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Originally posted on Geography Directions:
By Steve Cinderby, University of York, UK, and Sue Bagwell, London Metropolitan University, UK. Globally our societies are becoming increasingly urbanised with the United Nations (UN) reporting that already the majority of people live in…
Owing to an attempted shift to more academic writing and partly in reaction to the few friends who haven’t been too thrilled with my use of this platform to rant, my posts over the past year have been fewer and less about opinion and more about experience. However, what’s the use of nurturing a blog of your own if you cannot occasionally rant!
My peeve today is, unsurprisingly, the flooding many cities across the world are experiencing and the general unpreparedness we have seen in dealing with them. Experts have attributed the higher incidents of flooding to changing patterns of precipitation (in the form of storms, rain, typhoons, cyclones), both in terms of the amount and the timing. Whether or not we link this to climate change, to me, is a moot point right now as we stare at mass destruction and anguish in Houston, eastern India, Nepal, Bangladesh and…
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Earth’s ICE RECORDSIce cores preserve climate history of million of years. Most of the ice cores are taken from the ice deposited in Antarctica and Greenland. Some interesting facts…
Ice cores have been preserved in US National Ice Core Library (NICL) in Denver Colorado.
Dust and chemicals trapped inside the ice samples can delineate the climatic conditions prevalent in the different times in the past. Climatic Histories upto 850000 years has been recreated.
How the age is determined??
Water like any other chemical contains normal oxygen 16 (O16)atom as well as a very small fraction of oxygen 18 (O18)atoms. Water evaporation is a function of temperature. At higher temperatures O18…
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Asthenosphere is zone of Earth’s mantle (upper part of the mantle)lying beneath the lithosphere and believed to be much hotter and more fluid than the lithosphere. The asthenosphere extends from about 100 km to about 700 km below Earth’s surface.
It was first named in 1914 by the British geologist J. Barrell, who divided Earth’s overall structure into three major sections: the lithosphere , or outer layer of rock-like material; the asthenosphere; and the centrosphere, or central part of the planet. The asthenosphere gets its name from the Greek word for weak, asthenis, because of the relatively fragile nature of the materials of which it is made. It lies in the upper portion of Earth’s structure traditionally known as the mantle.
Heat from deep within Earth is believed to keep the asthenosphere malleable, lubricating the undersides of Earth’s tectonic plates and allowing them to move. Convection currents generated within the asthenosphere push magma upward through volcanic vents and spreading centres to create new crust. Convection currents also stress the lithosphere above, and the cracking that often results manifests as earthquakes. According to the theory of plate tectonics, the asthenosphere is the repository for older and denser parts of the lithosphere that are dragged downward in subduction zones.
Tectonic plate interaction with the
upper layers of the Earth, USGS
Asthenosphere boundary is usually referred to as LAB. The asthenosphere is almost solid, although some of its regions could be molten (e.g., below mid-ocean ridges). The lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature. In some regions the asthenosphere could extend as deep as 700 km . It is considered the source region of mid-ocean ridge basalt (MORB).
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