Chapter 10 section 1volcanoes and other igneous

activity

viscosity

• Is a substances resistance to flow

• Temperature on viscosity easy to see

• Mobility of lave strongly affected by temperature

• Chemical composition of magma has more important affect on the type of eruption

• The more silica in magma the greater it is viscosity

– High silica means slower flow

– Lower silica faster flow

Dissolved gasses

• During eruption ,the gasses trapped in magma provide the force to eject molted rock

• Vent-an opening to the surface.

• Mostly water vapor and carbon dioxide

• Fluid basaltic magma allows expanding gases to bubble upward and escape easily

• Most are quite

Lava flow

o Most lava is very fluid because of the low amount of silica

o Flow rate at 10 to 300 meters per hour

o Silica rich lava is slower

o When basaltic lava harden it makes a smooth skin that wrinkles known as Pahoehoe

o Aa is another form of basaltic lava

o Rough jagged blockso With dangerously sharp edges

Pyroclastic materials

• When lava is extruded • Some ejected lava may land

near the vent and forma cone shape

• Wind will carry small partials a long way

• The fragment ejected during eruption range in size from very fine dust and volcanic dust to pieces that weigh several tons

Type of volcano

• They’re three main volcanic type– Shield volcanoes– Cinder cones – Composite cones

• Anatomy of a volcano – Activity often begins

when a fissure or develops in the crust

Shield volcanoes

• Are produced by the accumulation of fluid basaltic lavas

• Shape of broad slightly domed

• Most have grown from the deep of the ocean

• Including Hawaiian island and Iceland

Cinder cones

• Ejects lava which hardens in the

air • Range in size from fine ash to

bombs but mostly lapilli

• Produce gas rich basaltic magma

• Come in simple shapes

• Shape determined by steep-sided slope

• Last only a couple of weeks

• because of short life span cinder cones are small between 30 to 300 miters

Composite cones

• Most beautiful but also most dangerous

• Also known as stratovolcanoes

• Located in relatively narrow zones

– Pacific ocean (ring of fire)• Cascade range, mount. St.

Helen, mount. Rainier, and mount. garibaldi

• Most activity are located in the curved belts of volcano island

Lava plateaus

• Greatest volume of volcano excrete from fissures

• Columbia plateau was formed this way

• Numerous fissure erupted their

• Some go up to50 miters thick but some only 1.6 miters thick