(CNN) Hawaii's Mauna Loa, the world's largest active volcano, erupted this week for the first time in almost four decades.
When volcanoes erupt, they can have disastrous effects on the environment and the communities that live around them. Sunday night's eruption caused flight cancellations to and from Honolulu and sent lava flowing down the side of the volcano.
In erupting for the first time since 1984, Mauna Loa erupted for the first time in nearly 40 years, joining joined its neighboring volcano, Kilauea, which had been erupting for more than a year. The rare dual-eruption event is expected to attract an influx of visitors eager to see their molten flows, the national park said in a Facebook post.
Here is some of the volcano vocabulary you should know to keep up with the eruptions.
Caldera: A caldera is the large, basin-shaped volcanic depression that forms when a volcano erupts and releases magma stored beneath the surface, causing the overlying rocks to collapse. A caldera is different from a crater, which is a smaller depression formed when a volcano erupts and sends rock exploding outward. Yellowstone National Park is home to a famous caldera, measuring 43 by 28 miles.
Lava: Lava is what scientists call magma that breaks through the Earth's surface -- like during a volcano eruption. Lava moves as a fluid or viscous mass, says the US Geological Survey.
Lava fountains: A lava fountain is just what it sounds like: a jet of lava sprayed into the air "by the rapid formation and expansion of gas bubbles in the molten rock," says the USGS. The fountains can reach more than 500 meters (1,640 feet) high.
Lava flows: Lava flows describe both the moving masses of lava that spew onto the earth's surface during an eruption and the solidified deposit they leave behind once they cool down.
Magma: Magma describes the super-hot, molten rock beneath the surface of the Earth, according to the USGS. Stores of magma lie in magma reservoirs or magma chambers underneath volcanoes.
Pele's hair: This term describes long, thin strands of volcanic glass that form from lava fountains and fast lava flows, the USGS says. The strands are named after Pele, the Hawaiian goddess of fire. Swaths of Pele's hair can remain for years and even decades, according to the service, although the wind will eventually strip them from most surfaces.
Tephra: Tephra is a catch-all term for all the fragments of rock that are ejected into the air by an erupting volcano, the geological survey says.
Volcanic ash: Volcanic ash isn't the same as the ash produced after burning a piece of paper. Volcanic ash, a finer form of tephra, consists of tiny, sharp pieces of rock and glass. It's hard and abrasive and doesn't dissolve in water, according to the USGS. Clouds of volcanic ash pose a danger to air traffic because they reduce visibility, can damage flight controls and can even cause jet engines to fail.
Vog: Vog, a portmanteau of "volcanic" and "smog," describes the "hazy air pollution" produced by volcanic emissions, according to the Interagency Vog Dashboard.
The pollution mostly consists of water vapor, carbon dioxide and sulfur dioxide. Vog can pose environmental and health risks, says the USGS.