Transcript Volcanoes
Volcanoes
Volcanology: The study of volcanoes Vulcanologists: scientists who study volcanoes
Anatomy of a Volcano
Central vent: where major eruption occurs Flank vent: secondary vent Magma chamber: where magma stays until pressure forces it up the vent Fumarole: flank vent that releases gas only
A. Magma and Lava
Volcanism: any
activity that includes the movement of magma towards or on the Earth's surface
Magma
Magma: liquid rock - volcanic rock found below the Earth's surface; solid rock can become magma when liquid (water) is added (subduction zones)
Lava
: magma that
erupts
onto the Earth's surface Magma can flow onto Earth's surface through an opening -
vent
- or crack -
fissure
A
volcano
is any structure formed on Earth's surface by the vent and volcanic material that builds up around it
B. Major Volcano Zones
1.
Subduction zones
– a. oceanic lithosphere melts as it plunges beneath the continental plate, water added to mantle material creates magma ex. Ring of Fire b. ocean trenches where oceanic subducts under oceanic creates volcanic islands arcs ex. Aleutian Islands, AK, Japan
2.
Mid-ocean ridges
magma flows up through rift zone, can form underwater volcanoes ex. Iceland - MOR above sea-level; contains many fissures
3.
Hot spots
- in the middle of a plate is a spot where magma flows upward; plate moves over the hot spot and form a volcano; volcano is carried away by plate and become extinct ex. Hawaiian Islands A new Hawaiian island forming underwater Loihi
C. Types of Lava
The violence of an eruption depends on : type of magma (minerals) temperature of the magma The amount of dissolved gases
Viscosity
viscosity resistance to flow More viscous flows slowly Less viscous flows quickly
Mafic Lava
Dark colored Contains magnesium and iron Makes up oceanic crust Is hot and thin, less viscous - flows quickly - gases escape easily - "quiet flow" ex. Hawaiian volcanoes
Pahoehoe
If mafic lava cools slowly: forms wrinkly crust -
pahoehoe -
Hawaiian for "ropy"
Aa
if it cools quickly: it forms rough, jagged chunks -
aa
Lava Tubes
If outer edges cool quickly and inner lava still flows: creates tunnel called
lava tubes
Pillow Lava
Lava flowing out of fissures on ocean floor: cools quickly & forms rounded
pillow lava
Is light colored
Felsic Lava
Contains silica Makes up continental crust Is cool and thick, more viscous - lots of trapped gases - explosive!
ex. continental volcanoes Mt. St. Helens
D. Pyroclastic material
These are rock fragments sent into the air from explosive felsic lava eruptions They are described by size
Volcanic Dust and Ash
Volcanic dust< 0.25 mm in diameter Volcanic ash > 0.25 - 2 mm These may travel far from the eruption!!
Lapilli, Bombs and Blocks
Lapilli "little stones“ 2 - 64 mm; they fall near the vent Volcanic bombs clumps of lava sent spinning thru the air Volcanic blocks large rocks blasted from fissure; can be house-size
Pyroclastic flow
The most deadly aspect to volcanic eruptions Combination of hot, toxic gases coming from vents, up to 1000 C, and 750 km/hr More dense than air, so rolls into villages killing victims quickly (e.g. Pompeii) Video: http://videos.howstuffworks.com/discovery/7153-volcanoes-pyroclastic-flow-video.htm
E. Volcano Types
how do volcanoes form? http://videos.howstuffworks.com/discovery/27683 assignment-discovery-formation-of-volcanoes-video.htm
1. Shield Volcanoes
Form: when hot, mafic lava builds up around the vent - form cones Have wide, broad bases and gently sloping sides, medium height ex. Hawaiian Islands
2. Cinder Cone Volcanoes
Very steep sloped sides, short (few hundred meters) Formed from layers of ash and other explosive pyroclastic materials ex. Sunset Crater, AZ
3. Composite Volcanoes, or Stratovoclanoes
Composite means a mix of unlike things, “strato-” means layer Formed from alternating layers of lava and ash ex. Mt. Fuji, Mount Hood, Mt. St. Helens
Crater
A pit at top of volcano, formed when material is blown out Usually widens due to weathering and erosion Often a smaller cone may form inside crater When filled with water = a crater lake - Crater Lake National Park, Oregon
Caldera
A large, basin shaped depression formed from a crater If magma chamber is empty, the crater collapses - forms caldera Also formed from huge eruptions ex. Krakatau
F. Predicting Volcanic Eruptions
Scientists use the following to predict EQs: 1. seismographs monitor for small EQs from growing pressure, that often precede eruptions 2. slight bulging of surface from magma pushing out 3. change in ground tilt
4. gases 5. history of previous eruptions Very few volcanoes have a lengthy history to study; constant monitoring is required
G. Extraterrestrial Volcanoes
Moon - was
once volcanically active - evidence of lava flows Craters - a result of bombardment by meteorites)
Mars - many volcanoes and volcanic features Olympic Mons - shield volcano - 28 km above surface, base = 600 km; probably stayed on lava source for millions years (no plate tectonics) Still active volcanoes on Mars?? Not sure, but it is seismically active
Io
Moon of Jupiter Many active volcanoes more eruptions; more material ejected than on Earth each month; probably sulfuric lava Spectacular eruptions umbrella-shaped plumes hundreds km high Vulcanism probably caused by friction
Importance of Volcanoes
all original rocks on Earth's crust were formed from cooled magma and/or lava water vapor from volcanoes early in Earth's history may have formed oceans gases from early eruptions formed the atmosphere volcanism adds new crust and reshapes planet each year
Supervolcanoes
What are they?
http://6.cn/watch/3812360.html
Several on youtube.com
ex: under Yellowstone National Park http://dsc.discovery.com/convergence/supervolcano/supervolcano.html
Tsunami and landslides
Alaska: http://geology.com/records/biggest-tsunami.shtml
Volcano driven: East coast US (when ?) http://www.history.com/videos/mega-disasters-east-coast-tsunami#mega-disasters-east-coast-tsunami 10 ways the Earth will end :