A pyroclastic density current (PDC) is characterized by its strong stratification of particle concentration; it consists of upper dilute and lower dense currents, which control the dynamics and deposits of PDCs, respectively. To explain the relationship between the dynamics and deposits for magmatic and phreatomagmatic eruptions in a unified way, we have developed a two-layer PDC model considering thermal energy conservation for mixing of magma, external water, and air. The results show that the run-out distance of dilute currents increases with the mass fraction of external water at the source (w_mw) owing to the suppression of thermal expansion of entrained air. For w_mw~0.07–0.38, the dense current is absent owing to the decrease in particle concentration in the dilute current, resulting in the direct formation of the deposits from the dilute current in the entire area. These results capture the diverse features of natural PDCs in magmatic and phreatomagmatic eruptions.