Volcanoes

Volcano – opening in the earth where magma can rise to the surface They can be: Active – able to release magma and gases at any time Dormant – do not release magma at any time currently Extinct – no magma available

Parts of a Volcano Magma chamber – collection of magma underground Conduit – passage from chamber to vent Crater/Central vent – opening at the top Side vent – opening on the sides Lava – magma above ground Gases/Ash/Pyroclastic materials

Formation of Volcanoes Rock underground is melted to form magma Magma rises to the surface and exits the earth – process called volcanisms On the surface it exists through vents - it is now called lava The lava collects around the vent and sides of the opening

Volcano Location Most are at: Divergent boundaries – at mid oceanic ridges Convergent boundaries – at subduction zones Rest are at: Hot spots – thin areas of crust in the middle of the plate magma melts through Largest concentration – at the Pacific Ring of Fire

Forming Volcanoes

Volcanic Island at Hot Spots

Types of Magma Magma has different consistencies based on what is in it Malfic magma – rich in magnesium and iron Dark, thin (low viscosity) Felsic magma – rich in silicates Light, thick (high viscosity)

Types of Eruptions Quiet - caused by thin magma with little gases The lava gently flows out of the earth Types of lava include: Pahoehoe lava – lava that hardens smooth and ropey Aa lava – lava that hardens with sharp edges

Types of Eruptions Violent Eruptions- Caused by thick magma with lots of gas Releases gases, lava, and pyroclastic materials such as: Volcanic ash – smallest pieces Lapilli – small rocks that tend to fall near vent Volcanic bombs – molten rock that starts to cool in the air Volcanic blocks – pieces of the volcano that have broken off

Types of volcanoes Shield – broad, gentle slopes, and made of lava Gentle eruptions Cinder – steep sides, made of pyroclastic materials Violent eruptions Composite – made of alternating layers of lava and pyroclastic materials Both types of eruptions

Shield Volcano

Cinder Volcano

Composite Volcanoes

After an Eruptions Volcano can form: Crater – can fill with water to create a lake – called Crater lake Caldera – depression formed when the sides of a volcano collapse into an empty magma chamber

What If Magma Stays Below Ground? If cool enough - It can harden into igneous rock below ground – called plutons Small horizontal – called sills Small vertical – called dikes Large collections – called batholiths

Predicting Volcanoes Use signs like: Increased earthquake activity – using seismometer Bulges in the surface – as magma rises – using a geodiameter and tiltmeter Increase in gases released Changes in gas composition Eruption history

Volcanoes – Are they good or bad? Good: Add carbon dioxide and water to atmosphere Create new land Add nutrients to environment Bad: Release poisonous gases Destroy property and crops Can create tidal waves and mudslides Affect the weather