Igneous Rocks Section 6.2

Rocks Overview A rock is a group of one or more minerals that have been bound together. Three Major Types: Igneous rock formed by the cooling and hardening of magma or lava 2. Sedimentary rock formed by the compactions and cementations of sediment 3. Metamorphic rock formed by the effects of heat and pressure on other rocks

Rocks Overview The rock cycle is the repeated series of events by which rock gradually and continually change from one type to another.

Igneous Rock Formation: The Starting Material Igneous rocks formed from underground magma are called intrusive igneous rocks. When formed at the Earth’s surface, they are called extrusive igneous rocks. Felsic Magma thick, slow moving magma contains large amounts of silica rocks are usually light in color Mafic Magma hotter, thinner magma contains much smaller amounts of silica rocks are usually dark in color

Igneous Rock Formation: Underground Magma Igneous rocks are formed by the cooling and hardening of hot molten rock from inside the Earth. The rate at which magma cools determines the size of the crystals that make up that particular rock. Slow cooling crystals = large crystals Fast cooling crystals = small crystals

Igneous Rock Descriptions Igneous rocks are classified based on the mineral composition and texture. Three main families of igneous rocks: 1. Granite family Felsic rocks Usually coarse grained texture Usually light in color 2. Gabbro family Mafic rocks Dark in color more dense than the granite Family 3. Diorite family Have characteristics of both felsic and mafic rocks Darker than the granite family, but not as dark as the gabbro family. Rocks can be either coarse or fine grained.

Igneous Intrusions An igneous intrusion is a rock mass that forms when magma cools inside Earth’s interior (may be called a pluton). Laccolith Volcanic neck Volcano Sill Dike Batholith

Section 9.1 How and Where Volcanoes Form

Volcano Characteristics A volcano is a landform that develops around the opening in Earth’s crust through which molten rock, ash, and gasses can erupt.

Magma Formation Three ways to form magma: 1. Decrease in pressure 2. Increase in temperature 3. Increase in amount of water in the asthenosphere

Volcanic Activity at Different Boundaries Observe an animation of volcanism at a subduction zone. Ex: The Cascade Range Observe an animation of volcanism along a rift zone. Ex: Iceland Observe an animation of volcanic islands forming over a hot spot. Ex: Hawaii

Where is the volcano being formed?

Section 9.2 Erupted materials

Types of Magma Ways that magma can differ: Silica content Gas content principal ingredient in all magmas Gas content mainly water vapor and CO2 dissolved in magmas at depths where they form Viscosity resistance of a liquid to flow Melting temperature

Explosive Eruption Conditions Magmas high in silica content resist flow Higher gas concentration Lower melting point Location

Flows on Earth’s Surface Lava = hot molten rock that flows out on Earth’s surface Pahoehoe Basaltic lava high in temperature, smooth, rope-like lava that flows very easily

Lava flows on land AA basaltic lava moves slowly and cools quickly into rough jagged rock

Underwater Lava Flows Pillow lava rounded lumps of lava that form underwater crack and form pillow shapes because of the drastic temperature change in the ocean http://player.discoveryeducation.com/index.cfm?guidAssetId=54BFD59D-FB25-435B-B5DF-926F5CBA7E9F&blnFromSearch=1&productcode=US#

Ash and Rock Fragments Pyroclastic flow dense, superheated eruption of gases and pyroclastic material rapid down hill movement at speeds over 100 kilometers per hour

Ash and Rock Fragments Pyroclastic material gases and solid fragments of solid rock that is ejected from a volcano Ex: ash (smallest), lapilli (intermediate), block (largest)

Volcanic Landforms Section 9.3

Types of Volcanoes Shield volcano Cinder Cone volcano Lava flows out of the earth creating a broad base and gentle slopes Composed of basaltic lava Cinder Cone volcano Forms when lava is thrown into the air from a vent and cools before reaching the ground Fragments of molten rock pile up around the volcanic vent Composite volcano Layers of material accumulate around a vent combination of hardened lava, ash, and/or pyroclastic material erupt

Cinder Cone

Composite Volcano

Other Formations Associated With Volcanic Activity Lahar hot ash mixed with snow and ice to form a fast moving mud flow

Other Formations Associated With Volcanic Activity Caldera Large crater-shaped basin at the top of a volcano Usually caused by a collapse in the magma chamber

Other Formations Associated With Volcanic Activity Lava Plateau Large flat area where lava spills out onto the Earth’s surface.