The phenomenon of hotspots.

 

I am just starting my A2 course in Geography and even though we are doing tectonics, (something we’ve done every year for the past 5 years) there is something that has particularly caught my attention. Hotspots. If you don’t take geography then I will explain that under the earth we stand on are big tectonic plates that move around. One is called the Eurasian plate which hosts Asia and Europe, the biggest landmass in the world (So they are pretty huge).

The main tectonic hazards are the standard, earthquakes and run of the mill volcanic eruptions that have the potential to destroy more than a series of nuclear bombs, but thankfully these are fairly predictable because they are usually found only on plate boundaries. Destructive, collision and constructive boundaries create various volcanoes and occasional earthquakes whilst conservative boundaries provide us with earthquakes. That is true with the exception of these hotspots. Hotspots are sneaky; they can appear anywhere and form spontaneous volcanoes. And no one knows exactly why. They are one powerful scientific anomaly.

To explain the wonder of these hotspots I will give you an interesting example. When we think of Hawaii we think of picturesque islands, grass skirts and amazing holidays. But have you ever sat on a beach and thought “Hey! How did this get here?” I bet you didn’t.  Or if you did, I’m sure you didn’t get it right. Hawaii is indeed the result of a hotspot. Surprise! Hawaii is, yes a series of volcanic islands, in the middle of a tectonic plate called the Pacific. Beneath Hawaii there is a plume of beyond boiling hot lava desperately trying to reach land. One idea that is pretty secure is that this plume doesn’t move. We can figure this out by the trail of volcanic islands, and although it’s easy to think the plume is moving, we have to remember that the plate is evidently moving. Imagine a hole puncher pushing down over and over and someone slowly dragging the paper through it. Hawaii is a little like that only Hawaii’s path has been made over billions of years and the materials are a little different.  However these volcanoes need maintenance to remain islands in a powerful sea, so the oldest volcanic island is now little more than a sea mount whilst new volcanoes have to build into islands.

There are several theories to explain this hotspot and the first is Wilson’s stationary hotspot theory. This presents the idea that there are spots (like sun spots under the earth) that burn hotter than other areas over long periods of time. Because of this a plume forms that is so hot, it shoots straight to the surface and pushes through to form a volcano.

The second idea is the shallow hotspot theory (This is my favourite). This theory is rather smart and directly under the Earth’s crust is a sticky layer of magma called the asthenosphere. This theory suggests that there are shallow tectonic interactions between the asthenosphere and the mantle. The idea of this is that in the distant past over the plume was the plate boundary, specifically the Pacific-Kula ridge. Because of this, the previous activities beneath this point have caused the pressure plume to continue, even though the plate boundary has moved away. Hence volcanoes continue to form over these points.

However both of these theories are highly dependent on a stationary plume, an idea that has not been proven by solid evidence. Drill samples have been collected since the 1960s however that show us how the hotspot area that created Hawaii is moving faster than the plate. These samples provide us with solid evidence that the magma plumes do in fact move an idea with enough power to throw our whole understanding of hotspots upside down. This is called the moving hotspot theory and leaves us with the solid fact: we have no idea what goes on at the centre of the Earth.