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Mystery of the Megaflood

Classroom Activity


Activity Summary
Students will use everyday items and speeds to describe the dimensions of a massive flood that occurred in the Pacific Northwest near the end of the last ice age.

Learning Objectives
Students will be able to:

  • demonstrate how well-known items can serve as tools for nonstandard measurement.

  • calculate length, width, height, and speed of different features related to the Spokane Flood.

Materials for teacher
  • meter stick
  • yardstick

Materials for each team
  • copy of the "How Big Is That?" student handout (PDF or HTML)
  • copy of the "The Spokane Flood" student handout (PDF or HTML)
  • copy of the "Comparison Items List" student handout (PDF or HTML)
  • calculator
  • access to print and Internet resources

A glacier is a large mass of perennial ice that is formed when snowflakes pack down and recrystallize as solid ice. Although ice appears as a hard solid, glaciers flow slowly downslope under their own weight. Like a river, a glacier picks up and carries rock particles of all sizes. As the glacier moves, the particles are deposited and accumulated in mounds called moraines. In addition, glaciers can shrink and grow in response to climate changes. These changes occur over tens, hundreds, and even thousands of years.

Glaciers exist on all seven continents. About 10 percent of the world's land is covered with glaciers, most of which are found near the poles. One type of glacier is found only in polar regions of the world or at high altitudes. Called polar glaciers, these types of glaciers most often create icebergs, which are formed when a piece of glacier breaks off to float in the sea. Most U.S. glaciers are found in Alaska. The Bering Glacier in Alaska qualifies as North America's longest glacier, measuring 204 kilometers long.


Part I

  1. Large dimensions can be difficult to grasp. Often large dimensions are more comprehensible when likened to well-known objects. Students in this activity will develop ways to represent the dimensions associated with a massive flood event that took place sometime between 16,000 and 12,000 years ago in what is now Washington State.

  2. The measurements in this activity are represented in meters. To help students understand the difference between standard and International System of Units (SI) measurements, hold up the meter stick and yardstick together. How do they differ in length? How many meter sticks would reach the ceiling? How many yardsticks? (Teachers who would like to do the activity in standard units can have students convert the measurements to standard prior to doing the activity.)

  3. Next, ask students which distances are easier to imagine:

    • 275 meters or almost three football fields?
    • 4,725 kilometers or the distance between New York and San Francisco?

    Most students would choose the second measurement in both examples because those dimensions are more easily visualized than the large numerical measurement.

  4. Organize the class into teams and provide each team with copies of the student handouts. Review with students the activity instructions listed on the "How Big Is That?" handout. Discuss with students why it can be helpful to use nonstandard forms of measurement to describe something. (It may be easier to communicate the meaning of a standard measurement through comparison with commonly known objects.) When should nonstandard forms of measurement be used? (Nonstandard forms of measurement can be useful when communicating large measurements to a non-scientific audience.) When are nonstandard forms of measurement less useful? (Nonstandard forms of measurement are generally estimates and do not provide the mathematical accuracy that science often requires.)

  5. First have students categorize the Comparison Items List into the following five categories: length, height/depth, area, volume, and speed. Then have students read "The Spokane Flood" description and highlight each of the measurements within it. Divide up the measurements in the reading among teams (see Activity Answer for a list of measurements that appear in the story). Make sure that the same set of measurements is assigned to more than one team.

  6. Have each team choose items from the Comparison Items List to represent the team's assigned measurements. Have teams perform the calculations necessary to create new representations of the measurement in the reading into items they have chosen from the Comparison Items List.

  7. Help students with calculations as necessary. Converting length, height/depth, and speed are simple proportions—so many of these equal so many of those. Students may need assistance converting area and volume, however. For example, although there are 3 feet in a yard, there are 9 cubic feet in a cubic yard (3 feet * 3 feet * 3 feet = 9 feet3). Students may benefit from a brief refresher about finding area and volume:

    a = l • w
    v = l • w • h
  8. After each team uses the items from the Comparison Items List to create a new representation of its assigned measurements, have teams that have done the same measurements from the reading pair off to check their results and discuss their choices.

  9. Ask all teams to report their equivalent measurements. Discuss and work out any discrepancies in differing results.

Part II

  1. Hold a class discussion about other comparison items that might be good to use to bring meaning to the large flood measurements. Record these on the board. Assign teams items from the newly created class comparison items list.

  2. Have teams use print and Internet resources to find the measurements for the new comparison items they have been assigned. Then have students convert their original assigned measurements from the reading to the new comparison items they have researched.

  3. When all teams have finished, have each team report its representations using the new comparison items list created by the class. Record unusual or controversial representations on the board. Once all teams have reported, have a class discussion about the results. Which ones are most comprehensible? Why? What are some common features of good analogies?

  4. As an extension, have students research the measurements of the seven wonders of the ancient world and develop ways to represent them in more comprehensible terms.

Activity Answer

Analogies can be useful to give meaning to large quantities. How Much Is a Million?, by David M. Schwartz, is a children's book that explores this technique. "A billion kids would make a tower that would stand up past the Moon," is one example from the book. Here are how some of the items from the Comparison Items List relate to the dimensions in the flood story.

Flood Dimension

New Representation

Comparison Item


height: 762 m

twice as high as

the Empire State Building (381 m)

Lake Missoula

depth: 610 m

almost twice as deep as the height of

the Eiffel Tower (321 m)

area: 7,770 sq km

slightly larger than the area of

Delaware (6,447 sq km)

volume: 2,084 cu km

more than four times larger than

Lake Erie (483 cu km)


length traveled: 842 km

more than twice the distance from

New York City to Washington D.C. (386 km)

area covered: 41,440 sq km

almost half the area of

Maine (91,700 sq km)

height at tallest: 244 m

almost one and a half times the height of

the Washington Monument (170 m)

maximum flow rate: 40 cu km/hr

more than 350 times the flow rate of

the 1993 Mississippi River flood, peak flow rate (0.11 cu km/hr)

Grand Coulee Canyon

length: 80 km

almost twice the distance of

a standard marathon race (42.2 km)

width: 10 km

almost four times the length of

San Francisco's Golden Gate Bridge (2.7 km)

height: 274 m

more than one and a half times as high as

the Washington Monument (170 m)

Dry Falls

height: 107 m

a stack of about 11

two-story houses (each 10 m)

width: 4.8 km

about six times wider than

Niagara Falls (Horseshoe Falls only) (792 m)

Camas Prarie Hills

height: 11 m

as high as

a common utility pole (11 m)

width between hills: up to 152 m

wider than six lengthwise

tennis courts (23.8 m)

area: 16 sq km

about half the size of

Chicago's O'Hare Airport (28.3 sq km)

flood velocity through: 85 km/hr

almost two and a half times faster than

a world-class sprinter (36.9 km/hr)

Wallula Gap

daily amount through: 167 cu km

almost 65 times more than the

1993 Mississippi Flood, peak flow rate (0.11 cu km/hr)

Links and Books

Web Sites

NOVA—Mystery of the Megaflood
Read what one geologist has to say about megafloods, discover what Glacial Lake Missoula was like before it burst, use an interactive map to explore the scablands, and test your hunches about the earthly forces that made eight super structures.

A Brief Introduction to the Ice Age Floods
Provides information on how the Pacific Northwest ice floods occurred and how scientists came to understand what happened, as well as links to additional resources.


The Channeled Scablands of Eastern Washington
by Paul L. Weis and William L. Newman. Eastern Washington Press, 1989.
Looks at J Harlen Bretz's theory that the scablands were formed by a giant flood, and Bretz's eventual vindication after years of disbelief by fellow geologists.

Glacial Lake Missoula and Its Humongous Floods
by David D. Alt. Mountain Press, 2001.
Describes Glacial Lake Missoula and traces the periodic floods' routes across northern Idaho, the Columbia Plateau, and down the Columbia River to the Pacific Ocean.


The "How Big Is That?" activity aligns with the following Principles and Standards for School Mathematics (see

Grades 3-5
Mathematics Standard


Grades 6-8
Mathematics Standard


Classroom Activity Author

Developed by James Sammons and WGBH Educational Outreach staff. Sammons has taught middle and high school science for 30 years. His teaching practices have been recognized by the National Science Teachers Association, the Soil Conservation Service, and the National Association of Geoscience Teachers.

Teacher's Guide
Mystery of the Megaflood

Video is not required for this activity
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