2 Section 18-1 Magma Objectives: Describe factors that can affect the formation of magmaCompare and contrast the different types of magma
3 Volcanic EruptionsIn the last 10,000 years more than 1500 major volcanic eruptions have been recorded…where and why do these eruptions occur?
4 How Magma FormsRecall that magma is a mixture of molten/melted rock, suspended mineral grains, and dissolved gasses found deep beneath the Earth’s surface.
5 How Magma FormsMagma usually forms at temperatures between 800 and 1200 C (1600 to 2400 F)The temperature, and the pressure on the rock along with the amount of water in the rock all determine at what temperature the rock will melt.
11 Basaltic MagmaTypically forms when rocks in the upper mantle begin to melt, it tends to be fast moving and relatively quiet as it erupts due to its low gas content.
12 Andesitic MagmaAndesitic magma is made in subduction zones and is typically about 60% silica, it tends to move and erupt at a medium pace.
13 Rhyolitic MagmaRhyolitic magma is thick and slow moving…it is filled with gas and water and tends to be very explosive because pressure builds within it.
14 ViscosityViscosity refers to the rate or speed at which something will flow.If something has a high viscosity, the thicker and slower it will flowIf something is said to have a low viscosity, the thinner and faster it will flow.
15 Section 18-2 Intrusive Activity Objectives:Explain how magma affects overlying crustal rocksCompare and contrast intrusive igneous rock bodies
16 Density and MovementBecause molten rock is nearly liquid compared to the solid rock around it, it is less dense and wants to move upward.What happens as the magma flows upward into cooler crust? The process is called “intrusion”.
18 IntrusionsThe magma can force the solid rock to push apart and create fissuresThe magma can contact the upper solid rock and cause pieces of it to melt and fall into the magma poolThe magma can immediately melt the rock into which it flows
19 PlutonsAs the flowing magma cools inside of the solid rock, it crystalizes and forms blocks, ribbons or veins of new “intrusive” igneous rock.
20 BatholithsBatholiths are the specific name given largest formations of plutons. They are usually found in large mountain ranges. They cut across rock layers.
21 LaccolithsLaccoliths tend to form near the Earth’s surface where they cause the rock above to push upward in a dome shape.
22 SillsSills are intrusions that form parallel to the existing rock, they tend to stay underground and flow like a “spill”.
24 Plate MovementUnderground plutons can be brought to the surface as tectonic plates converge and push upward exposing the rock within it.Most igneous rock on the surface of the Earth is not from volcanic activity but from the slow gradual process of plate tectonics.
26 Section 18-3 Volcanoes Objectives: Describe the major parts of a volcanoCompare and contrast shield, cinder-cone, and composite volcanoesContrast the volcanism that occurs at plate boundaries
27 Anatomy of a VolcanoThe magma that erupts to the Earth’s surface is then called lava.The lava erupts through an opening in the crust called a vent.The lava will cool and solidify around the vent forming a mountain that is called a volcano.
28 Anatomy of a VolcanoAt the top of a volcano around the vent is a bowl-shaped depression called a crater
29 Types of Volcanoes The appearance of a volcano depends on two factors: The type of material that forms the volcanoThe type of eruptions that occur
33 Cinder-Cone Volcanoes Very steep mountain/volcano that results from material being ejected straight up into the air and falling back down around the ventMagma/lava contains some gases that make the eruptions explosive
35 Composite VolcanoesLarger versions of cinder-cone that have been made of layers of lava and solid material. The magma/lava that makes them up is full of gas that builds up until it finally explodes violently.Mt. St. Helens
37 Volcanic MaterialRock fragments thrown into the air during an eruption are called tephra.Classified by sizeDustAshLapilliVolcanic blocks (angular)Volcanic bombs (rounded)
38 Pyroclastic FlowsViolent eruptions that send out a wave of gas, ash, and tephra that can travel up to 400 mph.
39 Where do Volcanoes Occur? The distribution of volcanoes around the world is not random, most occur at plate boundaries.80% convergent15% divergent5% non-boundary “Hot Spots”
40 Convergent VolcanismPlates coming together, this forms the Pacific Ocean “Ring of Fire” and the “Mediterranean Ring” in the Atlantic.
41 Divergent VolcanismPlates spreading apart also create a way for magma to escape…these are called rift zones.Mid-Atlantic Ridge
42 Hot SpotsThe Hawaiian Islands are not formed along a plate boundary but instead are found in an area of the mantle that is usually hot called a “hot-spot”As the plates move over the hot spot volcanoes form.