Lava cover
Lava ceilings are layers of rock made of solidified lava . They range in size from individual to a few meters thick lava sheets and lava flows of a single volcano to the flood basalts of the magmatic large regions occurring in country-sized deposits , which are built up from kilometer-thick stacks of individual lava sheets. They form common landforms in tectonically or volcanically active regions of the earth, and appear to play a major role on other planets and moons of the solar system .
Emergence
Lava blankets are created by the leakage of lava from volcanoes such as shield volcanoes and volcanic crevices . Volcanic ceilings can also be created by ignimbrite , as this special form of lava spread also forms extensive ceilings. The large-scale lava covers that occur on earth are mainly effluent rocks such as basalt and rhyolite . The subsurface of lava ceilings can consist of sedimentary or volcanic rocks, in some cases the lava lies directly on the basement of the shield regions of old cratons . In many cases, volcanic tunnels and swarms of tunnels have been preserved along with the lava ceilings and in their interior , which can be the ascent paths of the lava.
The expansion of volcanic blankets depends largely on the properties of the invading lava. The amount and duration of the outflow is determined by the magma replenishment. Thin- flowing basalt lava, such as B. reaches the surface of the earth in extensive shield volcanoes , can flood areas of 100 km² and more and are thus the cause of various very extensive tabular countries .
Landform
Large-scale outflows of igneous rocks form typical landscape forms, such as plateaus and large strata . They can shape wide landscapes in the form of table lands or flat summit corridors, or only occur locally as table mountains or isolated witness mountains . The step-like gradation of the land surface of some of these landscapes gave rise to the coining of the term Trapp .
The cause of the landform development is the rock formation - mostly uniform mineralogical composition and a fine-grained nature of the base mass - in combination with the formation of extensive fissures , which leads to the formation of smooth fracture walls or rock dividing surfaces. Due to its formation, the rock is stable and resistant to weathering . For these reasons, lava covers form steep steps at the edges and valleys, while inside the terrain surface is flat or has only slight inclines.
The occurrence of fracture tectonics with the formation of clumps and trenches as well as the erosion of a large-scale lava cover over longer geological periods can cause a relief reversal .
Occurrence
Clear traces of lava cover can be seen in the Maria des Mondes or on the Martian volcanoes .
Examples of land-forming lava blankets on earth can be found in the rhyolite-ignimbrite blankets of the Puna in Argentina , in the Paraná basin of the Brazilian table or in the Camperdown District of Victoria . The Siberian Trapp in the Central Siberian Mountains or the Dekkan Trapp in India , like the Columbia plateau basalt in the north-western USA, consist of many layers of lava on top of each other. Landscape-shaping lava layers occur in Europe, for example, on the Hoher Meissner , in the Rhön and on the Vogelsberg , furthermore on the Teichelberg in the southern Fichtelgebirge and in the Eastern Styrian hill country .
literature
- Frank Ahnert: Introduction to Geomorphology . 1st edition. Verlag Eugen Ulmer, Stuttgart 1996, ISBN 3-8252-8103-5 , p. 55, 63 ff .
- Werner Zeil: Brinkmann's outline of geology, first volume: General geology . 12th edition. Ferdinand Enke Verlag, Stuttgart 1980, ISBN 3-432-80592-6 , p. 164 ff .
Individual evidence
- ↑ Volcanic landforms in the Camperdown area of Victoria. (No longer available online.) University of Sydney, archived from the original on February 8, 2012 ; Retrieved June 20, 2010 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
