Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2) . Because
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2) . Because of basalt's low silica content, it has a low viscosity (resistance to flow) . Therefore, basaltic lava can flow quickly and easily move >20 km from a vent. The low viscosity typically allows volcanic gases to escape without generating enormous eruption columns. Basaltic lava fountains and fissure eruptions, however, still form explosive fountains hundreds of meters tall.
