2 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 pressureMagma: liquid rock produced under Earth’s surface
3 Melting Point: the temperature at which a substance will change from a solid to a liquid Magma can form in three waysTemperature rises above the melting point of rockPressure decreases lowering the melting point of rockAddition of fluids, like water, can decrease the melting pointTarget 16- cont.
4 Target 17- I can define volcanism Target #18- I can differentiate between magma and lava Volcanism: any activity that includes the movement of magma and gases toward or onto Earth’s surfaceMagma rises because it is less dense than the surrounding rockmagma that flows onto Earth’s surface is called lavaFlows from an opening, or vent
5 Target #19- I can differentiate between mafic and felsic magma When magma erupts from a volcano and then cools & hardens, it forms an igneous rockMafic: magma that is rich in magnesium and ironDark in colorMakes up oceanic and continental crustFelsic: magma that is rich in feldspar and silicaLight in colorMakes up continental crust only
6 Target #20- I can describe viscosity Viscosity: resistance to flowAffects the force with which a particular volcano will eruptTarget #20- I can describe viscosity
7 Target #21- I can describe quiet eruptions Form from mafic magmaLow viscosityOccur with oceanic volcanoesMagma “oozes” out of the vent
8 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 wrinklesPahoehoe: a volcanic rock that forms from hot fluid lavaAs it cools it forms a smooth, ropy textureMeans “ropy” in HawaiianTarget #22- I can describe the lava rocks produced from quiet eruptions
9 Target #22- cont.If the crust deforms rapidly, or grows too thick to form wrinkles, the surface breaks into jagged chucksAa: a jagged volcanic rock that forms from lava thathas the same composition as pahoehoeBlocky Lava: a volcanic lava that has a high silica content, and is highly viscous
10 Target #23- I can describe explosive eruptions The felsic lavas of continental volcanoes tend to be cooler and stickier than the fluid lavas produced by oceanic volcanoesPyroclastic material: fragments of rock that form during a volcanic eruption
11 BellworkWhat are the differences between an explosive eruption and a quiet eruption?
13 Target #24- I can identify where volcanoes are located Volcanoes are usually located at the edge of plate boundariesEx: A major zone of active volcanoes encircles the Pacific OceanKnown as the Pacific Ring of fireSubduction zonesContinental-oceanic convergent boundariesOceanic-Oceanic convergent boundariesTarget #24- I can identify where volcanoes are located
14 Target #24 cont.The largest amount of magma is found at divergent boundaries along mid-ocean ridgesThe magma erupts to form underwater volcanoesThese volcanoes produce pillow lava
15 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 sidesCovers a wide areaGenerally forms from quiet eruptionsLayers of hot, mafic lava flow out around the vent, harden, and slowly build up to form the coneEx: Hawaiian Islands
16 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 metersForm from explosive eruptions and are made of pyroclastic material
17 Composite Volcanoes: made of alternating layers of hardened lava and pyroclastic material Quiet eruptions deposits lava and an explosive eruption follows depositing ashAlso known as stratovolcanoesDevelop to form large volcanic mountainsTarget #25- cont.
18 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 sinkCalderas may fill with water to form lakesEx: Mount Mazama in Oregon (known as Crater Lake)Target #26- I can describe a caldera
19 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 plateMagma rises from the mantle in the middle of a plate, and not at a plate boundaryThe rising magma creates a volcano, producing an islandAs the plate shifts over the magma, a new volcano and new island is formedContinues creating a chain of islandsEx: Hawaiian IslandsTarget #27- I can describe how a hot spot forms an island chain