Brihadeeswarar Temple, India

Khursheed Dinshaw (India) Construction of the Brihadeeswarar Temple (also spelt Brihadisvara or Brihadeshwara), which is in Thanjavur in the state of Tamil Nadu, India, began in 1003 AD by Rajaraja I and was completed in 1010 AD. It is made of blocks of granite that were sourced from around 50km away. Almost 130,000 tonnes of granite were used to build this temple. The popular theory of how the blocks were transported is that they were gradually rolled here with the help of elephants. The design of the temple is meant to represent a cosmic structure called Mahameru, which symbolises energy from the universe, including from living as well as inanimate beings. The temple is dedicated to Lord Shiva in the form of a lingam (that is, a symbol of divine generative energy often in the form of a phallus), which is 3.66m high. The courtyard inside which the temple is built measures 240m by 120m. The Brihadeeswarar Temple, also known as the Big Temple, is an architectural marvel in stone of the Chola dynasty. It is also a UNESCO World Heritage Site. The tower, which is built over the sanctum, has a height of about 66m and has 13 storeys (Fig. 1). Fig. 1. The tower built over the sanctum has a height of 217 feet and has 13 stories. There are eight sikharas (spires), which are also made of stone and weigh about 81 tonnes. There are two circumambulatory passages. The walls of the lower passage are decorated with … Read More

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Concretions in sandstones of the Inner Hebrides, Scotland

Mark Wilkinson (UK) Concretions are a common feature in many sedimentary rocks, yet they seem sometimes to be misunderstood. So, how do concretions form? As well-studied examples, let’s look at the ones found in some of the sandstones of the Scottish Inner Hebrides, notably the islands of Eigg and Skye. The concretions are found in several formations, but perhaps the largest and most spectacular are in the Valtos Sandstone Formation of the Great Estuarine Group. This was originally named the Concretionary Sandstone Series after the prominent metre-scale concretions. It is Bathonian in age (Middle Jurassic) and is interpreted as having been deposited in a coastal environment. The Great Estuarine Group is becoming famous for its abundant dinosaur footprints and much rarer skeletal material. The concretions themselves vary from spherical to elongate volumes of rock and are typically from around 50cm to one metre or more in diameter. They are also often coalesced into groups (Fig. 1). Inside the concretions, the spaces between the sand grains are filled completely with a calcite cement. The concretions are resistant to weathering compared to the host sandstone, which is fairly soft, so stick out from the cliff in a sometimes rather alarming manner as you walk below them. I’ve been visiting the concretions sporadically for around 30 years and some of the ones that I photographed in the cliffs in the 1980s are now lying loose on the beach. None of them have fallen while I’ve been there, touch wood. Fig 1. Concretions on … Read More

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Disappearing Dunwich

Roy Bullard (UK) There are many places around the coastline of the British Isles that are quite simply majestic and, in their own unique ways, full of magic. Dunwich lies between the lovely town of Southwold and the village of Sizewell on the East Coast of England in the county of Suffolk. It is a coastal area that is easy to include in this category and is a place that I love to visit. However, as you sit there on the shore watching the cliffs and the North Sea, it is hard to imagine that so much has been lost since the time when Dunwich was once a large, thriving community. Fig. 1. Sandy cliffs of Dunwich. My aim in this short article is to take a look at the present state of this coastline and compare it with the coast as it once was before huge amounts of coastal erosion had taken place. In addition, I will take a look at the area’s history and mention, in passing, one of its well-worked, mythical tales. A steeply sloping shingle beach now lies in front of the cliffs at Dunwich. These cliffs have changed a lot over time but, over the past few years, erosion has decreased substantially. The cliffs today are overgrown and this indicates a significant slowdown in the rate of erosion. However, with the ongoing threat of climate change and rising sea levels, the local residents and council have joined together to act now to protect the northern … Read More

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Carbon Capture and Storage (CCS): Using geology to fight climate change

Mark Wilkinson (UK) Practically everyone has an opinion on climate change by now, although for the vast majority of scientists, the weight of evidence is overwhelming – emissions of carbon dioxide and other greenhouse gases are causing climate change, sometimes referred to as global warming. One possible technology for fighting climate change is Carbon Capture and Storage (CCS) in which geology plays an important role. In fact, future generations of geologists may be employed searching for CO2 storage sites in the subsurface, rather than for the more traditional search for oil and gas. The aim of CCS is simple – to allow the continuing use of fossil fuels while reducing the emissions of greenhouse gases into the atmosphere. In the long term, the burning of fossil fuels will probably cease, but until we can rely on renewable sources of energy, we are stuck with these fuels as a cheap and reliable energy source. CO2 is emitted during many activities, including driving cars and heating homes, but the largest single sources are fossil fuel power plants, which generate electricity, followed by industries, such as steel works and cement plants. It is these that most research has been focussed on. And, in principle, the technology is simple – capture the CO2 from a source (such as a power plant; Fig. 1) before it gets into the atmosphere, then transport it to a suitable storage site and inject it into the ground where it will remain for tens of thousands of years. Fig. … Read More

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Hutton’s unconformity and the birth of ‘Deep Time’

Dr Mark Wilkinson (UK) I sometimes ask a question to students in an introductory class about geology: “What is the most famous geological site in the world?” For students from the western hemisphere, the Grand Canyon in the USA is a popular choice. However, if you were to ask the same question to a group of geologists, you might get a different answer, and one option is Siccar Point on the coast some 65km southeast of Edinburgh in Scotland. Although the site itself is relatively modest, a gently sloping platform of rock partly washed by the sea at high tide, and it lacks the spectacular grandeur of the Grand Canyon, the historical significance easily outweighs the lack of scenic drama. I’ve taken several groups of visiting geologists to the site, and so far only one of them has knelt and kissed the ground, but the site could be considered to be one of the ‘holy’ sites of our science. It is difficult for most modern geologists to imagine the world when any interpretation of the geological record had to be constrained by the literal interpretation of the Bible. A particular problem is the short timescale of the account of the creation of the Earth in Genesis, and the age of the Earth as calculated by Bishop Ussher, who allowed only some 6,000 years for the whole of geological time. The person who is frequently credited with expanding geological time to the ‘deep time’ we know of today is James Hutton. … Read More

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