Volcanism and Other Igneous Processes

1. Volcanism and Other Igneous Processes 1

2. On Sunday, May 18, 1980, the largest volcanic eruption to occur in North American historic times transformed a picturesque volcano into a decapitated remnant. On this date in southwestern Washington State, Mount St. Helens erupted with tremendous force. • What happened?? • Approximately 1 km3 of ash erupted. • Summit decreased by 1,350 feet. • Claimed 59 lives • Ash propelled 11 miles into the atmosphere. • Ash covered surrounding areas of Yakima, Tri-cities, and • northern Oregon for 3 days – Noon felt like night. • Feb. 1981- highest birth rate in Portland and surrounding areas –TRUE FACT • Advice from the authorities: • If there is another major eruption, put your head between your • legs and kiss your ash goodbye! Before After Mt. St. Helens 2

3. The “buzzword” is VISCOSITY What is viscosity? Viscosity = how well a material flows more viscous – flows very slowly (high viscosity) less viscous – flows quickly (low viscosity) Does glass have viscosity? 5

4. I geology class Discuss with a friend: • What is viscosity? • Provide an example of a high • viscous and low viscous material. I will get an A on my exams and quizzes

5. Why do volcanoes have different eruptive styles??? • high viscosity • high SiO2 • felsic • “pasty” • explosive 4 • Factors influencing eruptions • dependant on the magma’s viscosity • high viscosity –”pasty” explosive • low viscosity –”fluid” flows easily • Factors influencing viscosity • Temperature of magma • T viscosity = fluid flow • T viscosity = pasty flow A • low viscosity • low SiO2 • mafic • “fluid” • non-explosive • Chemical composition • SiO2 content (high or low) mafic composition: (50% SiO2)=“fluid” flow intermediate comp.: (60% SiO2) felsic composition: (70% SiO2) =“pasty” flow B

6. Dissolved gasses – influencing the movement of magma (volatiles – water, CO2, SO2….) Silica content and volatiles erupt two types of materials: Gas charged expands 100 times its volume Gas charged lava expands 100 times its volume lava fountains very explosive lava flows fluidly Volatiles migrate upwards with difficulty volatiles easily migrate upward 6 magma low in SiO2 magma high in SiO2

7. sulfur dioxide SO2 > 1% 5% Carbon dioxide water vapor 15% 70% 5% volatiles • Dissolved gasses (volatiles) • 1-6% of total magma wt. • contributes to atmosphere Magma chamber 7

8. Types of Basaltic Lava Flows (low silica (SiO2) content) Pahoehoe Aa • very fluid, thin, • broad sheets • flows 10-300 km/hr • (30-900 ft/hr) • high volatile gas content • smooth “skin,” ropey • type flow • very “pasty,” sticky, • thick, cool flows • flows 5-50 m/hr • (15-150 ft/hr) • low volatile gas content • rough, blocky, sharp, • angular type flow 9

9. Pyroclastic materials Bombs Ash Volcanic Bombs Nuee-Ardente Lahars Lahars mud flows Ash • Ryholitic magmas • high silica • very explosive • thick, pasty • high viscosity • pyroclastic ejections Nuee-Ardente 10

11. Volcano Morphology

12. I geology class Discuss with a friend: 3. What two factors affect a volcanoes viscosity? 4. What is meant by volatiles? 5. Describe the differences between an aa and pahoehoe lava flow. 6. What are pyroclastic flows and provide at least three examples?

13. Three types of Volcanoes • Volcano type is dependant on • SiO2 content. Shield Composite (stratovolcano) Explain the differences. Cinder cone 14

14. Shield Volcano - Hawaii Broad, low angle flanks • Shield Volcanoes • Hawaiian Islands, Iceland, Galapagos Islands • commonly rise from the deep ocean floor • formed by the accumulation of fluid basaltic flows • low silica content (basaltic composition) • low viscosity • less than 1% pyroclastic debris • non-explosive eruptions • pahoehoe flows • aa flows 15

15. Stratovolcano Nuee Ardente gas cloud • Composite Cones (stratovolcanoes, stratacomposite) • Western U.S. coast, Western South American coast, Japan • typically form in the ocean along continent convergent boundaries • found along the ring of fire Steep high angle flanks Pyroclastics • formed from layering deposits of • ash, lava, and pyroclastic flows • high silica content (70%)- (Rhyolitic • composition) • high viscosity flows • abundant pyroclastic activity • deadly airborne debris • explosive eruptions – very hazardous

16. Cinder Cones (Scoria Cones) • exist all over the earth’s surface (by the 1000’s) • characteristic of volcanic fields (Flagstaff, AZ., approx 600) Very high, steep angled flanks 30-40 degrees Averages 100 ft – 1000 ft high

17. Formed by gas rich basaltic flows (low viscosity, low silica) producing small sized material. Common rock scoria and volcanic glass with abundant vesicular textures Single eruptive episode lasting a short time – 95% formed in less than 1-year. Composed of scoria and loose pyroclastic material Cinder cones can form as parasitic type cones.

18. The Famous Paricutin Cinder Cone • 200 miles west of Mexico City • erupted in a corn field, 1943 – grew 130 feet in 1-day • June, 1944, 30-ft thick aa flows buried the village • 1952, volcano ceased! Paricutin Cinder Cone

19. Cinder Cones 20

20. I geology class Discuss with a friend: 7. Describe various characteristics that distinguish differences between composite, shield, and cinder cone type volcanoes. I will get an A on my exams and quizzes

21. Other Volcanic Landforms • Calderas • Volcanic Fissures • Exposed Volcanic Pipes and • Necks

22. Caldera (cooking pot) • large depressions in excess • of 1-mile diameter • Formed the following ways • collapse of the summit • following an explosive silica • rich eruption (Crater Lake) • collapse of a shield volcano • from drainage of central • magma chamber (Hawaiian • Islands) • collapse of a large area from • the discharge of colossal • volumes of high silica rich • pyroclasitc materials. Wizard Island

23. collapse of a shield volcano • from drainage of central • magma chamber (Hawaiian • Islands)

24. collapse of a large area from • the discharge of colossal • volumes of high silica rich • pyroclasitc materials.

25. I see extensive lava flows, but where are the volcanoes? • Fissure type eruptions and lava plateaus • very fluid basaltic lava erupted from fractures in the earth’s • crust • lava fountains along “linear” fractures spreading out over • wide areas • extrudes voluminous amounts of low silica basaltic lava • single flows can travel 100’s of kilometers • Columbia River basalts • 17 m.y. flows • very extensive –single flows from • Idaho to Portland, Ore. • 1 mile thick in SW Washington Study Area 21

26. Columbia River Basalts 1-mile

27. Lava Domes • “thick” silica rich lavas (very rhyolitic in composition) • “squeezed” out of the volcanic vent • forms slowly over time • can form along volcano flanks Lava Dome (plugged dome)

28. Volcanic Pipes and Necks (diatreme) • diatremes extend to depths of • 200 km (125 miles) • magma ascends rapidly with • little alteration • characteristic of high P/T • minerals --- diamonds • considered “windows” to • the Earth’s interior • Best known diatremes are the • Kimberlite diatremes of • South Africa --- diamond • bearing diamond

29. Shiprock, New Mexico • stands 420 meters (1380 feet) • Ryholitic remnants of a volcanic neck and dike • Volcanic neck and dike more resistant rock

30. I geology class Discuss with a friend: 8. Define the following volcanic characteristics: caldera Volcanic fissures diatremes I will get an A on my exams and quizzes

31. Divergent plate volcanism Plates separate resulting from basaltic magma ascending into fractures. Shield type volcanoes form ridges and mountains below the ocean. • Very fluid eruptions • Less than 50% SiO2 content • Shield type volcanoes • Basalt rocks 23

32. Ocean – Ocean plate convergence • Very fluid eruptions • Less than 50% SiO2 • Shield type volcanoes • Basalt rocks Oceanic plate subducts beneath oceanic plate. Melting subducted plate ascends upward forming shield type volcanoes in the form of island arc systems “mountainous arcs” that rise above the ocean floor. – Japan, Aleutian Islands 24

33. Baker Ocean to Continent convergence Rainier Pacific Plate St. Helens Adams Oceanic plate is subducted beneath continental plate. Melting plate ascends upward mixing with continental material. Hood Jefferson Three Sisters Newberry Volcano Crater Lake North American Plate • High SiO2 – High viscosity • explosive volcanoes • “pasty” lava flows • composite type volcanoes • andesite/rhyolite rocks McLaughlin Medicine Lake Volcano Shasta Lassen Peak 25

34. Ring of Fire • pattern of EQ and volcanism • marks converging plates

36. I geology class Discuss with a friend: • 9. For each plate tectonic boundary • (divergent, convergent), describe • the type of volcano and eruption • style associated with each. I will get an A on my exams and quizzes

37. Living with Volcanoes • 10% of the Earth’s population is situated near • volcanoes. • Seattle, WA; Mexico City, Mexico; Tokyo, Japan; • Naples, Italy; Quito, Ecuador • And, volcanoes are destructive as well as • unpredictable! Volcanic Hazards

38. The ranking of volcanic hazards • Pyroclastic flows – composite volcanoes • mixtures of gas, ash, pumice • temperatures of 8000C • pyroclastic clouds – Nuee-Ardente clouds • Lahars, huge mudflows moving down pre-existing • stream valleys • reach speeds up to 100 km/hr (60 mi/hr) • potential threat with inactive volcanoes • high potential with glaciated volcano summits • Rapid collapse of the crater or areas within the flanks • creates rapid mass wasting events • Explosive eruptions (typical of composite volcanoes) • ash clouds endanger folks – 100’s miles away • 1989 Bowing 747 near crash! – Alaska Volcano

39. Nuee-Ardente

40. Old lahars

42. I geology class 10. How would one describe a volcanic hazard? 11. Describe the number one volcanic hazard. 12. Define lahars. I will get an A on my exams and quizzes

43. Monitoring Volcanic Activity • Monitoring volcanic activity is typically • measured by observing the movement of • ascending magma. • measuring the frequency of volcanic EQ’s • volcanoes that have historically erupted in • the past are equipped with seismographs • increase volcanic EQ’s a precursor to an • eruption • expansion of the magma chamber, changing the • size and volcanic topography • rising magma that builds the volcano proves • as a precursor • uses of remote sensing equipment

44. Monitoring Volcanic Activity • changes in the pre-eruptive volcanic gasses • increases in SO2 gas emissions • increases in ground temperatures • surface temperatures rise from • heat radiation of the ascending magma Remote sensing equipment used to measure any changes in the South Sister Volcano, Cascade Range, Ore

46. I geology class Discuss with a friend: 13. Describe the four ways that volcanologists monitor volcanoes? (ascending magma) I will get an A on my exams and quizzes