Bell Ringer The ___________ eon is divided into 3 eras: Paleozoic (“_______”), Mesozoic (“middle life”), and Cenozoic (“__________”) Phanerozoic old life recent life

Volcanoes

Anatomy of a Volcano Volcano – a mountain or hill with a vent through which lava, rocks, and gas erupt from the Earth’s crust Summit – sides of the volcano Vent – opening through which lava erupts

Anatomy of a Volcano Crater – bowl-shaped opening (< 1km wide) around the vent Caldera – large crater formed when the summit collapses during or after an eruption Crater Caldera

Caldera Lake (Oregon)

Anatomy of a Volcano Famous Calderas -- Santorini Caldera in Greece and Yellowstone Volcano in the US

Yellowstone is an example of a dormant (inactive) supervolcano If it ever erupts, it could potentially change all life on Earth

Anatomy of a Volcano Magma chamber – pool of magma below the volcano that fuels the eruption Magma – mixture of molten (hot, melted) rock, suspended minerals, and gases

Magma Magmas are named after the igneous rocks that form from the magma Three types of magma: Basaltic (Mafic) Andesitic Rhyolitic (Felsic) Basaltic Lava

Magma Viscosity – a substance’s internal RESISTANCE to flow

Magma The HIGHER the viscosity, the more a substance resists flowing. This means the substance is thicker, flows slowly, and is more like a milkshake’s consistency The LOWER the viscosity, the less a substance resists flowing. This means the substance is thinner, flows easily, and is more like milk or water’s consistency

What Affects Viscosity? 1. Temperature – the warmer the substance, the lower the viscosity Ex: you can heat up honey to make it flow better Hotter magma has lower viscosity (flows more quickly) than cooler magma As magma cools, it slows down and hardens into volcanic rock

What Affects Viscosity? 2. Silica Content – the higher the silica content in a substance, the higher the viscosity Magma with lots of silica has higher viscosity (flows more slowly) than magma with little silica The higher the silica content, the more explosive the eruption

Type of Magma Silica Content Viscosity Eruption Basaltic (Mafic) Quiet, Not Explosive Andesitic Medium Eruptions Rhyolitic (Felsic) Highly Explosive Low Low Medium Medium High High

Types of Volcanoes Three types of volcanoes (that correspond with the three types of magma) Shield Cinder Cone Composite

Shield Volcanoes Broad, gently sloping sides with a nearly circular base Non-explosive eruptions (lava just flows out the vent with no real “eruption”) Lava has low amounts of silica and low viscosity Example: Hawaiian Islands

Cinder Cone Volcanoes Steep-sided, generally small (< 500m high) More explosive eruptions than shield volcanoes Lava has more silica and higher viscosity than shield volcanoes

Composite Volcanoes Tallest of all volcanoes Highly explosive eruptions, most dangerous to humans

Composite Volcanoes Lava has high amounts of silica and a high viscosity Examples: Mount St. Helens and Mount Rainier, both in Washington State

Summary Volcano Type Appearance Eruption Strength Silica Content Viscosity Shield Broad, sloping sides Cinder Cone Steep sides and small Medium Composite Tallest Not explosive Low Low Highly explosive High High

Based on this information, match the types of magma with the types of volcanoes: Shield Cinder Cone Composite Basaltic/Mafic Andesitic Rhyolitic/Felsic

Questions about the Quiz?

Quiz Put MC answers in blanks. Attempt every question! Turn in when done I will pass out progress reports as you finish IF YOU WANT YOUR MAKEUP WORK: PUT YOUR NAME ON A PIECE OF PAPER, WRITE DOWN THE ASSIGNMENTS YOU ARE MISSING, TURN IT IN; I WILL GIVE THEM TO YOU TOMORROW

Dante’s Peak -- Background Fictional volcano Dante’s Peak hasn’t erupted in over 7,000 years. Two people were swimming in hot springs when the springs began to boil, killing the people. Geologists were called in to investigate.

The head geologist (Harry) is concerned, but doesn’t have any scientific proof that the volcano is going to erupt. The town decides to keep it quiet for two reasons: 1) the volcano hasn’t erupted in 7,000 years and 2) the last threat was a false alarm that really hurt tourism and the town’s economy The geologists are about to leave town when they notice that the tap water is brown and smells like sulfur…

As we’re watching, keep the following questions in mind: Why didn’t the people evacuate? If you had been a resident of that town, would you have evacuated? What real-life disaster have we talked about in class where people did not follow the advice to evacuate? 50:54