Hot Spots Unplugged

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Article Review – Hot Spots Unplugged
Tarduno discusses the geological phenomena of 'hot spots' – areas where the earth's core is hot enough to burn through the crust, driving lava to the surface to form new land masses (89). The article covers the research that shaped our understanding on this theme during the 20th Century, identifying a largely submerged chain of mountains in the Pacific Ocean, known as the 'Emperor Seamounts', as a key point of reference from which numerous landmark theories have drawn their evidence. The main point of contention is whether or not hot spots are a static presence beneath the earth's crust (89).

The prevailing view on hot spots is that they are fixed points, rooted deep within the earth's core, and that chains of mountains and islands such as the Emperor Seamounts are formed as the tectonic plates which form the earth's crust move across the hot spot. This theory would imply that the Pacific plate has moved north and, more recently, north east. The Emperor Seamounts demonstrate this trajectory, with the youngest of its formations being at the south western tip of the range around Hawaii (89). Tarduno argues that hot spots are not static, but move around with currents in the mantle (89).

To prove this theory, Tarduno uses core rock samples from the ocean floor around the Emperor Seamounts. These samples are collected using a pipe drill mounted on a research ship and are analysed to reveal information relating to the date and location of their formation.

The previously accepted view that hot spots don't move would imply that the entirety of the Emperor Seamount chain was formed at a tropical latitude around the location of Hawaii, and that tectonic movement has carried this chain of mountains and islands in a north easterly direction over tens of millions of years (90). Any indication that rock formation occurred at a different latitude would imply that hot spots are not fixed in place.

The magnetization of minerals within rock samples is important as this is set as lava cools, and so acts as a determinant for the date and location of formation. The polar magnetization of these minerals gives us an idea as to when the rocks were formed as it can be matched to historic cycles of polarity, whilst the magnetic inclination of these minerals is directly linked to the latitude at which they were formed. Analysis of fossil content is used to ratify age, whilst the presence of coral debris corroborates assumptions about the location of formation, as this is associated with rocks formed at tropical latitudes (90). Magnetometers are used to record the magnetic evidence, with results being presented graphically through the use of 3D modelling (90, 92). The results of this analysis prove that formations in the northern region of the Emperor Seamounts were formed at more northerly latitudes than the current location of the hot spot beneath Hawaii, indicating that the hot spot has in fact moved.

For many years hot spots have been viewed as fixed anchor points against which historic movement of continental plates can be tracked. In particular, theories relating to 'polar wander' – the extent to which the earth's surface deviates from the spin access over time – are founded upon assumptions of hot spot fixity (93). Traduno's conclusion that hot spots move invalidates the outcomes from research on polar wander, which must be revisited to account for hot spot movement.

Works Cited
Tarduno, John A. “Hot Spots Unplugged.” Scientific American. January 2008, pp. 88-93