Lecture 29 Volcanoes. Sedimentation Types of volcanoes and lavas The Rock Cycle Chapter  14.17

Sedimentation Materials transported by the erosion agents are eventually deposited to form sediments. The ultimate destination of the debris is ocean. The material is carried toward the ocean in stages. It can be stored on the river banks (alluvial fans, river delta) or at places of old glaciers (moraine).fans deltamoraine Groundwater can deposit materials in the pore spaces of sediments, which are eventually converted to rocks. Dissolved materials precipitate in cracks to form veins. StalactitesStalactites and stalagmites are examples of groundwater depositions.stalagmites

Volcanoes A volcano is an opening in the earth’s crust through molten rock gets to the surface.opening The eruption material is called magma inside and lava outside.eruption There are 2 types of volcanoes: strato and shield.stratoshield Character of an eruption is determined by the viscosity of the magma and the amount of gas it contains. The more viscous the lava, the slower it moves. Volcanic gases include water vapor, CO 2, N 2, H 2, and sulfur compounds (temperature of ~1000 C). Currently there are ~1500 active volcanoes.active Nearly 50 erupt every year.

Lava Lava solidifies into various volcanic rocks. Types of lava: pahoehoe and a’a.pahoehoea’a The most common of these rocks, basalt, has a low viscosity.rocks More viscous andesite produces steep, conical mountains.viscous Rhyolite, the most siliceous one, produces small, thick flows and domes. Viscous and gaseous lava may solidify in pumice than contains many cavities and can float in water.cavities Molten rock that solidifies inside crust not reaching the surface forms intrusive bodies (plutons). They have larger grains than volcanic rocks on the surface, because of slower cooling (example, granite).

Summary There are only 3 different types of rocks according to their origin: igneous, sedimentary, and metamorphic. Rocks undergo a transformation cycle between these types.transformationcycletypes The Earth is still heated by radioactive elements which exist in its core since the formation time. The internal heating is responsible for Earth’s geological activity, including earthquakes. Erosion is an important process changing rocks on Earth due to the presence of the atmosphere.