(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.
(singular: bacterium) single-celled organisms found in every ecosystem on Earth.
large depression resulting from the collapse of the center of a volcano.
remains of something broken or destroyed; waste, or garbage.
always changing or in motion.
release of material from an opening in the Earth's crust.
vent from which steam is emitted.
natural hot spring that sometimes erupts with water or steam.
large gorge made by the Colorado River in the U.S. state of Arizona.
intensely hot region deep within the Earth that rises to just underneath the surface. Some hot spots produce volcanoes.
small flow of water flowing naturally from an underground water source heated by hot or molten rock.
molten, or partially melted, rock beneath the Earth's surface.
natural spring filled with hot, bubbling mud.
geyser in Yellowstone National Park in the U.S. state of Wyoming.
to turn to stone.
volcano capable of ejecting more than 1,000 cubic kilometers (240 cubic miles) of material.
an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
Yellowstone National Park
large national park in the U.S. states of Wyoming, Idaho, and Montana.