Science 3rd QE

• Volcanoes are powerful natural forces resulting from a massive rupture in the Earth’s crust, spewing hot lava, volcanic ash, and toxic fumes onto the surface and air
• Volcanoes leave a lasting mark on the landscape
• Specific parts of a volcano:

  • Magma: Molten rock beneath Earth's surface
  • Parasitic Cone: A small cone-shaped volcano formed by an accumulation of volcanic debris
  • Sill: A flat piece of rock formed when magma hardens in a crack in a volcano
  • Vent: An opening in Earth's surface through which volcanic materials escape
  • Flank: The side of a volcano
  • Lava: Molten rock that erupts from a volcano and solidifies as it cools
  • Crater: Mouth of a volcano that surrounds a volcanic vent
  • Conduit: An underground passage magma travels through
  • Summit: Highest point; apex
  • Throat: Entrance of a volcano; the part of the conduit that ejects lava and volcanic ash
  • Ash: Fragments of lava or rock smaller than 2 mm in size that are blasted into the air by volcanic explosions
  • Ash Cloud: A cloud of ash formed by volcanic explosions
• Factors determining the type of volcano formed when magma erupts at the surface:

  • Viscosity, or stickiness, of the magma
  • Amount of gas in the magma
  • Composition of the magma
  • The way in which the magma reached the surface
• Two broad types of volcanoes are stratovolcanoes and shield volcanoes
• Stratovolcanoes have steep-sided slopes of about 30–35° due to highly viscous magma that doesn't flow far from the vent, building up in layers
• Other volcanic features that can form from erupted magma include cinder cones, lava domes, and calderas
• Shield volcanoes are formed when a volcano produces low viscosity, runny lava that spreads far from the source, forming a volcano with gentle slopes
• Examples of shield volcanoes include Mauna Kea and Mauna Loa
• Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes
• They are formed from viscous, sticky lava that does not flow easily, causing the lava to build up around the vent forming a volcano with steep sides
• Stratovolcanoes are more likely to produce explosive eruptions due to gas building up in the viscous magma
• Andesite, named after the Andes Mountains, is perhaps the most common rock type of stratovolcanoes
• Stratovolcanoes also erupt a wide range of different rocks in different tectonic settings
• Calderas are formed when a very large, explosive eruption empties the magma chamber beneath a volcano, causing the roof of the chamber to collapse and form a depression or bowl with steep walls on the surface
• Calderas can be tens of miles across and can also be formed during an eruption that removes the summit of a single stratovolcano
• The three stages of a volcano are:

  • Active
  • Dormant
  • Extinct
• Active volcanoes are classified as such if they are expected to erupt or are already erupting
• Dormant volcanoes are classified as volcanoes that are not erupting or predicted to erupt in the near future
• An extinct volcano is a volcano that no one expects will ever have another eruption
• Most volcanoes provide warnings before an eruption
• Magmatic eruptions involve the rise of magma toward the surface, generating detectable earthquakes, deforming the ground surface, causing anomalous heat flow, and changes in the temperature and chemistry of groundwater and spring waters
• Steam-blast eruptions can occur with little or no warning as superheated water flashes to steam
• Orbiting satellites monitor volcanoes from space, providing vital information and signs of a possible eruption
• Satellites use cameras to provide images and photos of volcanoes
• Satellites also provide information from special sensors that can detect:

  • Heat
  • Sulfur dioxide
  • Tiny changes in the shape of the Earth's surface
• All of this information can offer clues as to whether an eruption is imminent
• Seismographs measure movement in the planet's crust
• Volcanic eruptions are closely related to seismic activities that also cause earthquakes and tremors
• Seismographs are often used to monitor volcanoes because of their connection to seismic activities
• Tectonic plates scraping, sliding against each other, or moving apart cause vibrations and tension
• A violent seismic reading near a volcano is often a precursor to an eruption
• Tiltmeters, similar to spirit levels, are positioned on and around a volcano to monitor ground movement
• A small container of liquid in tiltmeters shows how much the ground moves, connected to computers that monitor ongoing changes in the landscape
• Changes in the landscape and deformations at ground level are often predictors of volcanic activity, as magma movements beneath the ground can cause visible bulging and hollows to form
• Hydrology is the study of water flows and groundwater
• Hydrologists use pressure sensors, water detectors, maps, and the naked eye to gather data
• Measuring hydrology on volcanoes serves two purposes
• Volcanoes emit gases, so measuring gas emissions around volcanoes can provide useful information about changes in behavior that could indicate an eruption
• Benefits of volcanic eruptions over geologic time:

  • Volcanic materials break down and weather to form fertile soils, cultivating which has produced abundant food and fostered civilizations
  • The internal heat from young volcanic systems has been used to produce geothermal energy
  • Metallic minerals like copper, gold, silver, lead, and zinc are associated with magmas found deep within the roots of extinct volcanoes