AN INTERNAL SEICHE IN LAKE ROTOITI

should note that for various sound theoretical reasons a lake during the summer becomes divided into two layers each of relatively uniform temperature separated by a region in which the temperature, and thus also the density, changes rapidly with increasing depth. Fig. 2 shows a number of graphical representations of this type of temperature change. The uniformly heated, warm, upper layer is known as the epilimnion; the layer of rapid temperature change with depth the thermocline or metalimnion, and the uniformly cold bottom layer the hypolimnion.