Saturday, 31 July 2010

A lot of scary amazingness

65 million years ago, a meteor at least 10-km wide impacted Mexico's Yucatan Peninsula, causing global catastrophe.  The force of the explosion was significantly bigger than any volcanic event in history and the shock waves probably triggered worldwide earthquakes, a megatsunami, a massive release of gas and dust and heating of the atmosphere which devastated the climate and caused mass extinctions, including most dinosaur species existing at that time.

The site of the impact, Chicxulub crater; is a circle 170km across, with half on the Yucatan Peninsula, and the other half in the water of the Caribbean Sea.

On land, a trough along the outer edge of the crater contains a vast semicircle of "cenotes", deep limestone sinkholes filled with fresh water.


This BBC clip explains:





Many of the cenotes are connected by an even deeper network of flooded caves which leads to the sea.  Freshwater percolating down from rain on the surface and seawater flowing in from the Caribbean form "haloclines", distinct layers of water which don't mix.  This clip shows the strange optical illusions caused at the boundary between the layers:





The first half of this clip shows another peculiar optical effect: a layer of hydrogen sulphide which appears to be the bottom of a cenote but is in fact a cloud of gas suspended deep below the surface:

2 comments:

Leigh said...

Great footage in these three clips, Grace, which I'm glad to have seen, thank you.

Grace Dalley said...

Glad you enjoyed them, Leigh. I saw the original programmes from which these clips are taken some years ago and they have stuck in my mind. In a good way. :-)