Answered by Doug Owen, Park Geologist, Craters of the Moon National Monument. Originally answered March 2012.
Craters of the Moon is a dormant rather than an extinct volcanic area. The volcanoes here are not dead, only sleeping. Indications of impending eruptions — earthquakes, the opening of steam vents, and ground swelling — have not occurred recently. However, geologists believe that the area will become active within the next 1,000 years.
Cinder Cones (excerpted from http://www.nps.gov/crmo)
When magma emerges at the surface along a segment of a rift, it often begins by producing a curtain of fire and a line of low eruptions. As portions of the segment become clogged, the fountains jet higher. If magma emerges at the surface highly charged with gas it sprays high in the air; the fire fountains that produced many of the Craters of the Moon cinder cones were probably over 1,000 feet high. Big Cinder Butte, the tallest cinder cone at Craters of the Moon, is over 700 feet high. The highly gas-charged molten rock cools and solidifies during flight and rains down to form cinder cones. If you look closely at cinders you will see that they are laced with gas holes and resemble a sponge. The erupting cinders form a small cone shape of rocks around the vent. If the eruption continues the cone will continue to grow.
This experiment examines the slope of cinder cones after an eruption. Cinder cones of popcorn, sand and pebbles will be created to see how their slopes compare.
Materials: popcorn, sand, small pebbles,construction paper, paper fastener, paper and pencil
- Cut two strips of construction paper 1″ x 6″ long.
- Fasten the two pieces together at one end of the pieces of paper with the paper fastener. The paper strips should be able to move apart and together to form an angle.
- Taking three cups of popcorn begin dropping the popcorn onto a table or some other flat surface.
- When you have dropped all the popcorn and it has formed a small cone measure the angle of the popcorn cone and record the angle on your sheet of paper.
- Repeat the experiment with sand, check the angle and record the information on your sheet of paper.
- Repeat the experiment with small pebbles.
- How does the size and mass of the cinders affect the slope of the cinder cone?