Volcanic Eruptions Will it flow or will it

Volcanic Eruptions Will it flow or will it blow? Types and Products

Explosive Eruptions • Less common • More destructive • Mostly produce clouds of hot ash, gas and rock fragments shoot rapidly out of a volcano. • Ash can reach upper atmosphere and stay for years, blocking sunlight • Can blast billions of tons of material • Eg Mount St. Helens

Effusive or Nonexplosive Eruptions • More common • Less destructive • Mostly lava flowing over the Earth’s surface • Most rock on ocean floor was produce by nonexplosive eruptions (Oceanic Volcanoes)

Magma Composition Determines type of Eruption: • Viscosity and dissolved gasses determine the violence of the eruption. • Viscosity is determined by mineral and water composition More water – lava will be less viscous, flows easier (less violent) More gas - means more bubbles (more violent eruptions) More silica – more viscous lava, slower flowing, traps gas (more violent)

Mafic/Basaltic Lava Flow • Darker in colour • high iron and magnesium • low silica content, • Low viscosity due to • Rapid (up to 100 km/hr), Long distance flow – up to 100 s of km • less explosive eruptions - Mafic magma allows gases to escape more easily • Form much of ocean crust • (P and a’a)

Felsic or Rhyolitic Lava Flows • Lighter in colour • Low iron, and magnesium • Highest silica content, • most viscous, rarely flows • Plugs vent as a lava dome • Lower temperature • gases do not escape easily, leading to more explosive eruptions. • Commonly found in continental crust

Intermediate/Andesitic Lava Flows • Intermediate to high viscosity (more Silicon than basalt) moderate amounts of silica, Fe and Mg • Mound near vent, flow slowly • Outer crust fractures, creating rubble • Eg. Mount St. Helens

What comes out of a volcano? Eruptive Material: Lava Flows, Pyroclastic debris, volcanic gases

Eruptive Material: • Gases • Lava • Ash • Tephra (solid airborne fragments).

Gases in Magma • Water vapor, Carbon dioxide, Sulfur, Hydrogen • As magma comes to the surface, the gases are released as bubbles, making the eruption more explosive.

Type of lava formed depends on. . . • Temperature • Composition (minerals and gases) • How it cools

Pahoehoe If lava cools slowly and does not move too fast, it forms smooth ropey lava called pahoehoe.

A’a lava • If lava cools quickly and moves fast it can tear into chunky jagged pieces called a’a. • More common

Blocky Lava • Cool, stiff lava that does not travel very far from the volcano forms piles of rocks with sharp edges. • Larger blocks than a’a lava, and have smoother surface.

Pillow Lava • Forms rounded lumps that look like pillows when it cools underwater.

Columnar • Giant’s Causeway, Northern Ireland.

Tephra – solid airborne fragments • Generic term for any airborne pyroclastic material (solid) • Classified according to size

Volcanic Ash • fine-grained fragments < 2 mm in diameter • Volcanic ash forms when gases trapped in magma or lava form bubbles. • When the bubbles explode, they create millions of tiny pieces.

Volcanic Ash on Plymouth, Monserrat after 1995 Eruption

Hazards Associated with Ash • Daylight turns into darkness. • Roofs may collapse from added weight. • Machinery and vehicles will be abraded. • Farmland will be covered. • Roads will be slippery, blocked, or blocked. • Power systems may shut down. • Waste-water systems may clog. • Gutters may fill and collapse.

Lapilli (Latin for “little stones) Lapilli are small bits of lava that harden before they hit the ground. Pea- to walnut-size pyroclasts (2 -64 mm) All types of lava produces lapilli. All types of volcanoes produce lapilli

Lava Bombs • Large (< 64 mm) blobs of lava ejected while still molten, gaining a streamline shape, harden in the air and cool before they reach the ground. • More rounded

Lava Blocks • Angular fragments ejected when already solid. • larger than 64 mm in diameter • Can be as big as houses

Pyroclastic Flows • Very hot (700ºC), • Very fast (100 km/h), • Current of gas and tephra. • Very dangerous (can destroy everything in its path). • can extend several km from the volcano, and devastate life and property within their paths. • A pyroclastic flow from the eruption of Mount Pinatubo is shown in the figure below. • https: //www. youtube. com/watch? v=EZd. Fqvnz. Cl. U • Play only 1 st minute

Homework • Volcano WS, Questions #1 -7 • Top 10 volcanoes ready to blow: 7. 5 min • https: //www. youtube. com/watch? v=zq. Gsgvc. BSA 4 • Ted Ed colossal consequences 4. 5 min • https: //www. youtube. com/watch? v=h. DNlu 7 Qf 6_E • Research Volcano Project

Other Links • Good description of types of eruptions: • http: //volcano. oregonstate. edu/volcanic-cones-and-eruptionslesson-8 • List of volcanoes: • http: //content. time. com/time/specials/packages/completelist/0, 2 9569, 2014572, 00. html • Video • https: //www. youtube. com/watch? v=RRCQS_Oaevs • https: //www. youtube. com/watch? v=03 NBObzj. J 7 c

Moai of Easter Island It is one of only fourteen moai made from basalt, the rest are carved from the island’s softer volcanic tuff.