A tsunami is a wave generated by the sudden vertical deformation of the boundary of a body of water, and can be generated both in the outer ocean or in enclosed water areas such as bays and lakes (see Sections 2.7 and 5.3). There are several potential causes of the deformation of land masses which can generate a tsunami. Figure 5.1.1 shows the causes of tsunami events that claimed at least one death from the year 1900 to 2020, based on data from the NCEI/WDS Global Historical Tsunami Database (National Geophysical Data Center/World Data Service n.d.). Earthquakes, landslides, volcanic eruptions, or the combination of these geological activities, have all caused tsunamis in the last 120 years, though these events were predominantly caused by earthquakes.