Weekly Online Lesson Online Lesson Archive Grade Level: 8-12 Subject: Geology (Volcanology)

Volcano Hazards

Two weeks ago a small volcanic eruption near the African town of Goma turned into a disaster as two lava flows combined to create a 160-foot-wide path of molten rock moving down the side of Mount Nyiragongo. The lava flow passed directly through the town's main street burning everything in its path and occasionally setting off deadly explosions.

Half a million people were forced to flee Goma into neighboring Rwanda, living in the streets and sheltering at night under shop porches. 180,000 more people remained stranded by the lava on the other side of the city without drinking water or electricity. The U.N. expects food to be delivered to 55,000 households by the middle of next week

The Nyiragongo volcano is one of eight volcanoes on the borders of Rwanda, the Democratic Republic of Congo and Uganda, a region dense with tropical forests and home to rare mountain gorillas. Only two of the volcanoes remain active: Nyamuragira, which erupted early last year, and Nyiragongo.

In this week's online lesson you will learn about volcanoes and lava flows.

USGS Volcano Hazards Program

Perhaps the most authoritative volcano site on the web is the United States Geological Survey, Volcano Hazards program. Watching and
monitoring volcanic activity must certainly be exciting, but even from a great distance volcanoes can be extremely hazardous. Learn more by clicking Types & Effects on the left, and read the introduction. Why is it more important than ever for scientists to provide early and reliable warnings of eruptions?

Below the volcano graphic (and along the top of the page) you will see a list of volcano hazards. Click each link and answer the questions that follow.

Gas. What are the two most abundant gasses released from volcanic systems? Which gasses pose the greatest potential hazard to people, animals and property? What is vog?

Lahars. Where does the word Lahar originate, and what does it mean? What are some other terms used by scientists to describe the properties of lahars? Why do lahars almost always occur on or near stratovolcanoes?

Landslides. Are volcano landslides wet or dry mixtures of debris? How fast can volcano landslides move? Name two reasons why landslides are common on volcanoes.

Lava Flows. What is lava? What three factors determine the speed of a lava flow? What happens when if lava erupts beneath a glacier? What happens if lava enters a body of water?

Pyroclastic Flows. What are pyroclastic flows, and how fast can they move? What are the two parts of most pyroclastic flows? How hot can these flows get? Be sure to watch the Quicktime video that shows how pyroclastic flows are generated. Also, click Pyroclastic surge 18 May 1980 at the bottom of the page to get a sense of the forces involved.

Tephra. Name several examples of tephra. How far downwind of the volcano can these fragments travel? In what ways can volcanic ash damage vehicles and property?

Photo Glossary

While you are browsing around the USGS Volcano site, check out the Photo glossary link under Resources. If you come across a term you don't know, or if you just want to study volcano terms, click the link in the alphabetic photo glossary. You will see an photo of the term along with a brief description. Try these words: obsidian, Pele's hair, and spatter. What do these have in common?

Viewing Lava Safely

People are awed by the natural power and wonder of volcanic and geothermal activity; it's no wonder places like Mount St Helens, Yellowstone National Park, and especially active volcanoes like Kilauea in Hawaii draw tourists from around the world.

You don't have to be a volcano expert to safely view volcanic activity, but you need more than just common sense. Open the USGS fact sheet called Viewing Lava Safely and read the entire page. The fact sheet includes some great images of Kilauea lava flows as well as informative graphics and information. What is a "bench" and why is it unstable? What is a tephra jet and what causes it? What is a whiteout? What are skylights, and why should you stay well away from them?

For Educators

Science educators teaching a unit on volcanoes should browse through the Volcano Resources for Educators section of the site. Along with a list of recommended books and classroom videos to order, you will find online versions of seven volcano pamphlets  from the USGS. All of these would make excellent additions to your online or offline classroom reference library. For offline use, open them and print right from the web (a student aid can do this).

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