despite the high temperature in the mantle, most of the layer remains solid due to extreme pressure...
TRANSCRIPT
Target #16- I can summarize the conditions needed for magma to form
• Despite the high temperature in the mantle, most of the layer remains solid due to extreme pressure–Magma: liquid rock produced under
Earth’s surface
Target 16- cont.
• Melting Point: the temperature at which a substance will change from a solid to a liquid
• Magma can form in three ways– Temperature rises above the
melting point of rock– Pressure decreases lowering
the melting point of rock– Addition of fluids, like water,
can decrease the melting point
Target 17- I can define volcanismTarget #18- I can differentiate between magma
and lava
• Volcanism: any activity that includes the movement of magma and gases toward or onto Earth’s surface–Magma rises because it is less dense
than the surrounding rock• magma that flows onto Earth’s surface is
called lava• Flows from an opening, or vent
Target #19- I can differentiate between mafic and felsic magma
• Mafic: magma that is rich in magnesium and iron– Dark in color– Makes up oceanic
and continental crust
• Felsic: magma that is rich in feldspar and silica– Light in color–Makes up
continental crust only
• When magma erupts from a volcano and then cools & hardens, it forms an igneous rock
Target #20- I can describe viscosity
• Viscosity: resistance to flow–Affects the force with which a particular volcano will erupt
Target #21- I can describe quiet eruptions
• Quiet Eruptions–Form from mafic magma–Low viscosity–Occur with oceanic volcanoes–Magma “oozes” out of the vent
Target #22- I can describe the lava rocks produced from quiet eruptions
• When mafic lava cools rapidly, a crust forms on the surface of the flow
• If the lava continues to flow after the crust forms, the crust wrinkles– Pahoehoe: a volcanic
rock that forms from hot fluid lava• As it cools it forms a
smooth, ropy texture• Means “ropy” in
Hawaiian
Target #22- cont.
• If the crust deforms rapidly, or grows too thick to form wrinkles, the surface breaks into jagged chucks– Aa: a jagged volcanic rock that forms from
lava that• has the same composition as pahoehoe
– Blocky Lava: a volcanic lava that has a high silica content, and is highly viscous
Target #23- I can describe explosive eruptions
• Explosive Eruptions–The felsic lavas of continental volcanoes tend to be cooler and stickier than the fluid lavas produced by oceanic volcanoes• Pyroclastic material: fragments of rock that form during a volcanic eruption
Target #24- I can identify where volcanoes are located
• Volcanoes are usually located at the edge of plate boundaries– Ex: A major zone of
active volcanoes encircles the Pacific Ocean• Known as the Pacific
Ring of fire
– Subduction zones• Continental-oceanic
convergent boundaries• Oceanic-Oceanic
convergent boundaries
Target #24 cont.
• The largest amount of magma is found at divergent boundaries along mid-ocean ridges–The magma erupts to form
underwater volcanoes• These volcanoes produce pillow lava
Target #25- I can differentiate between shield, cinder, and composite
volcanoes• Shield Volcanoes:
volcanic cones that are broad at the base and have gently sloping sides– Covers a wide area– Generally forms from
quiet eruptions– Layers of hot, mafic
lava flow out around the vent, harden, and slowly build up to form the cone
– Ex: Hawaiian Islands
Target #25- cont.
• Cinder Cones: a volcano that has a very steep slope– Not usually tall- max
height is not more than a few hundred meters
– Form from explosive eruptions and are made of pyroclastic material
Target #25- cont.
• Composite Volcanoes: made of alternating layers of hardened lava and pyroclastic material– Quiet eruptions deposits
lava and an explosive eruption follows depositing ash
– Also known as stratovolcanoes
– Develop to form large volcanic mountains
Target #26- I can describe a caldera
• Caldera: a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink– Calderas may fill with
water to form lakes• Ex: Mount Mazama in
Oregon (known as Crater Lake)
Target #27- I can describe how a hot spot forms an island chain
• Hot Spot: an area of volcanic activity within the interior of a tectonic plate– Magma rises from the
mantle in the middle of a plate, and not at a plate boundary
– The rising magma creates a volcano, producing an island
– As the plate shifts over the magma, a new volcano and new island is formed
– Continues creating a chain of islands• Ex: Hawaiian Islands