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Dancing with Volcanoes Bethany Ehlmannson Gillian Galford.

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Presentation on theme: "Dancing with Volcanoes Bethany Ehlmannson Gillian Galford."— Presentation transcript:

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2 Dancing with Volcanoes Bethany Ehlmannson Gillian Galford

3 The Hawaiian Archipelago  North

4 Type of Volcanoes Composite volcanoes have steep slopes Hawaii’s shield volcanoes slope very gradually

5 The Big Five Mauna Loa- largest volcano on the planet 4 km above sea level (covers area equivalent to 85% of all other Hawaiian Islands combined) erupted in 1984 Mauna Kea Haulalai- grew above sea level 300,000 years ago, eruptive period in 18th century. Many earthquakes in 1929 Kilauea-one of the most active volcanoes in the world, originally just though a satellite to Mauna Loa Kohala Mauna Loa- largest volcano on the planet 4 km above sea level (covers area equivalent to 85% of all other Hawaiian Islands combined) erupted in 1984 Mauna Kea Haulalai- grew above sea level 300,000 years ago, eruptive period in 18th century. Many earthquakes in 1929 Kilauea-one of the most active volcanoes in the world, originally just though a satellite to Mauna Loa Kohala Mauna Loa Hualalai Mauna Kea Kilauea Kohala

6 Basaltic Composition Range Alkali –high Na 2 O & K 2 O content Tholeiitic –low alkali content Varying SiO 2 (silica) content

7 Preshield- infrequent eruptions, small volcanoes alkalic basalt (meaning???) although becoming less alkalic with time 2. Shield- forming frequent eruptioins, large volumes of basalt e.g. Kilaeua, Mauna Loa 3. Postshield after shield construction cap of different lavas from vents along rift zone e.g. Hualalai, Kohala 4. Rejuvenated Follows Ma period of quiescence infrequent small scale eruptions from vents found on Kauai Preshield- infrequent eruptions, small volcanoes alkalic basalt (meaning???) although becoming less alkalic with time 2. Shield- forming frequent eruptioins, large volumes of basalt e.g. Kilaeua, Mauna Loa 3. Postshield after shield construction cap of different lavas from vents along rift zone e.g. Hualalai, Kohala 4. Rejuvenated Follows Ma period of quiescence infrequent small scale eruptions from vents found on Kauai Life of a volcano (4 stages of evolution and growth) Preshield –Loihi Shield-forming –Mauna Loa, Kilauea Post-shield –Mauna Kea, Hualalai, Kohala Rejuvenation –Kauai

8 Pillow lava Submarine basaltic eruptions Repeated oozing and quenching of hot basalt formed by repeated oozing and quenching of hot basalt. First, a flexible glassy crust forms around newly extruded lava, forming a pillow. Pressure builds until crust breaks and new basalt extrudes like toothpaste, forming another pillow. This sequence continues until a thick sequence may be deposited. v formed by repeated oozing and quenching of hot basalt. First, a flexible glassy crust forms around newly extruded lava, forming a pillow. Pressure builds until crust breaks and new basalt extrudes like toothpaste, forming another pillow. This sequence continues until a thick sequence may be deposited. v

9 Extinction Surface weathering Slow submergence Coral reefs and atolls The pacific crust to too weak to support the large volcanoes and so it becomes “downbowed” to achieve isostatic balance. Coral is a calcareous algae-- plants that deposit calcium carbonate. They often form around sediment-rich river mouths (connection to eroding island). An atoll is a roughly circular reef with no land matter in the center Good picture on 287 Volcanoes in the Sea The pacific crust to too weak to support the large volcanoes and so it becomes “downbowed” to achieve isostatic balance. Coral is a calcareous algae-- plants that deposit calcium carbonate. They often form around sediment-rich river mouths (connection to eroding island). An atoll is a roughly circular reef with no land matter in the center Good picture on 287 Volcanoes in the Sea

10 Surface Formations This is the intro to the next section-- we will make it appear that way visually

11 Pahoehoe vs. A’a Pahoehoe can become a’a due to cooling, gas loss, and crystallization

12 Columnar basalt Slow cooling Hexagonal columns based on atomic arrangement Result of thermal or tectonic stress Thin sheets of basalt are laid down. Eventually all are cooled, but tensile strength is surpassed (ability of rock to resist being pulled apart). Cracks spontaneously form at many points on isothermal surface. Three pronged cracks at angles of 120 degrees (equilibrium config.). Cracks propagate, form stable hexagon. With continued cooling and contraction, cracks propagate inward with region of isothermail cooling, creates 3D.

13 The Summit Common Features: a caldera spatter cones cinder cones

14 Spatter Cones

15 Ejecta Tephra Bombs Spherical Fusiform Cow dung Vesicles in an ash particle

16 Pele’s tears Limu o Pele Pele Pele’s Hair

17 Rocks! Most abundant single mineral is feldspar, esp. plagioclase Olivine and augite are common dark minerals –tiny grains of magnetite can separate in low grade metamorphism Xenoliths of periodite

18 Seismic Chaos

19 Cracks in the Earth Fissures Rift Zones Faults

20 Earthquakes Thousands of earthquakes per year Most can’t be felt, a few cause mild damage Causes: >Magma movement -causes little damage except near the site -may be indicators of eruptions >Structural weakness

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22 Joe vs. the Volcano When humans and volcanoes collide...

23 Keoua’s ill-fated expedition against Kamehameha.

24 What are the Hazards? Lava flows Poor air quality

25 Tourism

26 But oh no! Before After

27 Safety Precautions for Working Around Volcanoes PLEASE READ CAREFULLY-YOUR LIFE MAY DEPEND ON IT Viewing Lava Safely - Common Sense is Not Enough What are the Volcanic Hazards Facing you? Bench collapse can kill Tephra jets & littoral fountains hurl hot lava Steam blasts toss rocks Vog - Acid fumes and glass particles can irritate eyes and lungs Scalding waves burn In the event of a strong earthquake which may cause tsunami, run for high ground immediately

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