volcanoes

• Active volcanoes are those that have a record of eruption within the last 600 years or those that erupted 10,00 years ago based on analyses of their materials
• INactive volcanoes are those that not gave erupted for the last 10,000 years and their physical form is being changed by agents of weathering and erosion though formation of deep and long gullies
• according to philvolcs our country has more than a hundred volacanoes as of 2013
• Twenty three are active
• a crater is a funnel-shaped opening at the top of a volacano
• A caldera is formed when a part of the wall collapses following an explosive eruption
• There are primary factors affecting the volcanoes eruptive style namely:

  1. the magma's temperature
  2. its chemical composition
  3. the amount of dissolved gases it contains
• the viscosity of magma decreases with temperature
• the higher the temperature of magma is, the lower its viscosity
• magmas with high silica content are more viscous than those with low silica content
• Lava with less silica content has low viscosity that it can travel a great distance, forming a thin sheet
• kava with high silica content is too viscous to travel far and tents to break up as it flows
• lava with low amount of gas and high silica is very viscous and does not flow out at all as it rises, forming a columnar plug in the vent
• lava with low amount of gas as it rises has high viscosity that it piles up at a vent resulting in a dome
• Types of volcanic eruptions:

  1. phreatic or hydrothermal
  2. phreatomagmatic
  3. strombolian
  4. vulcanian
• Phreatic or hydrothermal is a stream driven eruption as the hot rocks come in contact with water
• Phreatomagmatic is a violent eruption due to the contact between water and magma
• Strombolian is a periodic weak to violent eruption characterized by fountain lava
• Vulcanian are characterized by tall erupton columns that reach to 20km high with pyroclastic flow and ashfall tephra
• three volcanic cones

  1. shield
  2. cinder
  3. composite cones
• shield volcanoes are formed by the accumulation of lava that oozes out from the volcano
• cinder cones are built from ejected lava fragments
• composite cones or stratovolcanoes are large nearly perfect sloped structure formed from alternate solidification of both laba and pyroclastic deposits
• The Philippines ranks second in the world's production of geothermal energy
• according to department of energy 14.4 of the country's total power generation is produced from the geothermal energy
• The heat from the earth's interior is a source of energy called geothermal energy
• geothermal energy is generated in two ways: geothermal power plants and geothermal heat pops
• PRIMARY FACTORS AFFECTING THE VOLCANOES ERUPTIVE STYLE: THE MAGMAS THEMPERATURE, CHEMICAL COMPOSITION AND AMOUNT OF DISSOLVED GASES
• magmas with high silica content have higher viscosities than those with low silica contents
• The higher the temperature of magma, the lower its viscosity
• Magmas with high silica content are more viscous than those with low silica content
• lava with less silica content has low viscosity that it can travel a great distance, forming a thin sheet
• lava with high silica content is too viscous to travel far and tends to break as it flows
• lava with low amount of gas and high silica content is very viscous and does not flow at all as it rises forming a columnar plug in the vent
• lava with low amount of gas as it rises has high viscosity that it piles up at a vent resulting into a dome