Upload
evangeline-mills
View
236
Download
0
Tags:
Embed Size (px)
Citation preview
Concepts Location of active volcanoes
Volcanism 3 categories Viscosity
5 types of extrusive volcanism Examples of each
3 types of lava flows
Dangers of volcanic eruptions
Volcanism Definition: the origin and movement of magma
Three categories Extrusive: magma is expelled onto surface Intrusive: magma solidifies in the shallow crust near the
surface. Can be exposed after weathering. Plutonic: magma solidifies deep inside the crust.
Viscosity: The ability for lava to flow. Reflective of the amount of silica present in the magma.
LOW silica = LOW viscosity = nonexplosive HIGH silica = HIGH viscosity = explosive
5 Types of Extrusive Volcanism1. Shield Volcano Central vent allows
magma from chamber to spill out, slowly building the volcano in layers.
Produces wide, gently sloping mountains
Best example: Hawai’ian volcanoes (right: Mauna Loa)
“Stratovolcano” Central vent allows
magma to come up from chamber below
Produces symmetrical, steep-sloped mountains
Most “explosive” type of volcano
Examples: Mt Fuji,Mt Shasta, Mt St Helens
5 Types of Extrusive Volcanism2. Composite Volcano
5 Types of Extrusive Volcanism3. Caldera Volcano Formed when the upper part of a
volcano collapses The magma chamber below is (partially or
completely) emptied after an eruption The emptied magma chamber can no
longer support the weight of the overlying rock
The overlying rock collapses into itself, forming a circular basin
Volcanic activity can continue if there is still magma in the chamber below
Example: Crater Lake, OR
5 Types of Extrusive Volcanism3. Caldera Volcano example: Crater Lake, OR
Crater Lake was formed after Mt Mazama (a stratovolcano) eruptedand collapsed back in on itself.
Smallest mountain formation of all volcanic landform types
Cone-shaped peaks build up from small, solid particles, ejected into air by small volcanic vent
Generally <1,500’ high Example: Wizard Island
5 Types of Extrusive Volcanism4. Cinder Cones
5 Types of Extrusive Volcanism5. Lava Dome “Plug Dome” High-silica lava exits from
a vent. Due to its high viscosity (doesn’t flow very fast or far), it builds up into a dome.
Effectively “plugs” the main vent. Can still emit ash, gases, and even lava.
Example: Lava Dome in Mt St Helen’s crater.
3 Types of Lava Flows
’A’a “Clinky” Blocky, choppy lava flows that does not flow well over land
Pahoehoe “Smooth, unbroken lava” Ropy surface
Pillow Lava Lava emerges from underwater volcanic vents Lava cools & crusts when it hits colder water When crust fractures, lava oozes out and creates billowing
pillows
Dangers of Volcanic Eruptions Burning Hot Lava Earthquakes, Landslides and Tsunamis
These are often related – an earthquake might jar some land loose, resulting in a landslide. The earthquake may set off the tsunami. Also, if the landslide falls into the ocean, can trigger a tsunami.
Mudslides (“Lahars”) Ash Fallout Pyroclastic Flow (“nuée ardente”)
Dangers of Volcanic EruptionsMudslide (Lahar) examples
Mt. Pinatubo, Philippines1991 eruption
Mt. St. Helens, WA1980 eruption