An extensive volcano glossary can be found at volcanoes.usgs.gov. Above left: Mt. St. Helens, a grande dame among andesitic volcanoes, erupts on July 22, 1980.

The type of lava erupted by Nyiragongo and many volcanoes in the East Rift zone ... a large elongated fissure or fracture (as seen on the diagram above) or a tiny ground crack.