Tuesday 28 February 2012

Extensional grabens in our shrinking Moon

The largest of the observed grabens with the
 Narrow Angle Camera (NAC) of the LRO spacecraft. 
It is about 500 m wide, and nearly 20 m deep. 
(Credit: NASA/Goddard /
 Arizona State University/Smithsonian Institution)
Who has not read a thousand times that our Moon is a death body without any activity? Well, it turns to be the opposite: The Moon has been active at least until very recent times, and very likely this activity continues now.

Lunar Reconnaissance Orbiter (LRO) spacecraft has obtained images of the surface of our satellite where extensional faults are clearly visible. NASA estimates that this faults are not older than 150 million years, which is pretty young for what we expected to be the lunar tectonics.

Two years ago, the Lunar Reconnaissance Orbiter mission also detected other young geological features, which where interpretd as compressional uplifts. It was said, at that time, that the Moon is shriking. But the identification of extensional faults shows that this shrinking (due to thermal contractions) is not homogeneus everywhere.

But why not listening directly to Tom Watters from the Smithsonian Institution? (You can also active the subtitles!):

Diagram of formation of a graben with two bounding faults (Credit: Arizona State University/Smithsonian Institution)

Read more here: http://www.nasa.gov/mission_pages/LRO/news/lunar-graben.html

Thursday 23 February 2012

The origins of plate tectonics, with Dan McKenzie and Fred Vine

The Geological Society of London opened a few months ago a channel in YouTube with the aim of reaching a larger audience through divulgation videos.

Yesterday, The Geological Society uploaded a very interesting inteview to Dan McKenzie and Fred Vine, where they discuss the early history of development of the theory of plate tectonics. The clip is taken from 'Dan McKenzie and friends: highlights from the Bullard labs'. [Copyright: 2011 Cambridge University (Depart. of Earth Sciences)].

Enjoy it!


Tuesday 21 February 2012

Structural Geology Lab Manual by David Allison

A structural geology laboratory manual comes always handy to anyone dealing with maps, cross-sections or stereograhic nets. Even those experienced geologists who have left their university days left behind the mist of time need to have one. Many techniques are learnt, but soon leave room in our room for other issues that may be even more important (e.g. telephone number of the canteen waitress, local pubs near an outcrop, and so forth...)

There are methods in structural geology that if one doesn't use them regularly, soon become rusty and we simply need to refresh them from time to time: how to rotate lines and planes with a stereonet, how to solve a three-point problem, etc.

Today I'd like to present you an excellent structural geology lab manual, written by David T. Allison, an associate professor of geology of the Department of Geology and Geography of the University of South Alabama:


The manual contains explanations and exercises on attitude measurements, true and apparent dips, three-point problems, stereographic projections, rotations with the stereonet, stereograms, geologic mapping and cross-section construction, thickness and outcrop problems ans statistical techniques.
It is written in a very approachable style, and completed with good figures that will help anyone to understand and practise the foundations of our profession or studies.

The text makes reference to several spreadsheets that you can find in the homepage of the author:


 I hope you find it useful. Comments are welcomed, as usual!