The interesting graphic below was tweeted by @simongerman600. Interesting how big a slice is devoted to the ubiquitous I Phone. Useful discussion starter of lessons on TNCs, use of rare earth resources etc.
Its favourite rock time again! Last month, I wrote a blog entry about the Saunton granite erratic. Just a little further along the north Devon coast is another glacial erratic – this time at Baggy Point in Croyde Bay.
The rock in question is a large granulite gneiss boulder that has been carried from Western Scotland. It weighs some 50 tons, but sea erosion and encrusted lichens make it a little tricky to spot.
A glacial erratic is a rock that has been transported from its original site by ice and deposited somewhere else, where it bears no connection to the local geology. The Baggy boulder is one of a suite of over twenty glacial erratics that can be found along this stretch of north Devon coastline. Two of them are quite accessible (this one at Baggy Point, and another at Saunton described in a previous blog) and are relatively easy to identify, but most of the others are much smaller and quite difficult to find.
As at Saunton (see previous blog), the Baggy erratic sits on a wave cut platform created from the local rocks. At this location, the foreshore consists of Baggy sandstones that overlie the Upcott slates that form Baggy Point itself. These sedimentary beds of mudstones, siltstones and sandstones were formed in the Devonian Period between 359 to 372 million years ago. They were deposited as horizontal layers on the sea bed, but have since been uplifted and contorted, and hardened into vertically aligned layers. The sea has since carved this rock into sharp ridges and ancient fault lines are marked by long, straight and deep gullies, created where less-resistant beds have been eroded at a faster rate.
Behind the erratic boulder is a clear exposure of an old cliff line formed from Pleistocene raised beach material, or sand rock, that was created in the Ipswichian interglacial. This provides clear evidence of how sea levels at this location have been at different heights in the past.
The upper section of the cliffs contains a loose matrix of angular rock fragments of varying size. Such deposits are known locally as ‘head’. This part of the cliff profile was created by the down-slope flow of saturated sub-soil – a process known as solifluction. Mass movement like this is associated with colder spells, particularly in the coldest parts of the last Ice Age that took place some 180,000 years ago. North Devon was then a periglacial tundra-like wilderness with mean average temperatures about 10 degrees Celsius colder than today. The ground would have been permanently frozen (permafrost), and only the top metre or so briefly melted to create an unstable slurry that flowed easily on the permanently frozen ground below. Frost shattering in the cold spells detached fresh rock fragments to feed the flow.
There remains considerable debate about how the Baggy Point erratic arrived in north Devon. it was certainly transported by ice, but there is disagreement about what form the ice took. One theory suggests that the boulder was carried here by the ice sheets from the Anglian Glaciation, the last to affect this area. Alternatively, the boulder was a dropstone carried to its present location by a grand iceberg.
Ice ages have been one of the main reasons why sea levels have changed in our geological history. During the last 2 million years or so (the Quaternary Period), ice ages have come and gone roughly every 100,000 years. As the ice caps trapped water from the oceans, world sea levels fell between 100 and 200 metres. At the peak of the last ice age (about 18,000 years ago) a Paleolithic hunter stood on the cliffs at Croyde would not have been able to see the ocean, as it would have retreated beyond the horizon. During the warmer inter-glacial periods, sea levels rose again – perhaps even reaching higher than their position today. Of course, today we also have to consider the additional cause of rising sea levels due to anthropogenic causes.
The old cliff-line was created in interglacial periods when the world was warmer and sea levels higher. Combined with a general eustatic uplift, it has been raised some 40 feet or so above the present sea level. During the ice age, sea levels fell. Since the end of the last glacial period, sea levels have started to rise again, and the cliffs are currently retreating quickly.
The Baggy Point erratic is not easily accessible, as it sits on the foreshore, well below the level of the coastal path at the top of the cliff. To reach it requires a steep descent onto the foreshore and then a bit of clambering over loose rocks, gullies, and steep ridges. Bear in mind that the erratic is not accessible at high tides, so make sure you check local tide tables and visit the site at low tide so you have plenty of time to explore.
HOW DO I FIND THE ERRATIC?
To find the erratic, follow the coast path signed to Baggy Point, accessed by turning right out of the National Trust car park at the head of Croyde beach. When you reach the white house built in a modern architectural style, look for a single wooden bench at the edge of the cliffs. A route leads to it from the main path, and to the left of the bench is a steep washed-out channel that will give you access to the wave cut platform below. Turn right, and edge your way along the base of the cliffs, over the ridges and gullies cut in the Baggy sandstone platform, until you reach the erratic.
If you decide to extend your visit with a stroll along the cliff path to Baggy Point itself, you will be well-rewarded. This walk is described in a later blog entry, and includes an opportunity to examine another erratic that can be located close to the path on the way to Putsborough.
There has been some really nice autumn weather to enjoy this week, so I decided to take a trip to Saunton beach to visit one of my favourite rocks.
Is it acceptable to have favourite rocks? My wife is not so sure, but I think it’s OK.
There has been quite a bit of cliff collapse at Saunton in recent times, and I wanted to check that my favourite rock was still visible and accessible, and not covered up by recent cliff falls.
Luckily, my favourite rock is still there – and can remain a star feature of my guided walks and fieldtrips, at least for a while to come.
The rock in question is a large pink granite boulder – an example of an erratic. An erratic is a boulder or fragment of rock that has been carried from its original site by ice and deposited somewhere else, where it bears no connection to the local geology. It is clear – even to the common observer – that this boulder is not part of the local Pilton Shales it stands upon.
The Saunton erratic is a pink porphorytic micro-granite, that originates from Gruinard Bay, Wester Ross, in the north western highlands of Scotland. Its weight has been estimated at between 10 and 12 tons, and is embedded in the base of the cliff line. It sits on a wave cut platform of the Devonian aged Pilton shale beds. it is sealed in place by the stratified ‘sand rock’ of Pleistocene raised beach deposits created in the Ipswichian interglacial that now form the current cliffs. The erratic must have arrived in this position after the shore platform of the Pilton Shales was cut, but before the sand rock that was subsequently laid down above it.
The Pilton shales beds that form the wave cut platform were created around 365 million years ago in the Devonian period. They were once soft muds and sands, laid horizontally on the sea bed. They have since been compressed and hardened and then severely folded, uplifted and contorted to now stand close to vertical. The sea has since carved this rock into sharp ridges, and ancient fault lines are marked by long, straight and deep gullies, created where less-resistant beds have been eroded at a faster rate. The shore platform has a number of steps or different levels that can be identified, according to past changes in sea levels. If you look closely and hunt around, you might be able to find some crinoids (fossilised sea lilies) in the shale beds. These Devonian beds extend underneath the sand rock cliffs before rising steeply along the line of the coast road at the top. They can be seen in numerous cuttings and quarries along the roadside.
The sand rock that surrounds the erratic are part of a raised beach that demonstrates how sea levels in this location have been at different heights in the past. The old cliff-line – now high above the present one at the level of the coast road – was created in interglacial periods when the world was warmer and sea levels higher. Combined with a general eustatic uplift, it is raised some 40 feet or so above the present sea level. During the ice age, sea levels fell. Since the end of the last glacial period, sea levels have started to rise again, and the cliffs are currently retreating quickly.
Ice ages have been one of the main reasons why sea levels have changed in our geological history. During the last 2 million years or so (the Quaternary Period), ice ages have come and gone roughly every 100,000 years. As the ice caps trapped water from the oceans, world sea levels fell between 100 and 200 metres. At the peak of the last ice age (about 18,000 years ago) a Palaeolithic hunter stood on the cliffs at Saunton would not have been able to see the ocean, as it would have retreated beyond the horizon. During the warmer inter-glacial periods, sea levels rose again – perhaps even reaching higher than their position today. Of course, today we also have to consider the additional cause of rising sea levels due to anthropogenic causes.
At this location, it is possible to identify a clear unconformity where the heavily folded and faulted Devonian age Pilton shales are overlaid by Quaternary sandstones. An unconformity occurs where two adjacent rocks were not formed one after the other in the Earth’s geological history. Here, the Devonian age rocks (named after the county where these rocks are common) were laid down between 416 – 359 million years ago, while the Quaternary deposits were started only about 2.6 million years ago.
There is a lot of debris surrounding the erratic resulting from recent cliff collapse. High tides bring the sea right up to the base of the cliffs at this location, and clear undercutting is evident all around the granite boulder. It is quite possible that if erosion at this site continues, the pink granite boulder may become lost beneath chunks of fallen sand rock.
There are a number of small caves in the Saunton cliffs, the result of differential erosion due to the differing resistance of the cemented beds.
Shingle beds and limestone beds (only 1 to cm wide) can also be identified in places in the sand rock if you look really closely. Also, at the base of the cliffs is an indication of an earlier beach level, now 5 cm above current level. Fossilised acorn barnacles can be found in the sand rock here, and these of course spend their lives below low water.
It is also possible to identify examples of cross-bedding in the sand rock cliffs. Here, the sand has been sorted by flow – with both wind and water helping to create the cross stratification.
The upper cliffs contain a loose matrix of angular rock fragments of varying size. Such deposits are known locally as ‘head’, a farmer’s term for deep rubbly subsoil. This part of the cliff profile was created by the slow down-slope flow of saturated sub-soil – a process known as solifluction. Mass movement like this is particularly active in periglacial environments. In the coldest parts of the last Ice Age that took place some 180,000 years ago, North Devon was a tundra-like wilderness with mean average temperatures about 10 degrees Celsius colder than today. The ground would have been permanently frozen (permafrost), and only the top metre or so briefly melted in the spring to create an unstable slurry that flowed easily on the permanently frozen ground below. Frost shattering in the cold spells detached fresh rock fragments to feed the flow.
So, how did the erratic get to Saunton? It was certainly transported by ice, but there is some debate about what form the ice took. One theory suggests that the boulder was carried here by the ice sheets from the Anglian Glaciation, the last to affect this area. Alternatively, the boulder was a dropstone carried to its present location by a grand iceberg.
The Saunton erratic is easily accessible, although it does involve a bit of clambering over the steep ridges of the wave cut platform at the north end of the beach. It can be found embedded in the base of the cliffs around 200 metres to the west (towards the sea) of the white buildings of the Saunton Sands Hotel that stands on the top of the cliffs. You can use your smart phone to help you find it – the screen shot and grid reference below comes from the OS Maps app:
Grid reference: SS 4402837875
Alternatively, the image below shows the What3Words code from the What3Words location app:
Bear in mind that the erratic is not accessible at high tides, so make sure you check local tide tables and visit the site at low tide so you have plenty of time to explore.
The Saunton example is one of a suite of over twenty glacial erratics that can be found along this stretch of north Devon coastline. A number of these are located on the foreshore at Saunton, but they are quite difficult to find, as the sea has disguised their form, and in some places thy have been covered up with eroded debris.
There are other impressive erratics further along the coast that are easy to find, and I will write a blog about these in the near future. To finish, here is another of my favourite rocks – the large erratic at Baggy Point, Croyde:
Web link: https://siluet.co/
This company produce wonderful city skyline silhouettes made from high quality acrylic. They are laser-cut, revealing great detail, and are produced in both glossy and matt finishes.
City silhouettes are available for a number of cities in the UK, and also for major cities across the world. Two different sizes are available – large versions are 100 cm x 14.3 cm, and medium versions are 60 cm x 8.5 cm. Extra large silhouettes are available on request.
Here are some samples from the web site, but check it out for yourself, there is lots to see!
A number of years ago, when I was a good deal less risk-averse and also rather more bendy, I took a microlite flight over Victoria Falls.
A recent news article brought back good memories of this exciting adventure, while at the same time offering an idea for a new ‘hook’ for lessons about climate change. It was part of a series examining the ways the planet is changing against a backdrop of a warming world, and described the effects of global warming on one of the world’s most recognisable landmarks, causing it to dry up.
Before and after photos Reuters
Victoria Falls is one of the natural wonders of the world, formed as the Zambezi River plunges into a chasm known as the First Gorge, forming the border between Zambia and Zimbabwe. It spans 1.7 km at its widest point, and with a height of more than 100m, it generates mists that can be seen from more than a dozen miles away, which is why locals refer to Africa’s greatest waterfall as “Mosi-oa-Tunya” or “the smoke that thunders”.
However, in 2019, Victoria Falls was silenced. In a drought described as the worst in a century, the flow of the Zambezi was reduced to a relative trickle and the Falls ran dry. Extreme swings in rainfall brought on by climate change threaten its future. Victoria Falls is getting drier and hotter. While the region still sees roughly the same annual rainfall, those rains are compressed into a smaller period of time. Temperatures are rising – average daily high temperatures in October have warmed by nearly 4 degrees Celsius from 1976 to 2017.
This extreme weather threatens not only the majesty of the Falls, but the health of the local ecosystems. The mists of Victoria Falls sustain a rain forest- like ecosystem adjacent to the falls and on the opposite cliff that faces them like a dried-up mirror image, thick with mahogany, fig, palm, and other species of vegetation. National Parks of both Zambia and Zimbabwe exist on either side of the Zambezi. The gorges and cliffs below the falls in these parks are prime territory for raptors, including falcons and black eagles.
The local economy has also been seriously affected. As one of the region’s biggest attractions for tourists, Victoria Falls is a valuable source of income for the local population, and as news of the low waters spread, traders noticed a visible drop in tourist numbers.
As well as hitting local economies, the drought has also affected electricity supplies, which are dependent on hydroelectric generation. More widely across the region, agencies reported an increase in the need for food aid, as crops failed in the drought.
Zambia’s President, Edgar Lungu – speaking at the time – called it “a stark reminder of what climate change is doing to our environment”. Observers of weather patterns in the Zambezi Basin believe the changing climate is resulting in a delay to the monsoon season, concentrating the rains into bigger, more intense events. This makes the storage of the water in the region more difficult, and makes the impact of the extended dry season more damaging to people and the environment.
The events at Victoria Falls reflect the problems being faced by Africa as a continent under serious threat from climate change. The United Nations State of the Climate in Africa in 2019 report painted a worrying picture of a continent that could see its population double over the coming century, hitting the most vulnerable people the hardest. Africa is set to be the continent hardest hit by climate change, but with the lowest capacity to adapt to these changes. We will be hearing more in future years of the issues of food insecurity, population displacement, water supplies, drought and floods.
Time magazine has revealed its annual list of the ‘World’s Greatest Places’. This includes countries, regions, cities and towns nominated by the Time Magazine network of correspondents and contributors – with an eye to offering new and exciting experiences.
The list contains 100 unique destinations, from the idyllic Portuguese town of Arouca, now home to the world’s longest pedestrian suspension bridge, to the continent of Antarctica, which this December will experience a rare total solar eclipse. And while it may not be possible to safely visit each place just yet, they’re all well worth reading (and dreaming) about until it’s time, once again, to explore.
Check out the full collection – in an easily navigable list – at:
Have you tried the USGS memory game with remote sensing images? Hours of innocent fun! Makes a nice starter for a lesson.
The Remote Sensing Imagery Game uses satellite images to familiarize students with geographic features of selected locations on Earth. The goal of the game is to introduce concepts of land type and land cover changes over time.
The objective of the game is to match all image pairs in the shortest amount of time. Images are laid out in a grid system facing down with the Earth logo on top. You can choose to pair up from just 4 images, or go for 6, 8,10, 12 and even 14 images.
At the beginning of each round, the player will click an Earth logo to reveal its image. To find its match click another Earth logo. If the two images match, they will stay face-up. If not, the cards will turn back over.
By clicking on the image a pop-up will show the area changed over time. A click on the pop-up reveals information about the image’s location on Earth, and its geographical features.
Interesting infographic from the INews newspaper that may be of use in the classroom:
Check out this great visual story.
This interactive map of the UK has the name of different towns replaced by their most famous residents – the most ‘Wikipedia’ed’ resident: people born in, lived in, or connected to a place.
Here is a section from my local area – who knew the quiz ‘Chaser’ Mark Labbett hailed from Tiverton in Devon? Who are the famous residents in your local area?