Scaling analysis and experiments are used to study the evolution of th
ermals in the presence of background rotation. When the ambient enviro
nment is homogeneous, the thermal rises and expands until it reaches a
critical height where the Rossby number becomes approximately 1. The
thermal then stops expanding and rises in a column. Both the critical
height and column radius scale with (F0f-2)1/2. F0 is the initial ther
mal buoyancy and f is the Coriolis frequency. The thermal vertical vel
ocity is independent off. When the background is stratified with buoya
ncy frequency N, the thermal rises to a neutral buoyancy level which s
cales with (F0N-2)1/4. For N/f < 0.6 column formation occurs before th
e thermal reaches the neutral level. For N/f > 0.6 the thermal reaches
the neutral level before rotation is important. In both regimes, geos
trophic adjustment eventually causes the formation of a baroclinic vor
tex consisting of an anticyclonic lens of thermal fluid at the neutral
level and cyclonic circulation below. The lens has Nh/fl is similar t
o 1. The lens thickness 2h and the radius l obey relations of the form
(F0N-2)1/4(N/f)m. However, the exponents m are different in the two r
egimes. The relevance of these results to deep-ocean convection and hy
drothermal venting is discussed.