Since the PTWS operates on the basis of seismic data it contains no formal mechanism for dealing with the rarer tsunamis generated by landslides, volcanic eruptions or impacts. Although both impacts and landslides and many types of volcanic eruption will generate seismic signals, only the very largest events will exceed the Ms > 7.5 threshold. Submarine landslides and impacts are a particular problem because at present they are likely to happen with little or no warning: this is also true of many volcano lateral collapses.