Mud Pool
Due to thermal activity on the North Island many mud pools, such as this one, pop up in Rotorua. Ash and debris from volcanic eruptions collect and can form smectite clay which is sticky and gooey. The clay expands or contracts depending on the temperature of the water within its layers. Hot water, which is heated by underlying magma close to the surface, rises. Magma is close to the surface in this area due to tectonic activity. Heat then travels up the path with the least resistance leading to certain spots in the mud pool to bubble. Steam from the heated water can be seen coming up from the mud pools. Areas with debris and high concentrations of water can lead to this geothermal phenomenon.
Lake Pukaki
This is an example of lakes formed by glaciers. Ice has incredible erosive power digging down into the surface and carrying rocks and debris along with it. When the glacier reaches a certain position and stops in one place it deposits some of this material to form a terminal moraine. After the glacier melts and recedes this moraine can dam up water forming a lake. Glacial lakes tend to be long, narrow and deep. In the case of Lake Pukaki it was formed by glaciers from Mount Cook which now are receding. Braided rivers made up of glacial melt waters feed the lake. Pukaki is a brilliant blue color when the sun is out due to glacial flour from the river. Glacial flour is small sediment particles formed by the grinding of rocks from ice movements. The fine particles are suspended in melt water and reflects this blue color when sunlight hits it.
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