We present a simple time-progressive model for the Hawaiian Island chain bathymetry and the associated flexural response of the elastic oceanic lithosphere. The model is used to study the vertical tectonic history of Cross seamount, a Cretaceous guyot brought close to the Hawaiian hot spot by plate motion. Geological evidence indicates that Cross was truncated at sea level, but its flat top is presently 400 m below sea level. Our reconstruction suggests the seamount was elevated on the Hawaiian Swell and truncated about 3.2 m.y. ago. The post-truncation subsidence is attributed to the flexural moat that developed around the growing Hawaiian Islands. Flexural isostatic adjustment explains the current depth of Cross seamount provided the elastic plate thickness is in the 30--35 km range.