INTRODUCTION: HOW DO VOLCANOES ERUPT?

1.) Heated material from deep (asthenosphere/mantle)rises as solid

2.) magma is created by decompression(lessening of pressure)

3.) increasing water content lowers melting point further4.) gasses come out of solution-expands BANG-Soda analogy

ND pg. 158 fig. 6.8

Then

ND pg. 157 fig. 6.6

TWO TYPES OF ACTIVITY

1.) Violent and Explosive a.) Occur at subduction zones. WHY? b.) Mt St. Helens

BECAUSE (ND pg. 153 /fig. 6.3)

1.) more heat with depth

2.) subducting plate has water

3.) asthenosphere maficmaterial mixes with overriding felsic material

4.) mafic turns crystallizessooner leaving felsic materialin liquid. state Courtesy of USGS

TWO TYPES OF ACTIVITY

2.) Passive/Easy Going Flow

a.) hot spots and oceanic ridges WHY?

b.) Hawaii

c.) (ND pg. 153 /fig. 6.3)

BECAUSE1.) they sit above hot

asthenosphere zones

2.) small amount of silica inmafic material

3.) ridges/spreading centers producelow pressure pulling up material.

Courtesy of USGS

Courtesy of USGS

WHY THE DIFFERENCE ERUPTION TYPES?

A. Viscosity of magma1.) Resistance to flow (runny versus sticky/clunky)2.) Water versus honey? Which is more viscous?3.) Plugs up the outlet.

B. Gas content of magma

1.) More gas = more explosivity2.) Dry ice in a bottle example

VISCOSITY: The mobility of magma/lava

1.) TEMPERATURE of magma/lava

1.) Consider cold honey and warm honey.

2.) COMPOSITION of magma/lava

1.) Felsic: Lots of silica more viscous does not flow easily

2.) Mafic: Less silica and is less viscous flows easily.

3.)What is so special about silica? Lets talk.(N.D. pg. 154/Fig. 6.4)

4.) Basalt-mafic Andesite-intermediate Rhyolite-felsic(ND pg. 156/Table 6.5)

VISCOSITY: The mobility of magma/lava

3.) MINERAL CONTENT (this needs to be added topublished notes) 1.) The more solid chunks the slower the flow.

2.) How related to content?

Which will flow easier? Honey or oatmeal. Assumptions?

PASSIVE ERUPTIONS: gas content? Silica content?Plate location?

VIOLENT ERUPTIONS: gas content? Silica content?Plate Location?

Courtesy of USGS

VOLCANIC EXPLOSIVITY INDEX

Determined by

1.) volume of material ejected

2.) altitude the eruption

3.) duration of the major blast

4.) Ranges 0-8

5.) Largest ever VEI=7 Tambora (Indonesia) 1815

ND pg. 167/Table 6.8Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT1.)Characteristic Gases:

a.) most abundant is water vapor (50%-80%)b.) carbon dioxide (CO2) (15%)c.) small amounts of nitrogen, sulfur,

chlorine, carbon monoxide, and hydrogend.) these can be detected in various amounts and

help with understanding volcanos (more later)

Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMITPyroclastics-chunks of rock particles.

Bombs/blocks- BIG bigger than 64mm=6.4cm=about 3in.

Courtesy of USGSCourtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMITPyroclastics-chunks of rock particles.

Lapilli: Rock fragments between 2 and 64 mm(0.08-2.5 in) in diameter that were ejected from a volcano during an explosive eruption

Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMITPyroclastics-chunks of rock particles.

Pele’s Tears: Small bits of molten lava in fountains cancool quickly and solidify into glass particlesshaped like spheres or tear drops called Pele'stears, named afterPele, the Hawaiiangoddess of volcanoes.

Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMITPyroclastics-chunks of rock particles.

Volcanic ash: consists of rock,mineral, and volcanicglass fragments smallerthan 2 mm (0.1 inch)in diameter, which isslightly larger thanthe size of a pinhead.

Not like other ash

Courtesy of USGS

Courtesy of USGS

Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT

Pyroclastics-chunks of rock particles.

Pyrocalstic Flow

1.) Chunks of ash, blocks, etc.2.) Races down slope3.) Can be super hot

*Nuee ardente (glowing cloud)

Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMITPyroclastics-chunks of rock particles.

Lahars: Lahar is an Indonesian wordfor a rapidly flowing mixtureof rock debris and water thatoriginates on the slopes of a volcano

Courtesy of USGS Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT

Lava: Lava is from theItalian word for stream,which is derived from theverb lavare--to wash.

Lava Delta: Lava enteringthe sea often builds a widefan-shaped area of newland called a lava delta.

Courtesy of USGS Courtesy of USGS

WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT

A`a (pronounced "ah-ah") is a Hawaiianterm for lava flows that have arough rubbly surface composed ofbroken lava blocks called clinkers.

Courtesy of USGS

Volcanoes erupt as magma is created (melting) by

begins with higher heat at depth-rises as solid

how can we melt solid rock

a.) *lowering pressure- decompression melting

b.) raising the temp.

c.) increasing water content

Courtesy of USGS

THREE BASIC TYPES OF VOLCANOS

1.) SHIELD VOLCANO (low viscosity, low volatiles,large volume)

A.) Broad gently sloping flanks, large sizeB.) Composed of mafic laba layersC.) Passive eruption-low viscosity lavaD.) Effusive eruption (next slide)E.) Example: Hawaiian Islands

Courtesy of USGS

EFFUSIVE ERUPTION:A.) dominated outpouring lavaB.) not violentC.) lava may be`a`a or pahohoe

THREE BASIC TYPES OF VOLCANOS2.) SCORIA or CINDER CONES(medium viscosity,med. volatiles, small volume)

A.) Steep sides and smallB.) Composed of pyroclastic chunks and

ourpouring of baslatic lava from baseC.) Common on sides of bigger volcanos and in groupsD.) Strombolian-type eruptions (hold on, next slide)E.) Example- Sunset Crater AZ

Courtesy of USGSSunset CraterCourtesy of NPS

STROMBOLIAN ERUPTIONS1.) Intermittent explosion or fountaining of basaltic lava2.) single vent or crater3.) Each episode is caused by the release of volcanic gases4.) typically occur every few minutes 5.) rhythmically or irregularly6.) partially molten volcanic bombs

Courtesy of USGS

THREE BASIC TYPES OF VOLCANOS

3.) COMPOSITE or STRATOVOLCANO (High viscosity,high volatiles, large volume)

A.) Steep flanks and large in size

B.) Different layers of felsicto intermediate lava and pyroclastics(andesitic to rhyolite)

C.) Both passive and violent eruption types

D.) pyroclastic flowscommon (nuee ardente)

E.) Example-Mt. St. Helens 1980and Krakatau 1883 Courtesy of USGS

Pg. 27 ADD Let’s look at patterns of ERUPTION STYLES

VEI COMPOSITION VOLCANO (??viscosity??) TYPE

ICELANDIC 0-1 Basalt/mafic Small shield/plateau

HAWAIIAN 0-1 Basalt/mafic Large shield

STROMBOLIAN1-3 Basalt-andesite Scoria cone

VULCANIAN 2-5 Basalt-rhyolite Scoria-stratovolcano

PLINIAN 3-8 Andesite-rhyolite Stratovolcanoes

CALDERA 3-8 Andesite-rhyolite Caldera

N.S. 164/ Fig. 164

1.) FLOOD BASALTS a.) effusive type of eruptionb.) large sheets of lavac.) form plateaus/huge

flat areasexamples

Columbia PlateauSnake RiverSiberiaIndia

2 TYPES OF FISSURE ERUPTIONSNo volcano cone-like feature

HUGE AMOUNTS OF VOLCANIC MATERIAL

2 TYPES OF FISSURE ERUPTIONSNo volcano cone-like feature

HUGE AMOUNTS OF VOLCANIC MATERIAL

2.) PYROCLASTIC/CALDERAa.) high explosivityb.) no central vent/caldera OR collapsed stratovolcano.c.) High viscosity, high volatiles,

SUPER large volumed.) similar to composite/strato may involve Stratovolcano)

but VERY HIGH VOLUMEExamplesYellowstone Plateau ND. Pg. 177/Fig. 6.35

Snake River Plain Hot Spot “trail”WHAT!?!?!?!?I thought hot spot=Katmai National Monument

Pg 27 add VOLCANO MONITORING

1.) Earthquake Swarms Seismic activity Tiltmeters2.) Ground deformation3.) Changes in gas content (ratios)4.) Groundwater changes (level and temp)

USGS link

Courtesyof USGS

Pg 27 add WARNING SYSTEMS

1.) Like EQ/faults each has its own pattern pre-eruption2.) Quick explosions to slow lava flows.3.) Lahar warning system Lahar warning system: problems?

INCLASS REVIEW Review Link