Cinder-cone volcanoes have symmetrical, steep slopes.
A cinder cone is a volcano with steep, symmetrical sides. The cone forms during explosive eruptions from a single vent that blow lava into the air. Small chunks of lava gradually build the cone when they fall to the ground as pea- and walnut-size cinders. Dirt, trees and snow sometimes cover older cones. Cinder cones that do not appear active can erupt without warning, as Mount St. Helens in Washington did in 1980.
Ash
Ash, the smallest size of cinder, looks like snow as it falls. Heavy ash can suffocate anyone caught in it without protective gear. Lesser amounts can make it hard to breathe, and irritate eyes, mouth, nose and lungs.
Lava Bombs
Globs of airborne lava larger than two and 1/2 inches in diameter are called bombs. Bombs can be molten or solid when they hit the ground, depending on how long they were in the air. Boulder-size rock fragments called blocks can also be thrown into the air. Bombs and blocks can injure or kill people.
Gas
High concentrations of carbon dioxide, sulfur dioxide, hydrogen sulfide and other poisonous volcanic gases can injure and kill people. Carbon dioxide is odorless. Sulfur dioxide's odor, similar to burned matches, and hydrogen sulfide's "rotten egg" odor can warn hikers to leave the area.
Lava Flows
Lava can flow over the rim of a cone's crater or burst out of a cone's base. Some lava moves slower than people walk. Other lava flows move up to 100 mph.
Mudflows
Deadly mudflows can race down a cone's slot when hot volcanic ash, lava and rock mix with snow or water. Volcanic mudflows have buried entire towns.
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