Most of the sixty-plus volcanoes that erupt each year are low risk, however a combination of factors can cause a volcano to be a serious hazard. The factors causing these variations will be explained in this essay. The first factor that must be considered is the viscosity of the magma. This can determine how powerful an eruption is and what shape the volcano eventually becomes. Viscosity can be affected by three main factors, Firstly, the higher the temperature, the lower the density of the magma, causing it to flow more easily.
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.
It is the viscosity of magma that largely determines the nature and power of an eruption and the resultant severity of the hazard. Basic magma has a high proportion of dissolved gases and low silica content, making it very fluid. On the other hand, acidic magma is very rich in silica and has a relatively lower temperature, making it very thick and slow moving. The more viscous the magma, the greater the potential for explosive eruptions and these represent the greatest potential hazards. Non-explosive eruptions tend to produce mostly lava flows, which do not represent a particularly serious hazard to people, however they will destroy farmland and buildings.
Due to high temperatures in the mantle of around 3000 degrees centigrade, this oceanic crusts melts and then rises due to the convection currents in the aesthenosphere . As it joins with trapped seawater and sediment, it melts the overlying continental crust, and the magma plumes rise to the surface. They contain more silica so are more viscous, which plugs up the volcano, meaning pressure build up. This is why these volcanoes are so explosive. Another type of plate boundary are constructive, which is the margin between two diverging plates where new magma
em study guide99 Chapter 8 Unit Conversions Review Skills 8.1 Unit Analysis An Overview of the General Procedure Metric-Metric Unit Conversions English-Metric Unit Conversions 8.2 Rounding Off and Significant Figures Measurements, Calculations, and Uncertainty Rounding Off Answers Derived from Multiplication and Division Rounding Off Answers Derived from Addition and Subtraction 8.3 Density and Density Calculations Using Density as a Conversion Factor Determination of Mass Density 8.4 Percentage and Percentage Calculations 8.5 A Summary of the Unit Analysis Process 8.6 Temperature Conversions Chapter Glossary Internet: Glossary Quiz Chapter Objectives Review Questions Key Ideas Chapter Problems Section Goals and
What is the percent of CO2 in the atmosphere that humans are emitting per year relative to preanthropogenic levels? (Hint: divide the rate of increase (2 ppm/year) by the amount of CO2 in 1850. and multiply by 100). 5. There were 600 gigatons (106 tons) of carbon in the atmosphere in 1850. How many gigatons accumulated in the atmosphere each year due to human activity?
D. Scholar Geography 1 November 11, 2012 Test Corrections #1 Question: Which atmospheric heating process involves the emission of energy from an object? Correct Answer: E) Radiation My Answer: D) Why it’s Wrong: Radiation is the right answer because it has much stronger. It’s stronger than transmission, scattering, reflection and absorption. A good example would be: if your wearing a black shirt out in the sun you would be much hotter than if you’re wearing a white shirt. The black shirt would also fade over time because the suns rays would eat up the shirt.
While one might ask how water erosion can be so prevalent in the desert, it is important to note that like many Australian deserts, the area receives a surprisingly high amount of rain, about 200-250 millimeters a year. ("Ayers Rock Facts," 2009) It is believed that the mountain chains that once included Ayers Rock were as large as the surrounding peaks. Now, there is just one remaining piece of this long lost chain. Wind and water took an enormous toll on the surface of the area. When one considers other major mountain chains, and is informed that they were once much larger, it is hard to grasp the concept due to the fact that the mountains still exist, and are fairly large in their current state.
bfly_recent.gifFrom the research, sunspots do not appear at random over the surface of the sun but are concentrated in two latitude bands on either side of the equator. The sunspots are greatly related to our climate. While the solar cycle has been nearly regular during the last 300 years, there was a period of 70 years during the 17th and 18th centuries when very few sunspots were seen (even though telescopes were widely used). This drop in sunspot number coincided with the timing of the little ice age in Europe, implying a Sun- to-climate connection. limb_flare_sm.jpg (5710 bytes)Solar flares are tremendous explosions on the surface of the Sun.
Heat Exhaustion Signs and Symptoms The signs and symptoms of heat exhaustion include but are not limited to confusion, dark-colored urine, excessive thirst, dizziness, fainting, fatigue, headache, muscle cramps, nausea, pale skin, profuse sweating, and rapid heartbeat. Risk Factors Heat index has a major affect on the chance of experiencing heat exhaustion. Your risk increases when the heat index is ninety degrees or more. Your body’s ability to cool itself decreases significantly in sixty percent relative humidity or higher. Another risk factor is the “heat island effect”.