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100

tundra

treeless plain where only grasses and mosses grow

100

prairie

flat or rolling land covered with grass

100

canyon

deep valley with very high steep sides`

100

glacier

a large mass of ice

100

economy

the way a country's people use natural resources, money and knowledge to produce goods and services

200

megalopolis

large urban area formed by large cities

200

tributary

river or stream that flows into a larger river

200

wetland

low, flat area covered with water

200

renewable resource

material found in nature that can be replaced, such as forests

200

irrigation

a method of supplying dry land with water through a system of ditches and pipes

300

Continental Divide

Imaginary line made of high points in the Rockies from where our nation's rivers flow east or west.

300

hydroelectric power

electricity made from flowing water in rivers

300

scarcity

shortage of available goods and services

300

current

water or air that flows usually in the same path

300

drought

a long period with little or no rainfall

400

precipitation

moisture that falls to the ground in the form of rain, sleet or snow.

400

arid

dry

400

tornado

a powerful windstorm with a funnel shaped cloud

400

hurricane

cyclonic wind storm with strong winds and rain, over the ocean and on to land.

400

blizzard

heavy snowstorm with strong winds

500

plate tectonics

theory that Earth's surface is made up of plates and is contantly moving

500

global warming

the gradual increase of Earth's temperature

500

levee

an earth wall that farmers build to keep water from overflowing on land

500

water table

underground water that is close to Earth's surface.

500

What was the name of the costliest and deadliest hurricane in the history of the United States and what city was affected most?

Hurricane Katrina/New Orleans