The Hawaiian volcanoes are of this type, generating fluid lavas that can flow considerable distances from the active vents. These gently sloping volcanoes can destroy property when they erupt, but they seldom cause fatalities. One of the reasons why Usu is considered dangerous is that it has erupted nine times since 1663, and all of them have been explosive, resulting in fatalities and destruction of nearby villages and towns. Practically all of the deaths from Utu's eruptions have been caused by ashfall, mudflows and pyroclastic flows and surges. The pyroclastic flows have the potential to be especially deadly.
Pyroclastic surges are even more forceful than flows.
Whereas flows follow the topography and move downhill, surges, since they're less dense than flows, can actually flow uphill and spill over ridges. Most buildings are obliterated by these flows and surges, and all living things in their path may be wiped out. Pyroclastic flows can form in several different ways. When a lava dome collapses, for instance, the sudden release of pressure can cause an explosive eruption of ash and lava that moves pell-mell down the flanks of the volcano. Laterally directed explosions can also trigger pyroclastic flows, such as occurred on Mt. St. Helens in 1980.