Volcanos

• Volcanos interact with the atmosphere, through the release of green house gases
• Sulfur Dioxide emitted from volcanos can reflect shortwave radiation from the sun back out into space, cooling the temperature of earth
• volcanos provide nutrient rich soils, new crust, precious gems and most metal deposits. They are also responsible for the formation of the atmosphere and ocean
• Extreme and early life formed around volcanic vents where they used chemosynthesis to extract energy from chemicals and minerals flowing from hydrothermal vents
• Volcanism, is where solids, liquids, gases, and their mixtures erupt to the surface of a body.
• decompression melting occurs at diverging boundaries where hot rock rises, resulting in a decrease in pressure and the melting of rock
• there are three ways in which rock melts in the mantle: decompression, fluid-inducing and temperature variation
• 80% of volcanoes on Earth occur at convergent boundaries, 15% at divergent boundaries, occasionally at hot spots and very rarely at transform faults.
• Melt is molten rock found within the mantle, magma is found within the crust and lava on the surface
• Magma accumulates in the crust at magma chambers
• types of volcanic eruptions include: vertical (fissures, dykes), horizontal (sills) and central vents
• residence time is the time taken of melt to reach the surface, the length of time effects the lava's final composition
• Melt that has a fast transit time doesn't cool and avoids modification, solids in the melt remain and assimilation (melting of local crust) does not have time to occur
• Diatremes are caused by fast moving gas charged magma that result in explosive eruptions
• Melt with slow transit time cools as it reaches the surface resulting in the precipitation of minerals and the exsolution of gases, while also heating the surrounding rock resulting in a change in composition, solids are left behind due to gravity and only 10-30% of magma is erupted as lava
• Magma may slow many times resulting in multiple magma chambers beneath volcanos
• Lava contains solid, liquid and gas and its type is determined by its composition and viscosity (effected by its composition)
• the composition of lave ranges from relatively unmodified (low in silica and high in iron and magnesium), modified and highly modified (high silica). Unmodified lava is dark in colour (basalt) with the rock getting lighter as modification occurs
• the viscosity of lava is largely dependent on temperature and composition. The more silica present the more viscous the lava.
• Lahars are volcanic mudflows caused by the mix of water and volcanic debris, they can be hot or cold and no eruption is needed to cause them
• Pyroclastic flows (ash and rock) are extremely hot and fast, caused by expanding gas escaping from the viscous magma, as the magma rises and pressure decreases
• magma is liquid and less dense than the rocks that produce it, floating upward through the lithosphere as it accumulates
• Magma may find a way to the surface by fracturing the lithosphere along zones of weakness
• Magma may find a way to the surface by melting the the lithosphere above it
• Most magma refreezes before reaching the surface
• the processes needed to describe the sequence of events from melting to an eruption constitute a volcanic geosystem
• Shield volcanoes are produced by central eruptions of basaltic lava which flows easily and spreads widely
• Volcanic domes are generally produced by rhyolitic or andesitic lava flows as their more viscous nature produces steep-sided domes
• Cinder cones are created from volcanic vents that erupt pyroclasts (solid fragments), large fragments remain close to the vent while finer particles are carried further, resulting in a concave-shaped cone
• craters occur at the summit of most volcanos, surrounding the central vent
• Calderas occur when a large magma chamber empties and can no longer support its roof, resulting the the overlying volcanic structure collapsing leaving a basin-shaped depression much larger than a crater
• diatremes occur when the vent and feeder channel of a volcano are left filled with volcanic breccia after an eruption. Sedimentary rock around the diatreme may be weathered away leaving a diatreme jutting out of the ground
• Volcanoes eruption style is dependent on: magma/lava viscosity, the dissolved gas content of the magma, temperature, and environment (ocean/land)
• Two types of eruption styles are effusive and explosive
• VEI is a volcanoes explosively index (1-8 scale)
• the form/structure of a volcano is dependent on: the type of lava, rate of melt, environment, plumbing system and material ejected during an eruption
• fluid-inducing melting occurs at subduction zones where water is sub-ducted into the mantle with the sinking crust, lowering the melting point of the rock
• temperature variation in the mantle can cause mantle plumes which melt the lithosphere (crust) at hot spots
• the movement of the tectonic plate over a hot spot in the mantle helps indicate past plate movement
• fissures are constructive non-central volcanic eruptions, found along mid-ocean ridges, they produce large volumes of lava and form new ocean crust.