Chapter 15 Lesson 1: Volcanoes – p544-552 – page 1

Vocabulary

Volcano (545) – a vent in Earth’s crust through which melted – or molten – rock flows

Magma (545) – Molten rock below Earth’s crust

Lava (546) – Molten rock that erupts onto Earth’s surface

Hot spot (546) – Volcanoes that are not associated with plate boundaries

Shield volcano (548) – common along divergent plate boundaries and ocean hot spots, these volcanoes are large with gentle slopes of basaltic lavas

Composite Volcano (548) – large, steep-sided volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries

Cinder Cone (548) – small, steep-sided volcanoes that erupt gas-rich, basaltic lava

Volcanic Ash (549) – tiny particles of pulverized volcanic rock and glass

Viscosity (549) – a liquid’s resistance to flow Famous Volcanoes

Do you know the three famous volcanoes that have erupted within the last _______________ years?

o Mount St. Helens (WA, USA) o Kilauea (HI, USA) o Mount Pinatubo (Philippines)

What is a volcano?

A volcano is a _________________ in Earth’s crust through which melted – or molten – rock flows.

Molten rock ______________________ Earth’s surface is called magma.

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How do volcanoes form?

Volcanic eruptions constantly shape _____________________________ o They can form large mountains, create new____________________, and leave a path of

destruction behind

They are created and continue to erupt due to ______________________ plate movement o Volcanoes form at:

___________________ plate boundaries _________________ plate boundaries Hotspots

Convergent Boundaries

Volcanoes form along convergent plate boundaries. o When two plates collide the denser plate sinks, or_________________________, into the mantle. o The ________________________ energy below the surface and fluids driven off the subducting

plate melt the mantle and form magma o Magma is less ________________________ than the surrounding mantle and rises through cracks

in the crust forming a volcano o Lava is molten rock that erupts onto Earth’s _______________________

Divergent Boundaries

Volcanoes can happen here too o Recall that two plates spread ______________________ at divergent plate boundaries. o As the plates_______________________ , magma rises through the vent or opening in Earth’s

crust that forms between them o This process commonly occurs at mid-ocean ridges and forms new _______________________ o More than _____________% of all volcanic activity occurs along mid-ocean ridges

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Hot Spots

Not all volcanoes form on or near plate boundaries o Volcanoes in the _____________________ Island – Emperor Seamount chain are

far from plate boundaries.

Volcanoes that are not associated with plate boundaries are called_______________________.

o Geologist hypothesize that hot spots originate above a rising ________________________ current deep within Earth’s mantle.

They use the word plume to describe these rising currents of hot _______________ material.

o When the plate moves over the plume, a new ________________________ forms

o When the plate moves away from the plume the volcano becomes________________________ , or inactive

Over time, a ______________________ of volcanoes forms as the plate moves. o The oldest volcano will be ______________________________ away from the hot spot.

Where do volcanoes form?

Ring of _________________________

The Ring of Fire represents an area of earthquake and volcanic activity that surrounds the ___________________Ocean.

Volcanoes form mostly along convergent plate boundaries (where plates collide), divergent plate boundaries (where they separate), and over hot spots (like Hawaii)

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Volcanoes in the States

There are _______________ potentially active volcanoes in the United States o Most of these are part of the ring of fire

In the United States, the United States Geologic Society (USGS) has established three volcano _______________________to monitor the potential for future volcanic eruptions

Because of the populated areas surrounding some potentially active volcanoes the USGS has developed a ________________________ assessment program.

o Scientists monitor earthquake activity, changes in shape, ___________________ emissions, and past eruptive history to evaluate the _______________________of future eruptions

Types of Volcanoes

Volcanoes are classified based on their ___________________and____________________. o Magma composition and eruptive style of the volcano contribute to the shape

Shield Volcanoes

Shield volcanoes are common along _____________________ plate boundaries and oceanic hot spots

They are large with _______________________ slopes of basaltic lavas

Composite volcanoes

Composite Volcanoes are large, ______________________-sides volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries

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Cinder Cones

______________________, steep-sided volcanoes that erupt gas-rich, basaltic lavas

Supervolcanoes

Some volcanoes are classifies as supervolcanoes – volcanoes that have large and explosive eruptions

Approximately 630,000 years ago, the Yellowstone ________________________ in Wyoming, USA ejected more than 1000km3 of rhyoltic ash and rock in one eruption

o This eruption produced nearly ________________________ times the volume of material erupted from Mt. St. Helens in 1980.

Volcanic Eruptions

When magma comes to the surface, it might erupt as lava slowly ____________________________ out.

Other times, magma might erupt explosively, sending ______________________ ash – tiny particles of pulverized volcanic rock and glass – high into the atmosphere

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Eruption Style

Magma _________________________________________ determines a volcano’s eruptive style.

The explosive behavior of a volcano is affected by the amount of ___________________ gases, specifically the amount of ______________ ________________, a magma contains

It is also affected by the____________________, SiO2, content of the magma Magma Chemistry

Silica is the main chemical compound in all_______________________.

Differences in the amount of silica affect magma thickness and its viscosity – a liquid’s ______________________to flow

o High silica = ____________________ viscosity Flows like sticky ___________________________________ This type is magma is formed from melt rocks rich in silica or from the mixture of magma

from the mantle and continental crust Volcanic andesite and rhyolite rocks form when intermediate and high silica magma erupt

from subduction zone volcanoes and continental hot spots

Low silica = __________________vviscosity o Flows like warm maple ____________________________ o When the magma erupts, it flows as fluid lava that cools, crystallizes, and forms volcanic basalt. o Erupts along ___________________ _____________________ridges and hot spots

Dissolved Gases

The presence of dissolved gases in magma contributed to how ________________________________a volcano can be

o Like shaking a bottle of soda, the CO2 in the liquid creates the bubbles. When the bottle is opened _______________________________decreases rapidly. The trapped bubbles increase in size and escape the liquid

All magma contains dissolved gas including water vapor and small amounts of CO2 and sulfur dioxide.

As magma moves towards the surface, the pressure from the weight of the rock above_____________________________.

As pressure decreases the gases can no longer remain dissolved and __________________________ begin to form.

Because gases cannot easily escape from high-________________________ lavas, this results in explosive eruptions

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Effects of Volcanic Eruptions

On average, about _______________ different volcanoes erupt each year. o http://www.theatlantic.com/infocus/2013/12/2013-the-year-in-volcanic-activity/100645/

Volcanoes enrich rock and soil with valuable ________________________ and help to regulate climate

Unfortunately, they also can be destructive and sometimes even deadly

o Mount Etna is one of the world’s most active volcanoes. People that live near the volcano are

accustomed to frequent eruptions of both lava and ash. Lava Flows

Because lava flows are relatively _________________ moving, they are rarely deadly

However they can be extremely damaging

Mount Etna in Sicily, Italy, is Europe’s most active volcano. o In May 2008, the volcano began spewing lava and ash in an eruption lasting over ________ months

Although lava is slow moving it threatens nearby __________________________________ o People that live on the slopes of Mt. Etna are use to frequent evacuations

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Ash Fall

During an explosive eruption, volcanoes can erupt large volumes of volcanic __________________ o Ash columns can reach heights of more than _____________km o The ash is a mixture of pulverized rock and ________________

Ash can disrupt traffic and cause airplane engines to stop mid-flight as the ash fuses onto hot engine blades

Ash can also affect air quality and cause serious ___________________________ problems

Large quantities of ash in the atmosphere can also affect __________________by blocking out sunlight and ___________________________ the atmosphere

Pyroclastic Flow

Explosive volcanoes can produce ______________________-moving avalanches of hot gas, ash, and rock called pyroclastic flows.

o “pyro” =______________; “______________” = volcanic particles

Pyroclastic flows travel at speeds of more than 100 km/hr and with temperatures greater than ________°C.

In 1980, Mount St. Helens produced a pyroclastic flow that killed 58 people and destroyed 1 billion km³ of forest.

Predicting Volcanic Eruptions

Unlike earthquakes, volcanic eruptions can be_____________________________.

Moving magma can cause ground_____________________, a change in shape of the volcano, and a series of ____________________ called an earthquake swarm.

Volcanic emissions (release of gases) can increase.

Ground and surface water near the volcano can become more _____________________

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Additionally, geologists will study satellite and aerial photographs, to assess volcanic ________________

Volcanic Eruptions and Climate Change

Volcanic eruptions affect climate when volcanic ash in the atmosphere blocks ____________________

High-altitude wind can move ash around the world.

In addition, sulfur dioxide gases released from a volcano form ______________________ acid droplets in the upper atmosphere

These droplets ______________________sunlight into space, resulting in _______________temperatures as less sunlight reaches Earth’s surface