Down to Earth Extra - June 2020

DOWN TO EARTH EXTRA - June 2020

The latest edition is available HERE. 

Or you can read it below.

Strong Poison - in the well

Strong Poison - in the Well

I came across Lord Peter Wimsey and arsenic in Dorothy L. Sayers novel "Strong Poison" which I strongly recommend - the novel, not the arsenic. THIS ARTICLE is much less entertaining but very informative. 

What started as a good thing became a tragedy. Providing water from drilled wells stopped people becoming ill from gastro-intestinal infections. But, over time, signs of arsenicosis appeared. 

Why arsenic got into the water is far from obvious. The article explains the complex chemistry involved - goethite (containing Fe-3 and other stuff including arsenic) in reducing conditions breaks down to Fe-2 and releases its arsenic. Fascinating and deadly chemistry!

Well worth reading and here is a map showing where it is not safe to drink the well water.

Modelled global probability of arsenic concentration in groundwater exceeding 10 μg l-1. Click to display a larger map in a separate browser tab. (credit: Podgorski & Berg; Fig 2A, with enhanced colour)

Mary Anning - her story in an unusual form

Mary Anning - Her Story in an Unusual Form

I came across THIS and thought most of you would like it. Turn up your loudspeakers

Edenville Dam Breach

Edenville Dam Breach

One of my favourite blogs (The Landslide Blog) has 3 very interesting articles about the the breaching of this dam in Michigan USA.

The FIRST gives the news and the information that its licence had been withdrawn.

The SECOND has a video showing the failure of the dam. It is this which drew my attention.

And the THIRD discusses what happened and the consequences. The author suggest many similar dams will need to be looked at as global warming is changing weather patterns and higher rainfall may be greater than many dams can cope with. 

Martian Mud Flows

Martian Mud Flows

There are features on Mars that could be mud flows or lava flows. Until this is settled, perhaps (but unlikely) by a geologist with a hammer, speculation continues. And to provide some facts for the speculation we have THIS ARTICLE (brought to my attention by a correspondent) which describes experiments which look at how mud acts in a Martian environment.

In the low pressure of Mars's atmosphere mud acts like pahoehoe lava and looks like it also.

The initial article can be found HERE.

A suggested mud flow on Mars spied from orbit. A geologist on the ground could tell for sure.

Has Metamorphism Always been the Same?

Has Metamorphism Always been the Same?

THIS VERY INTERESTING ARTICLE follows the debate whether metamorphism has always been the same. The minerals in a metamorphic rock can tell you its temperature and pressure history. 

It has long been suspected that the average T/P conditions revealed by metamorphic rocks have varied over geological time, this article discusses A RECENT PAPER which tries to put some numbers to this speculation. And also A DISCUSSION of the paper.

At the heart of the discussion is thermobarometric data - derived from mineral assemblages which indicate the temperature and pressure at which they were formed. The 564 data points are, as one would expect, not evenly scattered through time. And clusters of data points show a wide scatter of T/P. 

But the original authors manage to extract a smooth curve showing that T/P lowered with time and suggest this is linked to the development of modern plate tectonics. 

The author of the discussion thinks the lowering of P/T is due to a fall in mantle temperature. 

All this is far above my competence - I leave you to read the articles and decide for yourselves!

The latest division in pressure-temperature space of different styles of metamorphism (colours) and the main mineral equilibria (dashed lines) that define them. Note the three T/P lines. Did early rocks follow the 30℃/km line and later ones the 10℃/km line? - very roughly speaking and using averages and with all sorts of caveats!

Peter Cawood’s ‘take’ on the relationship between tectonic development and other important variables in the Earth-system with the estimate by Brown et al. of the mean metamorphic T/P (‘thermobaric’) variation through Earth history

Footnotes May 2020

Footnotes May 2020

Footnotes, the newsletter of the Wessex Branch of the Open University Geological Society, is available for download HERE.

Remember

And, keeping the correct distance apart, read it below!

Stonechat Magazine

Stonechat Magazine

A correspondent has brought this magazine of the Horsham Geological Field Club to my notice and now I bring it to yours! 

If I edited a magazine as good as this I would be very proud! Read it and Marvel!

You can get it HERE. Or read it below.