10-2) The Nature of Volcanic Eruptions

Question 1

what are the factors affecting eruptions?

Answer 1

viscosity and dissolved gases

Question 2

what is viscosity?

Answer 2

the substance’s resistance to flow

Question 3

high viscosity ____ flow?
low viscosity ____ flow?

Answer 3

resists
easily

Question 4

more viscous is?
less viscous is?

Answer 4

thick and more violent
thin gentle eruptions

Question 5

more silica =

Answer 5

greater viscosity, more violent

Question 6

granitic magma has…?

Answer 6

higher silica, thickness causes pressure build up which leads to explosive eruptions.

Question 7

basaltic magma has/is…?

Answer 7

less silica, less viscous, quiet eruptions

Question 8

what are dissolved gases?

Answer 8

gases trapped in the magma provide the force to propel lava out the vent

Question 9

explain what happens when carbon dioxide gas is dissolved in the liquid? (like a soda can)

Answer 9

it expands and forms bubbles that rush to surface, under the surface gases are under great pressure. as magma approaches surface pressure is greatly reduced. when a volcano erupts it pushes magma up and remaining gases bubble out.

Question 10

hot basaltic lava is?

Answer 10

usually fluid, (low silica, low viscosity), runs down sides of volcanoes

Question 11

what are the two types of basaltic lava?

Answer 11

Pahoehoe lava - hotter, fast-moving basaltic lava “twisted rope”, smooth surface. Aa lava - cooler, slower-moving, “spiny” rough surfaces.

Question 12

what are pyroclastic materials?

Answer 12

particles produced in volcanic eruptions, cools quickly and hardens into different sizes.

Question 13

explain the pyroclastic materials from smallest to largest.

Answer 13

volcanic ash (smallest pieces), cinders (pebble-sized), blocks (larger-sized), bombs (blocks as glowing lava)

Question 14

what are the volcanic hazards?

Answer 14

lava flows, volcanic ash, pyroclastic flows, and mudflows

Question 15

what is a pyroclastic flow?

Answer 15

scorching mixture of glowing volcanic particles/gases that sweeps fastly down volcano’s flanks

Question 16

what is lahar?

Answer 16

when water-soaked volcanic ash and rock slide rapidly downhill, ice and snow melted by an eruption/heavy rains can trigger it

Question 17

what is a crater?

Answer 17

steep bowl-shaped area that may form at the top of the volcano around central vent

Question 18

what is lava flow?

Answer 18

area covered by lava as it pours out of a vent. obsidian - lava cools very quickly (smooth/glossy). pumice - gases trapped in fast cooling lava

Question 19

explain shield volcanoes! what type of eruption, what lava/magma, how well it flows, shape.

Answer 19

quiet eruption, basaltic lava, flat layers that are fluid like and flows well (low silica), layers harden on top of each other and build up broad volcanoes, gently sloping sides

Question 20

explain cinder cones! what type of eruption, what lava/magma, how well it flows, shape.

Answer 20

explosive eruption, high viscosity (high silica), basaltic lava, flow slowly, lava cools and hardens into tephra, vary in size. steep-sided.

Question 21

explain composite cones! what type of eruption, what lava/magma, how well it flows, shape.

Answer 21

vary between quiet and violent, most dangerous, alternating layers (between shield and cinder), andesitic magma, tall cone-shaped, found in subduction zones

Question 22

volcanic activity can volcanic landforms like?

Answer 22

calderas, volcano necks, and lava plateaus

Question 23

what are calderas?

Answer 23

huge hole left by collapse of a volcanic mountain. enormous eruption empties vent and chamber and mountain becomes hollow and collapses.

Question 24

what are volcanic necks?

Answer 24

when magma hardens in a volcano’s pipe. softer rock of tephra around pipe wears away.

Question 25

what are lava plateaus?

Answer 25

high relatively level landforms, erupts from cracks in crust instead of through a vent. thin, low viscosity, hot basaltic lava travels before cooling.