Phreatic eruptions occur when confined, sub-surface geothermal waters are heated to temperatures above their boiling point and flash to steam, thereby expanding to form an explosion. Such eruptions eject abundant hot steam, hot water, mud and old rock debris in to the air. In some cases the mud and water ejected may be acidic. No new magma is involved in a phreatic eruption, although the heat needed to flash water to steam and thus generate a phreatic eruption is often provided by an underlying magma body. In some instances, particularly if they occur in a sequence, phreatic eruptions may herald the arrival of an actual magmatic eruption. In the Eastern Caribbean, there have been numerous phreatic eruptions, e.g. the 1976-1977 eruption of La Soufrière in Guadeloupe, the 1880 and 1997 eruptions in the Valley of Desolation in Dominica and the 1766 eruption at Sulphur Springs in Saint Lucia