VOLCANOES. volcanism - any activity which includes movement of magma toward or onto the earth’s...

VOLCANOES

volcanism - any activity which includes movement of magma toward or onto the earth’s surface

lava – molten rock at or above the surface

magma – molten rock below the surface

vent - the opening in the crust through which magma flows onto the surfacevolcano - the structure formed around the vent by layers of volcanic materials

Volcanoes occur mostly in areas near convergent and divergent plate boundaries.

oceanic plate subducts beneath a continental plate

seawater combines with the melting rock and mantle

violently explosive volcanoes

along the edges of the continents

examples: Andes, Cascades

Convergent Plate Boundaries oceanic crust and continental crust

Oceanic plates subduct below other oceanic plates

Chain of volcanoes produced behind the trench called island arcs

Example: Aleutian Islands, Alaska

Convergent Plate Boundaries oceanic crust and oceanic crust

Called mid-ocean ridges or rifts

Oceanic crust spreads apart

Creates new seafloor

Lots of magma comes to the surface here Undersea volcanoes can also be

present

Most go unnoticed, as they occur deep on the ocean floor

Divergent Plate Boundaries oceanic crust and oceanic crust

Mid-Ocean Ridge ExampleIceland

Diverging plates pull apart continents

Rift valleys are formed

have characteristic fissures (cracks in the crust that lava flows through

Example: Great Rift Valley, Africa

Divergent Plate Boundariescontinental crust and continental crust

East African Rift Valleycontinental crust and continental crust

Volcano formed from rift valleyMt.Kilamanjaro,Tanzania,Africa

HOT SPOTSStationary (non-moving)

areas of volcanism within the interiors of lithospheric plates

Plate above the hot spot continues to drift slowly

Plate carries the volcano on the surface away from the hot spot A new volcano begins to form over the hot

spot

Activity in the 1st volcano slows, then ceases.

Hot Spot Volcano ExampleHawaiian Islands

TYPES OF LAVA

Two general types

Depends on the chemical composition of the rocks and minerals

TYPE 1. FELSIC/ANDESITIC LAVAless dense

more viscous or thick/sticky (moves slowly)

lighter in color because it contains more silica (quartz is made of silica)

makes up most of the continental crust

TYPE 2. MAFIC/BASALTIC LAVA

denser

more fluidic

dark-colored

rich in Mg and Fe

forms the oceanic crust

TYPES OF MAFIC/BASALTIC LAVA

aa (pronounced ahh-ahh)

sharp, jagged surfaces

TYPES OF MAFIC/BASALTIC LAVA

pahoehoe (pronounced puh-hoy-hoy)

wrinkled, rope-like surface

VIOLENCE OF ERUPTIONSBasaltic/mafic lava

Very hot

Thin and fluidic

Gasses escape easily

“Quiet” eruptions

VIOLENCE OF ERUPTIONSAndesitic/felsic lava

Cooler flows

Thick (viscous) and “sticky”

H2O & CO2 gasses get trapped inside

Explosive and violent eruptions

LAVA TUBE - A LARGE PIPE FORMED FROM SUCH RAPIDLY COOLING BASALTIC LAVA THAT A HARDENED SHELL FORMS AROUND THE STILL-MOVING MOLTEN ROCK INTERIOR

DANGERS OF LAVA TUBESLooks like normal

ground on top, but can collapse when tourists walk over them

Poisonous gases can escape when lava tubes collapse

SHIELD VOLCANOES- HUGE VOLCANOES MADE OF BASALTIC/MAFIC LAVA, WITH BROAD BASES AND GENTLY SLOPING SIDES - THE HAWAIIAN ISLANDS

CINDER CONES - SMALL, STEEP-SIDED VOLCANOES MADE OF CINDERS AND OTHER PYROCLASTIC MATERIALS; THERE IS LITTLE LAVA FLOW, AND THEY OFTEN OCCUR IN GROUPS

Pu`u ka Pele

Paracutin

STRATOVOLCANO OR COMPOSITE CONE - LARGE, SYMMETRICAL VOLCANO MADE OF ALTERNATING LAYERS OF VISCOUS ANDESITIC OR FELSIC LAVA AND PYROCLASTIC MATERIALS; THESE ARE VERY DANGEROUS VOLCANOES WITH VIOLENT ERUPTIONS  

CRATER - FUNNEL-SHAPED PIT AT THE TOP OF A VOLCANIC VENT, FORMED WHEN VOLCANIC MATERIALS ARE BLOWN OUT OF THE TOP OF THE VENT

CALDERA - LARGE, BOWL-SHAPED DEPRESSION WHICH MAY FORM AT THE SITE OF A VOLCANO AFTER THE MAGMA CHAMBER BELOW EMPTIES OF MAGMA

CRATER LAKE IS A CALDERA WHICH FILLED WITH WATER AFTER THE ERUPTION AND SUBSEQUENT COLLAPSE OF MT. MAZAMA.

PYROCLASTIC MATERIALS

When viscous magma reaches the vent it will expand and release the gasses trapped inside. At this time a violent eruption occurs and lava is broken into pieces of all sizes.

INDIVIDUAL ERUPTIVE FRAGMENTS ARE CALLED PYROCLASTS ("FIRE FRAGMENTS").

TEPHRA (GREEK, FOR ASH) IS A GENERIC TERM FOR ANY AIRBORNE PYROCLASTIC ACCUMULATION. .

Volcanic Dust – pyroclastic material smaller than 0.25mm in diameter

VOLCANIC ASH - PYROCLASTIC MATERIAL SMALLER THAN 2 MM IN DIAMETER

LAPILLI (“LITTLE STONES”) - PYROCLASTIC MATERIAL LESS THAN 64 MM IN DIAMETER

VOLCANIC BOMBS - LARGE BLOBS OF LAVA THROWN OUT OF THE VENT WHICH COOL INTO A SPHERICAL OR OVAL SHAPE

VOLCANIC BLOCKS - HUGE PIECES OF SOLID ROCK BLASTED FROM THE VENT 

FISSURES - CRACKS IN THE CRUST THROUGH WHICH LAVA FLOWS

PILLOW LAVA - UNDERSEA BASALTIC LAVA WHICH COOLS RAPIDLY INTO LARGE, ROUNDED BLOBS; ALSO KNOWN AS PILLOW BASALTS  

LAHARS ARE VOLCANIC MUDFLOWS WHICH OCCUR WHEN ASH AND DEBRIS BECOME SATURATED WITH WATER AND FLOW DOWN THE VOLCANO’S SLOPES, USUALLY FOLLOWING STREAM VALLEYS.

OTHERS ARE TRIGGERED WHEN HEAT FROM THE VOLCANO MELTS SNOW AND ICE. 

7:3 EXTRATERRESTRIAL VOLCANISM

INDICATIONS ARE THAT MANY OF THE PLANETS AND MOONS, INCLUDING OUR MOON, HAVE BEEN VOLCANICALLY ACTIVE IN THE PAST.  

THE NEAR SIDE OF THE MOON IS COVERED WITH BASALTIC LAVA FLOWS WHICH FILLED IMPACT CRATERS.THESE ARE CALLED MARIA, AND SUGGEST THAT VOLCANISM WAS ONCE PRESENT ON THE MOON.

SCIENTISTS HAVE NO EXPLANATION FOR LUNAR VOLCANISM, AS THERE IS NO EVIDENCE OF PLATE TECTONICS OR CONVECTION CURRENTS TO SUPPLY THE HEAT REQUIRED FOR SUCH ACTIVITY.

PERHAPS THE HEAT MAY HAVE COME FROM A LONG PERIOD OF INTENSE METEORITE BOMBARDMENT.  

IMAGES FROM SPACECRAFT HAVE SHOWN NUMEROUS VOLCANOES AND VOLCANIC FEATURES ON MARS.  

THE LARGEST OF THESE IS A HUGE SHIELD VOLCANO, OLYMPUS MONS, WITH ITS SUMMIT THREE TIMES HIGHER THAN MT. EVEREST AND ITS BASE THE SIZE OF ARIZONA. 

VIKING LANDING CRAFT HAVE DETECTED “MARSQUAKES”, SO THE PLANET MAY ALSO BE ACTIVE SEISMICALLY.

IO, A MOON OF JUPITER, IS THE MOST VOLCANICALLY ACTIVE BODY IN OUR SOLAR SYSTEM. 

BECAUSE IO IS SO BRILLIANTLY COLORED, SCIENTISTS THINK THAT THE VOLCANIC MATERIAL BEING EJECTED FROM NINE KNOWN VOLCANOES IN UMBRELLA-SHAPED PLUMES IS PRIMARILY SULFUR AND SULFUR OXIDES.

EVERY MONTH, ABOUT THE SAME AMOUNT OF VOLCANIC MATERIAL RELEASED FROM THE 1980 MT. ST. HELENS ERUPTION, SPEWS OUT AND COVERS IO’S SURFACE.

Olympus Mons:

A Shield Volcano

on Mars

Earth’s Largest Volcano: Mauna Loa9 km high

120 km across

Olympus Mons:24 km high

550 km across

x 3 =

Mars ≈ 1/2 of Earth’s diameterOlympus Mons ≈ 3 times the size of Earth’s largest VolcanoHuge size disparity due to Mars’ stationary crust, henceenormous hot-spots that build-up in stationary positions

IT IS THOUGHT THAT AS IO IS PULLED BACK AND FORTH IN ITS ORBIT AROUND JUPITER BY JUPITER’S OTHER MOONS, ITS SURFACE MOVES UP AND DOWN, BUILDING UP HEAT FROM FRICTION. 

THIS SURFACE MOVEMENT MAY RESULT IN THE MELTING OF THE INTERIOR AND VOLCANISM.