In this video from Periodic Videos we look at the reaction of Caesium in Water.The reaction is 2Cs + 2H2O → 2CsOH + H2. However, the H2 can then react with O2 in the air to explode. Also, unlike the other alkali metals, except perhaps Francium, Cs is a liquid just above room temperature so the initial heat of reaction will melt the metal and one has liquid metal reacting with the water.