Effusive volcanoes are more commonly formed at constructive plate margins where plates diverge. Here, lava tends to be basaltic meaning it is low in silica content. The low proportion of silica allows gases to expand and thus
These types of lava are very viscous due to its high silica content. This is because the lava rises from the subduction zone through continental lithosphere which has a low density and is filled with air spaces containing gases which become incorporated into the lava. This very viscous lava often blocks off vents of volcanoes and when the pressure building up in the vent is eventually released, the top of the volcano can be blown off leaving a huge crater, such as in the 2002 eruption of Mount Etna in Sicily. When the two plates involved are oceanic, explosions tend to be less violent than this as the melted lithosphere which forms the lava is denser and so contains fewer gases. At constructive boundaries where plates are moving apart from one another, basaltic lava is erupted between the gaps.
Haiti is on the boundary of the Caribbean and North American plates and is an example of a conservative plate boundary. Volcanic eruptions are also one the greatest threats among the natural hazards. The active land, volcanoes of the world occupy are only 0.6% of the total land area. Most volcanoes are spread along the coast, in areas that are also earthquake zones. Mid-ocean volcanic ridges are formed where the ocean floors split and move apart.
8. How does hornfels form? Rock contacts with magma and bakes rock. 9. Know that the type of metamorphic rock relates to how much heat and pressure the rock was exposed to.
It allows us to understand how sedimentary rocks, metamorphic rocks, and Igneous Rocks use one another to not only form the Rock Cycle, but also other processes that are important to our planet. The rock cycle beings with hot magma, deep below the earth’s surface. Once the magma dries, crystallization occurs, and results in igneous rocks. Over time weathering occurs to the igneous rocks. Over time weathering takes over the igneous rocks.
Thicker, more viscous magma has a greater potential for explosive eruptions and therefore represent the greatest potential hazards. The thickest type of magma is known as Acid Magma. Its relatively low temperature (600C-1000C), high silica content and low proportion of dissolved gases causes its toothpaste-like consistency that leads to blockages and powerful eruptions. This can mean that the eruptions caused by thick magma can be less frequent and more difficult to predict, meaning that when an eruption does occur, it is usually with little or no warning, which can lead to catastrophic consequences as any nearby settlement will be relatively unprepared for the effects of a violent volcanic eruption. Furthermore, acid magma is more likely to produce clouds of smoke and ash due to the explosive nature of the eruption it causes, than thinner, basic lava.
Volcanoes are found mainly in three locations, at constructive and destructive plate margins and at hotspots. The most dangerous volcanoes occur at destructive, convergent plate margins. Here one plate subducts beneath the other, and as it descends, friction, increasing pressure, and heat from the asthenosphere and mantle melt the plate to form an acidic magma chamber. The magma at these boundaries is andesitic and rhyolitic, meaning that they have a high viscosity. Because of this the lava is resistant to flow and often forms blockages in vents.
Science is showing that the potential for an eruption of some of the earth’s biggest and deadliest volcanoes is very real and imminent. In order to understand why volcanoes are deadly, one must know what causes volcanoes to erupt. Deep down in the earth’s crust or mantle there is melting occurring. This heat is coming from the earth’s core and the constantly moving materials within the earth. When parts of the mantle or crust melt, magma is formed.
How do we know that the Earth has a liquid core? Why is the inner core solid even though it is hotter than the outer liquid core? We know that the Earth has a liquid core because of seismic waves. A type of seismic wave known as an "S" wave or Shear wave moves side-to-side in a shearing motion and does not propagate through liquid only through solid. "S" waves are often blocked or reflected by the inner core and it is therefore thought
When the eruption did occur it was seen as explosive as it produced large volumes of acidic lava, ash, pyroclastic flows and steam. However, volcanoes at constructive plate margins or hot spots are generally seen as less explosive. They produce continuous, yet gentle, eruptions of lava, such as the formation of the