1. VOLCANISM & Igneous Activity

4. VOLCANISM Lava = Magma at earth surface –Silica content controls “explosiveness” Pyroclasts = Fragments of rock due to explosion- Ash falls (pumice); Volcanic Bombs (scoria) Lava flows Extrusive rocks Volcano

6. VOLCANISM Lava = Magma at earth surface –Silica content controls “explosiveness” Pyroclasts = Fragments of rock due to explosion- Ash falls (pumice); Volcanic Bombs (scoria) Lava flows Extrusive rocks Volcano

13. Effects on Humans Growth of Hawaii –1980’s & 90’s 1.5 billion cubic meters Geothermal energy- New Zealand; California Effect on climate- 1816 “year without summer” Volcanic catastrophies –Mt. St. Helens 1980 –Vesuvius 79 AD –Krakatoa 1883 –Crater Lake 6,600 y.b.p.

16. Mount St. Helens Northern flank bulged at 1.5m/day All vegetation stripped for 10km w/in seconds $100s millions in damage 63 people died Damage minimized due to prior planning by USGS and governor

24. Extrusive Rocks & Gases Scientific study of volcanism Gases –Primarily H 2 O –Also CO 2, SO 2, H 2 S, HCl Gases & pyroclastics –Ashfall –Pyroclastic flow

29. Extrusive Rocks Textures –Fine-grained (smaller than 1 mm) –Glassy- Obsidian –Due to rapid cooling (mainly) high viscosity –Porphyritic Phenocrysts –Due to trapped gas Vesicles Scoria Pumice

32. VOLCANOES Volcanoes are cone-shaped Vent Crater Flank eruption Caldera Types: –Cinder Cone, Shield, Composite

35. VOLCANOES Types: –Cinder Cone, –Shield, –Composite

36. CINDER CONES Formed of pyroclastics only Steep sides- ~30 degrees Relatively small Short duration of activity

38. SHIELD VOLCANOES Low viscosity lava flows –Low silica magma- mafic –Basalt Pahoehoe Aa Gently sloping flanks- between 2 and 10 degrees Tend to be very large Spatter Cone- minor feature

42. COMPOSITE VOLCANO Alternating pyroclastic layers & lava flows Slopes intermediate in steepness Intermittent eruptions over long time span Mostly Andesite Distribution –Circum-Pacific Belt (“Ring of Fire”) –Mediterranean Belt

44. COMPOSITE VOLCANO Alternating pyroclastic layers & lava flows Slopes intermediate in steepness Intermittent eruptions over long time span Mostly Andesite Distribution –Circum-Pacific Belt (“Ring of Fire”) –Mediterranean Belt

46. VOLCANIC DOMES Forms above a volcanic vent Viscous lava –Usually silica-rich (or cooler magma) Associated with violent eruptions

48. Lava Flows AA –rubbly surface, broken, jagged Pahoehoe –ropy surface

51. LAVA FLOODS Mafic lava- solidifies to basalt Fissure flows –Plateau basalts Columnar structure or jointing

58. SUBMARINE ERUPTIONS Pillow basalt

60. INTRUSIVE BODIES (STRUCTURES) Bodies that solidified underground-Plutons Volcanic neck- shallow intrusion Fills cracks (joints)- tabular bodies – DIKE- If no layering in country rock If country rock is layered- Discordant – SILL- less common Concordant- parallel to layering in country rock

64. INTRUSIVE STRUCTURES Plutons BATHOLITH- – Large intrusive body – Exposed in an area greater than 100 square Km. – Coalesced smaller plutons smaller bodies are called STOCKS Batholiths a gathering of smaller blobs Magma moves upward from depth as diapirs