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Overview
Students learn about volcanic processes at Cascade volcanoes as they view the graphics provided, research processes further and write results on a student page. As an optional activity, students prepare a booklet or computer presentation about each process with an emphasis on process interaction. This activity is offered as an alternative to the Understanding Volcanic Hazards video that may be unavailable or inappropriate for your students.
Learner Objectives:
Students will: ● (^) Recognize the scope of geologic processes that occur at Cascade volcanoes ● (^) Identify volcanic processes seen in photographs ● (^) Understand that, during an eruption, volcanic processes often occur simultaneously or sequentially.
Setting: Classroom
Timeframe: 40 minutes
Materials:
● (^) Copies of “Volcanic Processes” student page ● (^) Nine graphics illustrating “Common Volcanic Processes at Cascade Volcanoes” (computer projection, transparencies, or paper copies to students) ● (^) Library or Internet access
Grade Level: 3–
Volcanic Processes
Vocabulary: Blocks, bombs, crater, debris
flow, earthquake, eruption, eruption cloud, explosive eruption, fractures, fumarole, hydrothermal alteration, lahar, landslide, lava, lava dome, lava flow, magma, pyroclastic flow, tephra, volcano, volcanic ash, volcanic gas
Skills: application, interpretation,
inference
Benchmarks:
See benchmarks in Introduction.
Activity last modified: November 21, 2014
U.S. Department of the Interior U.S. Geological Survey General Information Product 19
Living with a Volcano in Your Backyard-
An Educator's Guide with Emphasis on Mount Rainier Prepared in collaboration with the National Park Service
NATIONALSERVICEPARK
Teacher Background
Background information about volcanic processes can be found in the teacher pages that follow.
Procedure
Volcanic Processes
The term volcanic processes refers to eruptive and noneruptive activities that take place on volcanoes. Students viewing photos individually may get the faulty impression that volcanic events occur in isolation. During an eruption, volcanic processes often occur simultaneously or sequentially, as explained in the descriptions below. Keep in mind that one of the objectives for this activity is this recognition of volcanic processes occuring in a sequence rather than in isolation.
1. Display the individual graphics, one through nine and for end review, repeat graphic one. Convey the written information to students by paraphrasing, reading, or providing the pages to the students. Alternatively, make copies of each graphic and distribute it to groups, or at stations around the classroom.
2. Distribute the " Volcano Processes " student page. Students should work in small groups to research processes further and write definitions and descriptions beside each graphic.
3. Discuss the information learned in student research. Emphasize the wide range of geologic processes that occur on Cascade volcanoes; identification of volcanic processes seen in photographs; and knowledge that, during an eruption, volcanic processes often occur simultaneously or sequentially.
Adaptations
◆ (^) Older students can perform an Internet or library search for information about these processes. Students then create a volcano book, collage, or computer presentation with text, definitions, and additional graphics.
Extensions
◆ (^) Students conduct Internet research to discover where these processes are observed at volcanic eruptions today. Instruct students to write a report about the progression of volcanic processes noted by observers over the course of an eruption. For a list of eruptions in progress, visit the Web site for Smithsonian Global Volcanism. The address is found at Internet Resources.
Volcanic Processes -continued...
Graphic 1 — Overview
Common sequences of events at stratovolcanoes:
Before an eruption begins, rising magma opens cracks (fractures) in rocks beneath the volcano , commonly causing earthquakes , deformation of the land surface and gas release. During the onset of an explosive eruption , volcanic gases in the magma expand and break magma into tiny pieces called tephra. After many of the gases have dispersed in the atmosphere, a more fluid lava pool within the crater rises and flows over the crater lip as a lava flow. The ensuing lava flows sometimes break apart on steep volcanic terrain as avalanches of hot rock and gases. These pyroclastic flows (sometimes called hot ash flows), melt snow and ice, providing the water for debris flows and lahars (large debris flows). Pyroclastic flows also originate from the collapse of eruption columns-the dark column of ash, steam, and other gases that rises above an explosively erupting volcano. Rocks that have been weakened by hot acidic groundwater ( hydrothermal alteration ) become more susceptible to collapse as a landslide. Volcanoes can also erupt nonexplosively, without tephra. Where lava is too viscous to flow, it forms a dome-shaped feature commonly called a lava dome.
Graphic 2 — Tephra — Volcanic ash fall from
Mount St. Helens darkens Yakima,
Washington, at noon on May 18, 1980
Explosive eruptions blast fragments of rock high into the air. Large fragments fall to the ground near to the volcano, while small fragments create large eruption clouds capable of traveling thousands of kilometers (miles) from the volcano. Volcanic ash clouds are usually nontoxic but have the capability to disrupt peoples' lives for long periods. Heavy ash fall can collapse buildings, and even minor ash fall reduces visibility and can damage crops, electronics, and machinery. Aircraft that fly into a volcanic ash cloud are at great risk of engine failure.
C o m m o n Vo l c a n i c Pro c e s s e s a t
C a s c a d e Vo l c a n o e s
Graphic 3 — Tephra — Volcanic blocks and bombs at
Kilauea Volcano, Hawaii
A volcanic block is a solid rock fragment greater than 64 millimeters (2.5 inches) in diameter that was ejected from a volcano during an explosive eruption. Blocks commonly consist of solidified pieces of old lava flows that were part of a volcano’s cone.
By comparison, semi-solid rock can be aerodynamically shaped into a variety of forms called volcanic bombs.
Graphic 4 — Lava flow on Villarica
Volcano in Chile
Lava is molten rock that pours or oozes onto the planet surface. Lava flows cool and harden faster on the outside (within minutes), than on the inside, where cooling continues for days to years.
Graphic 5 — Pyroclastic flow on
Montserrat Volcano in the Caribb ean
Pyroclastic flows are avalanches of hot lava fragments and volcanic gases formed by the collapse of ash clouds and lava domes and flows. These flows rush down the mountain at speeds up to a few hundred kilometers (miles) per hour. They destroy everything in their path by impact, incineration, asphyxiation, or burial. Nothing will survive in the path of a pyroclastic flow.
C o m m o n Vo l c a n i c Pro c e s s e s
a t C a s c a d e Vo l c a n o e s (^) - c o n t i n u e d
Graphic 7 — Debris flow in Tren, Canton of
Grissons, Switzerland
At Mount Rainier, small flows of water, mud and rock debris that stay within park boundaries are know locally as debris flows. Flows that travel beyond park boundaries are classified as lahars. Debris flows commonly occur during noneruptive times, especially during periods of intense rainfall or snowmelt, as opposed to lahars, which are generally caused by eruption or landslide activity.
Graphic 8 — Landslide at Casita Volcano
in Nicaragua
A landslide, or debris avalanche, is a rapid downhill movement of rock and overlying material. Volcano landslides can be small movements of loose debris on the surface of a volcano or massive collapses of the entire summit or sides of a volcano. Steep-sided volcanoes can be especially vulnerable to landslides, since they are built partially of layers of loose volcanic rock fragments, which break free and move downhill. Landslides on volcano slopes are triggered when eruptions, heavy rainfall, or large earthquakes occur.
Graphic 9 — Hydrothermal Alteration
Weakens Lava Rock at Mount Rainier,
Washington
Some rocks on volcanoes have been altered to soft, slippery clay minerals because of exposure to circulating hot, acidic ground water, a process called hydrothermal alteration. Entire portions of a volcano can be left susceptible to collapse through landslides. Altered rock is often visible in the vicinity of fumaroles, or steam vents on the volcano’s surface.
C o m m o n Vo l c a n i c Pro c e s s e s a t
C a s c a d e Vo l c a n o e s (^) - c o n t i n u e d
Instructions: Learn more about each of the volcanic processes listed below. Write definitions
and descriptions beside each graphic.
Tephra
Volcanic Processes Definitions and Descriptions
Pyroclastic Flow
Landslide
Lahar or debris flow
Lava Flow
Vo l c a n i c Pro c e s s e s
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Photo by Jack Whitnall
Volcanic Processes
—
Graphic 2
—
Tephra
—
Volcanic ash fall from Mount
St. Helens darkens Yakima, Washington, at noon on May 18, 1980
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Photo by Christina Heliker, USGS
Volcanic Processes — Graphic 3 — Tephra —
Volcanic blocks and bombs at Kilauea Volcano, Hawaii
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Volcanic Processes
—
Graphic 5
—
Pyroclastic flow on Montserrat
Volcano in the Caribbean
Photo by Willie Scott, USGS
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Volcanic Processes
—
Graphic 6
—
Lahar at Armero, Colombia
Photo by Richard Janda in 1985, USGS
Living with a Volcano in Your Backyard–An Educator's Guide: U. S. Geological Survey GIP 19
Volcanic Processes
—
Graphic 8
—
Landslide
at Casita Volcano in Nicaragua
Photo by Kevin Scott, USGS
Photo by Steve Brantley, USGS
Volcanic Processes
—
Graphic 9
—
Hydrothermal Alteration
Weakens Lava Rock at Mount Rainier, Washington
