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.
Grade 8 Integrated Science Chapter 15 Lesson 2 on volcanoes. This lesson goes into detail about volcanoes, plate boundaries, lava chemistry, eruption types, and volcano types. The purpose of this lesson is for students to understand where and why volcanoes form and what factors cause differing volcanic features. *Thi
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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
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
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)
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
______________________, 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
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
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
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 _____________________