INTRODUCTION: HOW DO VOLCANOES ERUPT? 1.) Heated material from deep (asthenosphere/mantle)

1. 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 further 4.) gasses come out of solution-expands BANG-Soda analogy ND pg. 158 fig. 6.8 Then ND pg. 157 fig. 6.6

2. 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 mafic material mixes with over riding felsic material 4.) mafic turns crystallizes sooner leaving felsic material in liquid. state Courtesy of USGS

3. 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) Courtesy of USGS BECAUSE 1.) they sit above hot asthenosphere zones 2.) small amount of silica in mafic material 3.) ridges/spreading centers produce low pressure pulling up material. Courtesy of USGS

4. WHY THE DIFFERENCE ERUPTION TYPES? A. Viscosity of magma 1.) 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 explosivity 2.) Dry ice in a bottle example

5. 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)

6. VISCOSITY: The mobility of magma/lava 3.) MINERAL CONTENT(this needs to be added to published notes) 1.) The more solid chunks the slower the flow. 2.) How related to content? Which will flow easier? Honey or oatmeal. Assumptions?

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

8. VIOLENT ERUPTIONS: gas content? Silica content? Plate Location? Courtesy of USGS

9. 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 6.8 Courtesy of USGS

10. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT 1.)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 hydrogen d.) these can be detected in various amounts and help with understanding volcanos (more later) Courtesy of USGS

11. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-chunks of rock particles. Bombs/blocks- BIG bigger than 64mm=6.4cm=about 3in. Courtesy of USGS Courtesy of USGS

12. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-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

13. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-chunks of rock particles. Pele’s Tears: Small bits of molten lava in fountains can cool quickly and solidify into glass particles shaped like spheres or tear drops called Pele's tears, named after Pele, the Hawaiian goddess of volcanoes. Courtesy of USGS

14. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-chunks of rock particles. Volcanic ash: consists of rock, mineral, and volcanic glass fragments smaller than 2 mm (0.1 inch) in diameter, which is slightly larger than the size of a pinhead. Not like other ash Courtesy of USGS Courtesy of USGS Courtesy of USGS

15. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-chunks of rock particles. Pyrocalstic Flow 1.) Chunks of ash, blocks, etc. 2.) Races down slope 3.) Can be super hot *Nuee ardente (glowing cloud) Courtesy of USGS

16. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Pyroclastics-chunks of rock particles. Lahars: Lahar is an Indonesian word for a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano Courtesy of USGS Courtesy of USGS

17. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT Lava: Lava is from the Italian word for stream, which is derived from the verb lavare--to wash. Lava Delta: Lava entering the sea often builds a wide fan-shaped area of new land called a lava delta. Courtesy of USGS Courtesy of USGS

18. WHAT COMES OUT OF VOLCANOS? VOLCANO VOMIT A`a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. Courtesy of USGS

19. 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

20. THREE BASIC TYPES OF VOLCANOS 1.) SHIELD VOLCANO (low viscosity, low volatiles, large volume) A.) Broad gently sloping flanks, large size B.) Composed of mafic laba layers C.) Passive eruption-low viscosity lava D.) Effusive eruption (next slide) E.) Example: Hawaiian Islands Courtesy of USGS

21. EFFUSIVE ERUPTION: A.) dominated outpouring lava B.) not violent C.) lava may be`a`a or pahohoe

22. THREE BASIC TYPES OF VOLCANOS 2.) SCORIA or CINDER CONES(medium viscosity,med. volatiles, small volume) A.) Steep sides and small B.) Composed of pyroclastic chunks and ourpouring of baslatic lava from base C.) Common on sides of bigger volcanos and in groups D.) Strombolian-type eruptions (hold on, next slide) E.) Example- Sunset Crater AZ Sunset Crater Courtesy of NPS Courtesy of USGS

23. STROMBOLIAN ERUPTIONS 1.) Intermittent explosion or fountaining of basaltic lava 2.) single vent or crater 3.) Each episode is caused by the release of volcanic gases 4.) typically occur every few minutes 5.) rhythmically or irregularly 6.) partially molten volcanic bombs Courtesy of USGS

24. 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 felsic to intermediate lava and pyroclastics (andesitic to rhyolite) C.) Both passive and violent eruption types D.) pyroclastic flows common (nuee ardente) E.) Example-Mt. St. Helens 1980 and Krakatau 1883 Courtesy of USGS

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

26. 2 TYPES OF FISSURE ERUPTIONS No volcano cone-like feature HUGE AMOUNTS OF VOLCANIC MATERIAL 1.) FLOOD BASALTS a.) effusive type of eruption b.) large sheets of lava c.) form plateaus/huge flat areas examples Columbia Plateau Snake River Siberia India

27. 2 TYPES OF FISSURE ERUPTIONS No volcano cone-like feature HUGE AMOUNTS OF VOLCANIC MATERIAL 2.) PYROCLASTIC/CALDERA a.) high explosivity b.) no central vent/caldera OR collapsed stratovolcano. c.) High viscosity, high volatiles, SUPER large volume d.) similar to composite/strato may involve Stratovolcano) but VERY HIGH VOLUME Examples Yellowstone PlateauND. Pg. 177/Fig. 6.35 Snake River Plain Hot Spot “trail” WHAT!?!?!?!?I thought hot spot= Katmai National Monument

28. USGS link Pg 27 add VOLCANO MONITORING 1.) Earthquake Swarms Seismic activity Tiltmeters 2.) Ground deformation 3.) Changes in gas content (ratios) 4.) Groundwater changes (level and temp) Courtesy of USGS

29. Pg 27 add WARNING SYSTEMS 1.) Like EQ/faults each has its own pattern pre-eruption 2.) Quick explosions to slow lava flows. 3.) Lahar warning system Lahar warning system: problems?

30. INCLASS REVIEW Review Link