Endogenic and Tectonic Disasters
Endogenic is a geologic term describing internal processes of the earth, such as, the operation of plate tectonics. Tectonic disasters therefore, relate to the same phenomena, referring to disasters that occur due to the tectonic activities of the continental plates, which manifest themselves in earthquakes and volcanic eruptions.
An earthquake is a perceptible vibration of the surface of the earth. The crust of the earth, the lithosphere, is a patchwork of continental plates, that slowly, and constantly move in diverse directions, shoving against one another. When the tensions in the plates, deriving from the movement and shoving, exceed the strength of the crust, an earthquake occurs. These “tectonic” earthquakes are the most frequent and strongest, but they can also derive from volcanic eruptions or mining activities.
Volcanism describes geological activities that are connected with the rising of magma from the mantle of the earth up to the surface. Volcanoes can evolve at the collision lines of the continental plates, oceanic trenches, on mid-ocean ridges and at so called hot spots – irregular formations in the crust underneath the continental plates. Volcanic eruption material can be solid, liquid or gaseous.
The most popular form of volcanoes are shield volcanoes, that erupt extremely hot, pure, liquid lava. As it flows with great speed (60 km/h), it leaves a large area covered with a huge flat shield.
Stratovolcanoes erupt all kinds of volcanic material. The magma of stratovolcanoes derives from upper layers of the mantle, from the bottom of the crust, and from an upper layer of the interior and contains more gas, therefore different kinds of volcanic material erupt in phases of explosions of solid material, ashes, lava and gases.
Earthquakes and volcanic eruptions can also trigger other disasters such as, tsunamis, volcanic winters, glacial lake outburst floods (Icelandic: “Jökulhlaup”) or Lahars.
Tremendous volcanic eruptions can burst huge amounts of ashes into the atmosphere which can shield the earth from the radiation of the sun and as a consequence diminish the earth’s temperature or the average temperature on earth for some amount of time. For example, the outbreak of Mount Tambora in Indonesia in 1815, caused the “year without a summer”, frost and snow in the summer in England and the USA, harvest failures, famines and emigration waves resulted until 1819.
In 1991, the eruption of Mount Pinatubo on the Philippines interrupted the trend of global warming for two or three years.
A glacial outburst flood occurs when a volcano covered by a glacier erupts, melts the ice and releases a tremendous flood wave.
A lahar is a gigantic mudflow caused by a volcanic outburst, consisting of mixture of erupted material, loose soil and water, that can be extremely dangerous, covering large areas with a height of some meters and a possible breadth of more than a hundred meters, running with a speed of up to 100 km/h.