the risk is geographically limited but, in specific locations, is high. The trick is to identify these high risk areas and apply appropriate mitigation techniques.