 |
 The volcanoes seen from a different angle | |
| Food For Thought | |
| We live on a planet hurtling through space, spinning as it goes. Below our feet, the rocks sizzle and the intense heat turns some of them into a flowing liquid. | |
| The Outward Signs | |
| We see few signs of our frantic rush through space and we can perhaps be excused for not giving this too much thought. We notice, of course, that night changes to day and day to night, but we simply accept that, without question, as part of our normal existence. On Lanzarote, however, the dramatic effects of volcanic activity are seen everywhere - a sight unique in the world. The effects cannot be ignored. | |
| We See The Effects But What Are The Causes ? | |
| Seeing so many extinct volcanoes, one begins to wonder. Why do volcanic eruptions occur? Why on Lanzarote in particular? Will the volcanoes erupt again? If so, when? So many questions...... To get some answers, I went along to the Lanzarote Ministry of Environment's Visitor and Interpretation Centre at Mancha Blanca, close to the Timanfaya National Park (the "Fire Mountains"). This centre provides a great deal of information about the characteristics of the park. It also has a permanent exhibition with interpretative displays, a simulated eruption, a guide-interpreter service and a multimedia audio-visual programme. All this takes place in a purpose made building, designed to be in harmony with the volcanic area in which it is sited. Before going to the Visitor and Interpretation Centre, I thought of the Earth as being simply the land and sea which I see around me. Having been (and also done a little research), I now view the Earth rather differently. There is more to the Earth than it's rocky surface. So very much more !! | |
| Putting Things Into Perspective | |
| The solid rocky surface on which we live is unbelievably thin. It varies in thickness from a minimum of 3 miles (below the oceans) to a maximum of 25 miles (below the highest landmass). This surface is our home, yet it is only a very small part of the Earth. Volcanologists often liken the surface of the Earth to the skin of an apple in order to emphasise it's thinness. The likeness ends there, however. Below their surfaces the apple and the Earth are very different. | |
| The apple is solid - not so the Earth First Things First, However | |
| Our Place In The Universe | |
| Having been born from the matter contained in the universe, the Earth is now racing through space, spinning as it goes. The forces which this creates generate incredible heat and pressure at the centre. The temperature there reaches 9,000 degrees Fahrenheit and the pressure is 3 million times that which we experience here on the crusty surface. Some pressure !! It is so great that you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth !! These extremes of heat and pressure gradually - very gradually - fall until, when the surface of the Earth is reached, they are at a level which we find acceptable - and with which we can live. | |
| The Effect Of The Heat And Pressure | |
| As a consequence of the extremely high temperatures to which they are subjected throughout the greater part of the Earth, the elements found there (metals of various kinds) are in the form of liquids. For the first 800 hundred miles radiating out from the centre, the pressure prevents the liquid from moving around and it acts like a solid. For the following 1,400 miles (to just over halfway to the surface), the Earth is composed of iron and nickel in liquid form. | |
| The Crust Begins To Form | |
| Still just over 1,800 miles to go, but we are now approaching that part of the Earth which is the most important for us. From here to the solid, rocky surface, the liquid is becoming something in the nature of a 'hotpot' (in cookery terms). Some of the molten rock begins to solidify at the temperatures experienced here - somewhere not so far below our surface homeland. The crust on the 'hotpot' begins to form !. Whilst some of the molten rock is beginning to solidify, the rest remains in liquid form. The rock which remains molten is as buoyant as a cork. Being buoyant and lighter than the surrounding solid rock, it rises. | |
| Pressure Now Becomes An Important Factor | |
The expansion of the gases drives the molten rock towards the surface. It seeks a way out through the weakest points in the surface crust (the crust of our 'hotpot'). The effect which a reduction in pressure has on a gas can be illustrated with a bottle of fizzy lemonade (or the bottles of champagne which sportsmen are so fond of shaking when they achieve success!). If you place your thumb over the top, shake it vigorously and then suddenly remove your thumb, there will be a mini-explotion of the gas contained within it. The expanding gases can make their way out of the molten rock quietly or explosively. The governing factor is the heat and fluidity of the liquid. If the molten rock is superhot and is therefore a thin liquid, the gases make their escape without much trouble. If it is less hot and therefore thicker, the gases explode outwards through the surface. Volcanic Eruptions Are A Good Thing ! No, it's not a joke - they really are. They are nature's safety valve (in the same way that the pressure release valve on a pressure cooker prevents the whole of the cooker from exploding). Of course, you may not think they are such a good thing if you are in the wrong place at the time ! If there were no way of relieving the pressure which builds up just below the surface, much of our crusty surface might blow off ! | |
| The Weakest Points In The Crusty Surface | |
| Volcanic eruptions occur only in certain places and do not occur randomly. Our crusty surface is not one single solid crust, but consists of 12 separate pieces. These pieces are always on the move. They spread apart, collide, slide past each other and even slide over each other. The volcanoes occur most frequently where the pieces meet. The emerging molten rock seeks out these weak points. Our particular interest is in two pieces of the crust which meet in the middle of the Atlantic Ocean. Here, the molten rock is constantly bubbling up between the pieces, adding more solid rock to our crust. | |
| Hot Spots | |
| The molten rock making it's way to the surface is not all at the same temperature. In some places the liquid is especially hot. These 'hot spots' often occur at the places where the pieces of the crust meet, but they can also cause volcanic eruptions within a piece of the crust. | |
| The Birth Of Lanzarote | |
| As we have seen, two pieces of our crusty surface meet under the Atlantic Ocean, between the American and African continents. There is one particularly 'hot spot' where these meet and it was here, 20 million years ago that Lanzarote was born. | |
| The Birth Of The Other Canary Islands | |
| In those places where pieces of the crust meet, new rock is being added to the crust at the rate of 2 or 3 centimetres a year. No big deal !! After a few million years, however, even at this rate, many tens of miles had been added to the crust where Lanzarote was born. Lanzarote was no longer on the edge. Then (where Lanzarote had been born) up came, successively, the other islands - later to become known as the Canary Islands. | |
| The Volcanic Eruptions Of The 18th And 19th Century | |
| We have seen how the Canary Islands came into being, but one thing remains unexplained - the reason for the Lanzarote eruptions of the 18th and 19th century. Was Lanzarote, although no longer on the edge of a piece of the crust, again over another 'hot spot' ? I have seen no other explanation. | |
| Unfortunate For Some | |
| Volcanic activity is, apparently, a good thing in that it releases the pressure building up below our crust. It was very unfortunate, however, for those living in Lanzarote in the 1730's. No lives were lost, but the eruptions went on for six years. It must have been like living in a war zone. At the start of the eruptions, an estimated 5,000 people were living here. The best known historical record of the events is the diary written by the parish priest of Yaiza, Don Andrés Lorenzo Curbelo. This provides an account of events from the beginning of the eruptions until, rather than stay and put up with the risk of continued eruptions, the inhabitants of the area finally fled in 1731 and 1732. | |
| Are All Those Volcanoes Really Extinct ? | |
| One can never be sure........................!!?? |
