Monday, March 30, 2020

An Outing With William Smith

I have started reading Roger Osbourne's The Floating Egg: Episodes in the Making of Geology.

It tells stories set mostly in the 1800's from the Yorkshire region of England of people involved in exploring landscapes, discovering fossils, and slowly constructing a systematic science of geology. The story of James Hutton's insight that the earth was really old based on his observation of the juxtaposition of two sets of strata at Siccar Point on the east coast of Scotland is well known. From that he deduced that the lower set of strata were deposited first, then tilted and eroded, upon which the upper set of strata were deposited. This meant that a vast amount of time separated these events.

In the late 1790's England, the need to transport coal from mines to industry led to a surge in canal building, as transport by barges was cheaper. William Smith was one surveyor in much demand. He began observing consistent patterns of rock and fossil associations through his explorations and realized that he could use these patterns to predict the presence or absence of certain rock types or fossils deep underground, even if the complete association of rocks was not exposed at the surface. Smith went on to make the first detailed geologic map of Britain, a tale best read in Simon Winchester's The Map That Changed The World.

Roger Osbourne imagines a conversation William Smith has with a fellow traveler, a Mr. Palmer of Somerset Canal Company, while on survey near the city of York. Mr Palmer is the narrator.

They climb a high tower which affords a view of the surrounding countryside. William Smith's eyes light up when he sees a line of hills in a distance.

'You are a coal mining man, Mr. Palmer, and for that you have my respect. Now if you were to go to those chalk hills and dig for coal, you would never find it. Never'

Though I had believed I understood Smith's explanations,this seemed a truly fantastic inference.

'But how can you know that Mr. Smith?  Those hills are more that twenty miles away'

'Think on it Mr. Palmer, think on it. You would need to dig through chalk,which is perhaps 500 feet thick, then through shale, limestones and red sand before you even got to the coal measures. You would be miles under the earth'.  He laughed at the thought of it.

'Can this be true?' I asked.

He turned to me, his face and eyes set strangely with a conviction that I had never seen on any man.

'Not "Can it be true?" Mr Palmer. It must be true. These are the laws of nature. They have no variance. What I seek is a philosophy which will embrace the whole earth. It cannot allow any exception'. 

The year is 1794. William Smith was optimizing mineral exploration strategy based on his new found understanding that the package of coal overlain by red sand, overlain by limestone then shale and then chalk will occur unvarying in this region.

A thousand such observations followed by countless inferences ultimately coalesced in to a rigorous science of geological mapping.

This is a lovely book.

Friday, March 20, 2020

Review Papers: Geodynamical Evolution Of India

Episodes, Journal of International Geoscience, has an open access special issue on the geology of the Indian subcontinent.

Excellent source for teachers, researchers, and curious science lovers.

I liked the paper on Deccan Volcanism a lot, especially the emphasis and attention given to the physical properties of the lava flows, and the problems of correlating (establishing their genetic and temporal relationships) lava sections from different parts of the Deccan Volcanic Province.

I don't know much about the Archean to Neoproterozoic age ( > 2500- 542 million years old)  southern granulite terrain, a region where very high temperature high pressure rocks known as granulites and charnockites are exposed. That is a topic I am looking forward to reading and learning about. The famous Anamudi Peak in the Western Ghats  are made up of these rocks. Geologists suspect that their high altitude is partly a result of differential erosion. Charnockites in particular are harder and have resisted being worn down, resulting in them standing out as high domes.

Another cool paper is on the role of microbial colonies on sedimentation patterns in the Proterozoic sedimentary basins of India (2500-542 million years ago). Microbial colonies grew as mats covering sediment surfaces influencing their accumulation and erosional patterns. Such environments became rare since Cambrian times (542 million years ago) when animals which eat and disrupt microbial colonies evolved.

Dive in.

Friday, March 13, 2020

Palghar Earthquake Swarm

My article on Palghar's mystery earthquakes has been published in The Wire Science. The article is an explanation of a recent paper that was published in the journal Tectonophysics. It favors the view that groundwater circulation is causing slippage along faults. According to the scientists involved the earthquakes are due to these very local processes.

One important point is that a link between groundwater and these tremors, even if it does exist here, represents a tipping point in a longer buildup of stress due to tectonic forces. The western margin of India is riddled by large fracture zones and faults. These structures haven't formed by groundwater movement. They are a legacy of earlier and ongoing crustal deformation due to regional and continent wide geological forces.  Groundwater flow or a build up of pore pressure cannot by itself generate enough stress to develop a fault de novo.

Dhundhalwadi is experiencing what is known as an earthquake swarm, a sequence of seismic activity with no clear peak (mainshock), and which is localised to one area. A recent study by researchers around India, including the National Institute of Seismology, has found one potential explanation for the swarm that draws a link between the monsoons, groundwater circulation and rock deformation...

Read more here.