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6.1 Objectives: You will learn to describe how volcanoes can affect people. You will learn to list conditions that cause volcanoes to form. You will learn to identify the relationship between volcanoes and Earth’s moving plates.
VOLCANOES
Chapter 6
Volcanoes and Earth’s Moving Plates
What are volcanoes? - openings in Earth’s surface - mountains formed by lava & volcanic ash - most are dormant - Mt. St. Helens is the largest in North America - Kilauea, Hawaii is the most active in the world - more than 600 are active
- may cause lung disease Effects of Eruptions - collapsed buildings - blocked roads - may cause lung disease in people and animals
How do volcanoes form? Heat and pressure causes rock to melt and form magma 2. Magma is less dense than other rock and is forced upward 3. After thousands/millions of years it reaches Earth’s surface and flows out through a vent 4. Steep wall around the vent is the crater
Where do volcanoes occur?
1. Divergent Boundaries where plates move apart - form long deep cracks (rifts) ex. Mid-Atlantic Ridge formed Iceland
2. Convergent Boundaries
ex. Mount St. Helens in the Cascade Range plates move together ex. Pacific Ring Of Fire ex. Mount St. Helens in the Cascade Range
Mt St. Helens
3. Hot Spots area at the boundary between Earth’s mantle and core that is hotter than other areas magma is forced upward towards the crust ex. Hawaiian Islands
Let's Review! gases ash lava lava flows pyroclastic flows falling ash A volcano is an opening in Earth’s surface that erupts ________, ________, and ________. Direct effects of volcanic eruptions, can be caused by ______________, ______________, and ______________. Volcanic eruptions also produce indirect effects, such as ________. Volcanoes form when magma is forced up and flows onto Earth’s surface as ________. A ________ is a steep-walled depression around a volcano’s vent. Volcanoes form when one plate ________ beneath another plate, where two plates are moving ________, and at ________. gases ash lava lava flows pyroclastic flows falling ash acid rain Let's Review! lava crater sinks apart hot spots
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Students will learn to list three forms of volcanoes. 6.2: Types of Volcanoes Objectives: Students will learn to explain how the explosiveness of a volcanic eruption is related to the silica and water vapor content of its magma. Students will learn to list three forms of volcanoes.
Mount St. Helens – sequence of eruptions
What controls eruptions? 1. amount of water vapor and other gases trapped in the magma 2. amount of silica present in the magma
3 Types of Eruptions Exist: 1. Quiet 2. Explosive/Violent 3. Quiet/Explosive
basaltic magma contains less silica and is very fluid 1. Quiet basaltic magma contains less silica and is very fluid example: Kilauea
2. Explosive/Violent granitic magma contains a lot of silica, is very thick, and gets trapped in vents causing pressure has a high water content
Quiet/Explosive - Andesitic magma is more silica rich than basaltic magma, but less silica rich than granitic magma - Because of a higher silica content than basaltic, these volcanoes erupt more violently than basaltic magmas
Forms of Volcanoes
- broad with gently sloping sides Shield Volcano!!! - quiet eruption - basaltic lava - broad with gently sloping sides - ex. Hawaiian Islands
- throws tephra in the air Cinder Cone Volcano!!! explosive - throws tephra in the air - steeps sides
Composite Volcano!!! Sometimes called a Stratovolcano Varies between quiet and violent Tephra and lava layers are repeated over and over
Mt. Fuji, Japan
Mt. Rainier, Washington
Let's Review... water vapor eruption silica silica rich silica poor The amount of _____________ and other gases control the type of __________ and the amount of _______ present in the magma. Magma can be divided into two major types – ___________ and ____________. A ________ volcano is a broad, gently sloping volcano formed by quiet eruptions of basaltic lava. A ____________ volcano is a steep-sided, loosely packed volcano formed from tephra. ___________ volcanoes are formed by alternating explosive and quiet eruptions that produce layers of tephra and lava. eruption silica silica rich silica poor shield cinder cone Composite
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Review: What factors control the type of eruptions that occur? Do Now!!! Review: What factors control the type of eruptions that occur?
You will learn to explain how a volcanic neck and a caldera form. Objectives!!! You will learn to describe intrusive igneous rock features and how they formed. You will learn to explain how a volcanic neck and a caldera form.
6.3: Igneous Rock Features!!! - rock cooled under ground
largest intrusive igneous rock forms when magma cools underground Batholiths largest intrusive igneous rock forms when magma cools underground some have been exposed due to erosion
YOSEMITE STATE PARK
Magma squeezed into vertical cracks Dike Magma squeezed into vertical cracks
Magma squeezed into horizontal cracks Sill Magma squeezed into horizontal cracks
Solid igneous rock in the vent after cone has eroded away Volcanic Neck Solid igneous rock in the vent after cone has eroded away
Devils Tower
Top of volcano collapses Caldera Top of volcano collapses
Crater Lake ( 1,932 ft. deep)
Diameter is 5 miles
Intrusive igneous rock features Let's Review!!! Intrusive igneous rock features _______________________________ are formed from magma that is forced upward toward Earth’s crust, then slowly cools and __________ underground _______ reaching the surface. __________, ______, and _____ are a few examples of intrusive igneous rock features. A ______________ is the solid igneous core of a volcano left behind after the softer cone has been ________. A _______ is a large, circular-shaped ___________ that forms when the top of a volcano collapses. solidifies before Batholiths dikes sills volcanic neck eroded caldera depression
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