Chapter 12 Volcanoes

Introduction  A volcano is the opening in the Earth that erupts gases, ash and lava.  There are over 1500 volcanoes in the world.  Over 600 are currently active.  169 volcanoes in the Unites States are currently active. Being monitored by the USGS  Kilauea in Hawaii is the most active (but not explosive) volcanoes on Earth  Check out chart on 346 – why not explosive?

Mauna Loa on Hawai'i Big Island (active) is world’s biggest volcano.

 Olympus Mons is a shield volcano that towers to an amazing 26 km. That makes it 3 times the height of Mt. Everest. Unlike Everest, Olympus Mons has a very gentle slope. It is up to 550 km at its base.

Active – Dormant - Extinct  Active – is a volcano that has had at least one eruption during the past 10,000 years. May be dormant or erupting.  Dormant – have note erupted recently, but may at any time  Extinct – have not erupted in over 10,000 years.

 Since 1980, 45 eruptions and 15 cases of notable volcanic unrest have occurred at U.S. volcanoes. t 3  Many volcanoes are found underwater.  Where are a good deal of these located?  In some cases, lava can build up high enough to form islands (Hawaii, Iceland)  Test question - tell what creates the volcanoes at each of the locations on the following slide.

Types of magma  Basaltic  42-52% silica content  Dark in color  Low viscosity  Non-Explosive  Low gas content  Andesitic  52-66% silica content  Granitic:  >66% silica content  Lighter in color  High viscosity  High gas content  Explosive

Viscosity  A liquid’s ability to resist flow  Related to SiO 2 - More silica = more viscosity  Low viscosity – runny - watery  High viscosity – thick - milkshake

Magma composition  Page 350  Be able to classify the three types of magma based on their silica content.  Volcano Apps WK – quiz next week  Thursday or Friday

Types of volcanoes  Shield: gentle-sloped, quiet eruptions, basaltic lava, low sillica- content, low trapped-gas content. Kilauea.  Composite: made of both lava and tephra. Mount Rainier.  Cinder cone: steep-sloped, made of tephra, explosive, granitic lava, high silica, high trapped gases. Krakatoa.

Hazards from volcanoes  Lava (enough said)  Volcanic ash - can cause lung cancer, can also smother crops and cause other damage  Pyroclastic flows  Lahars  Poisonous gases - sulfuric gases (rotten eggs). Can also combine with water vapor to create sulfuric acid and cause acid rain  Can cause tsunamis

Pyroclastic Flows  Flow of extremely hot material including ash, poisonous gas and tephra.  Can reach 700 km/h (450 mph). [2] The gas can reach temperatures of about 1,000 °C (1,830 °F). [2]  #1 cause of volcano-related deaths  (29,000 at Mount Pelee 1902)

Lahars  A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water  Vary in size, speed and deadliness.  Snow and glaciers can be melted by lava or pyroclastic flows during an eruption. Snowglaciers pyroclastic flows  The 1991 eruption of Mount Pinatubo caused lahar flows: the first eruption itself killed six people, but the lahar flows killed more than 1500.eruptionMount Pinatubo

Predicting volcanic eruptions  There can be several signs that sometimes help predict the eruption of an earthquake and necessitate evacuation:  Seismic activity  Bulging of volcano’s exterior  Gas Emissions  Thermal monitoring  Mass movements

Plus Sides to volcanoes  New Land  Fertile Soil  Geothermal Energy  Mineral Resources  aluminum, diamonds, gold, nickel, lead, zinc, and copper.  Tourism  Spas and resorts

 Volcano: an opening in the Earth where lava, ash and gas escapes

 Tephra: rock thrown into the air  ephra_sizes.jpg ephra_sizes.jpg  nce.gif

 Shield: gentle-sloping volcano, generally display quiet eruptions

Crater - a circular depression in the ground caused by volcanic activity

 Vent: opening of a volcano

 Dike: a vertical igneous rock formation.

 Magma: hot, melted rock beneath the surface.

 Caldera: large crater formed when a volcano collapses

 Cindercone- steep sided volcano known for explosive eruptions

 Neck: a solid igneous core that remains after the volcano has been eroded.

 Batholith: intrusive igneous rock formed under ground

 Composite- volcano made of both lava and tephra

 Sill- horizontal igneous rock formation

 Pluton - any type of igneous rock intrusion

 Hot spot- place above an exceptionally hot part of the mantle. (not at plate boundaries)

Tephra  First, what type(s) of volcano erupts tephra as a product?  Classified by size  Ash - particles smaller than 2 mm (0.08 inches) in diameter Ash  Lapilli or volcanic cinders - between 2 and 64 mm (0.08 and 2.5 inches) in diameter Lapilli  Volcanic bombs or volcanic blocks - larger than 64 mm (2.5 inches) in diameter. Volcanic bombsvolcanic blocks

Where do volcanoes occur?  See map, page 337  Divergent boundaries  Subduction zones  Hot spots  Know two realistic examples of each