Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity. The volcanic complex includes a geothermal field with sulphurous fumaroles and hot springs. Geysers, fumaroles, and hot springs are found both alongside and in the lake. Hot springs, streams, fumaroles, natural gas seeps and volcanic domes dot the caldera floor landscape. The ignimbrite is noted for its fumaroles, phreatic craters, welded tuff, and flattened fiamme. The volcanoes are considered active, and steaming fumaroles and hydrothermal activity may still be seen. Active fumaroles, or volcanic gas vents, can be seen in the inner crater. Red Crater last erupted ash in 1926 and contains active fumaroles. Kibo still has gas-emitting fumaroles in its crater. Alunite also is found near volcanic fumaroles. The volcanic activity of steaming fumaroles and thermal waters are on most of the islands. The summit has a diameter crater, containing fumaroles and sometimes a crater lake. At most times the volcanic activity is limited to steaming fumaroles and boiling mud. Steam and sulphur fumaroles here are indicative of residual activity. It occurs as a precipitate around volcanic fumaroles and solfataras.