Transcript Volcano ppt notes

VOLCANOES
 Chapter 9 Section 3, pp. 260 - 265
 Standard: The relationship between movement of the tectonic plates
and major geologic events, such earthquakes and volcanoes
EQ: WHAT IS A VOLCANO?
 Volcano is a vent of fissure in the Earth’s surface through
which magma and gases are expelled.
 Magma is molten rock forced to the Earth’s surface
 Lava is magma that flows onto the Earth’s surface
EQ: WHAT ARE 2 TYPES OF
VOLCANIC ERUPTIONS?
Non-Explosive:
 The most common type of eruption
 Produces relatively calm flows of lava
 Found in much of the seafloor, Northwest regions of the US,
& other vast regions on Earth’s surface
 Examples: Mauna Loa & Kilauea in Hawaii
EQ: WHAT ARE 2 TYPES OF
VOLCANIC ERUPTIONS CONTINUED:
Explosive:
 They are rare, but very destructive
 Clouds of hot debris, ash, and gas repeatedly shoot out of the
volcano
 Pyroclastic flows erupt from the volcano producing molten rock,
which hardens in the air, and dust sized particles of ash. The ash
can reach the upper atmosphere and circle the Earth for years.
 The lava and large pieces of debris are blasted out of the volcano
in a matter of seconds. This can demolish an entire mountainside
in seconds.
 Example: Mount St. Helens in Washington state
SHIELD VOLCANOES
 Built of layers of lava released from non-explosive eruptions.
 Lava is very runny
 Layers of lava create a volcano with sloping sides
 Not very steep sides, but can grow to be enormous
 Tallest Mountain on Earth: Mauna Kea in Hawaii
MAUNA LOA (IN HAWAII)
CINDER CONE VOLCANOES
 Made of pyroclastic material from moderate eruptions
 Steep sides
 Small volcanoes
 Erupt for short periods of time
 Often occur in clusters on sides of volcanoes
 Erode away quickly because pyroclastic material is not
cemented together
 Paricutin ~Mexican volcano appeared in a cornfield in 1943
and erupted for 9 years
CERRO NEGRO (IN NICARAGUA)
COMPOSITE VOLCANOES
 AKA: Stratovolcanoes
 One of the most common types of volcanoes
 Form from explosive eruptions of pyroclastic material
followed by quieter lava flows
 Lava and pyroclastic material form alternating layers
 Broad bases and steeper towards the top
 EX: Mt. Hood, Mt. Shasta, Mt. Ranier, and Mt. St. Helens (all in
US); Mt. Fuji is in Japan
MOUNT ST. HELENS (WASHINGTON
STATE)
EQ: HOW DOES MAGMA FORM AND
MOVE?
 Forms in the lower crust &
 Formation of Magma
upper mantle
 Caused by changes in heat &
pressure
 Usually the result of
decreased pressure
 Rises to the surface since
magma is less dense than
rock
 Usually, at plate boundaries
Ex: Ring of Fire In Pacific
Ocean
EQ: WHERE DO VOLCANOES FORM?
 @Rift Zones
 Deep cracks between
divergent plates, like the
Mid-Ocean Ridge in the
Pacific & North Atlantic
Oceans
 Remember Seafloor
Spreading
 @Convergent
Boundaries/Subduction
Zones
 At oceanic & continental
plates
 Oceanic crust subducts
under continental crust
 Oceanic water mixes with
the mantle rock, melts it &
allows magma to rise
 @Hot Spots
 Volcanically active areas
far from plate boundaries
 Example: Hawaiian Islands
EQ: HOW DOES A SCIENTIST PREDICT A
VOLCANO IS GOING TO ERUPT?
Classified in 3 categories
 Extinct: has not erupted in recorded history and probably
will never erupt again
 Dormant: currently is not erupting, but the record of past
eruptions suggests the volcano will erupt again
 Active: currently erupting or shows signs of erupting again
in the near future
SUMMARY
 Explain how an earthquake can set off a volcano?