Volcanoes

• Volcano - a natural opening in the surface of the earth where molten rocks, hot gases, smoke, and ash are ejected.
• A volcano is a cone-shaped
• Summit - highest point of a volcano (peak).
• Crater - a funnel-shaped opening at the top of a volcano. They are formed by the outward explosion of rocks and other materials from a volcano.
• Mt. Mayon is one of the example that has a one crater.
• Caldera - formed when a part of the wall collapses following an explosive eruption. They are formed by the inward collapse of a volcano.
• Mt. Pinatubo is the best example for a caldera.
• Slope - sides or flanks of a volcano that create its shape and landforms.
• Base - the bottom part of the volcano which is considered as its support and foundation.
• Dust, ash, and rock - fragments of rocks; fine-grained lava.
• Vent - an opening in the surface of a volcano that emits lava, gases, ash, or other volcanic materials.
• Lava - molten rocks that has been extruded during an eruption.
• Magma - molten rocks that are still under the ground.
• PHIVOLCS (Philippine Institue of Volcanology and Seismology) - is a service institute of the Department of science and technology (DOST) that is principally mandated to mitigate disasters that may arise form volcanic eruptions, earthquakes, tsunami, and other related geotectonic phenomena.
• Active volcanoes - have record of eruption within 600-10,000 years ago. They are 24 active volcanoes in the Philippines.
• Inactive volcanoes - not erupted for the past 10,000 years.
• Potentially Active Volcanoes - are morphologically young -looking but with no historical records of eruption.
• Shield volcanoes - formed by accumulation of lava that resembles a warrior's shield. Eruptions are less explosive. Lava that comes out is less sticky. Because the lava is runnier, it travels farther from the crater before it cools, causing the shield-like shape of volcano as many eruptions build over-time.
• The example for shield volcano is Mt. Mauna Loa in Hawaii.
• Cinder cone volcanoes - they have narrow base and steep slope, a wide crater, they are most abundant.
• Paricutin Volcano in Mexico is the example of a cinder cone volcanoes.
• Composite volcanoes - they are also called stratovolcano. They are large, symmetrical and almost perfect slope. Their lava is stickier, and their eruptions are dangerous.
• The best example for a composite volcano is Mt. Mayon in Albay, Bicol.
• Lava flows - are the effusive (non-explosive) outpourings of lava, and usually flow slower than walking pace.
• Lava fountains - are a fountain of runny lava fragments from a vent or line of vents (a fissure). They can form spatter piles, and if the fragments accumulate fast enough, they can form lava flows.
• Lava domes - are mounds that form when viscous lava is erupted slowly and piles up over the vent, rather than moving away as a lava flow. They are generally caused by viscous, thick, sticky lava that has lost most of its gas. They can range in volume from a few cubic meters to cubic kilometers.
• Volcanic ash or ash clouds - are expelled in the atmosphere and is composed of pulverized rocks and glass created during eruption.
• Volcanic bombs - are the chunks of lava blasted into the air which solidify before reaching the ground. Their sizes may vary and can measure up to 64mm in diameter.
• Pyroclastic glow - are fast moving current of hot gases and rock travelling downhill form a volcano. The gases can reach tenperature of more than 1,000⁰C and can move up to a speed of 700 km/hr.
• Tephra fall - refers to the fragmented material that consist of pumice, scoria lithic materials or crystals, or combination of the four.
• Lahar or mudflow - are flowing mixtures or volcanic debris and water. They are classified as primary hot which directly associated with volcanic eruption or as cold lahar when they are caused by heavy rainfall.
• Volcanic eruption - occurs when magma and other volcanic materials are released to earth's surface.
• Types of volcanic eruptions: .

  • Phreatic
  • Phreatomagmatic
  • Vulcanian
  • Strombolian
  • Plinian
• Phreatic or Hydrothermal - is a stream-driven eruption when rising magma makes contact with ground or surface water.
• Phreatomagmatic - a violent eruption due to the contact between external water and magma.
• Strombolian - eruption driven by the bursting of gas bubbles with magma. A periodic weak to violent eruption characterized by fountain lava.
• Vulcanian - are small to moderate explosive eruptions, lasting for second to minutes. Talk eruptions columns (ash columns) that reach up yo 20km high with pyroclastic flow and ash fall tephra, lava blocks, and bombs.
• Plinian - eruptions that start suddenly and unexpedtedly after a long period of dormacy. Excessively explosive type of eruption of gas and pyroclastics.
• Factors affecting volcanic eruptions:

  • Viscosity
  • Temperature of magma
  • Composition of magma
  • Amount of gas
• Viscosity - is the property of the material's resistance to flow. It is also described as the liquid's thickness and stickiness.