Chi Poon - Geo Postcard

Geyser: Lady Knox Geyser in Rotorua. It was discovered 100 years ago. The structure of the geyser is very unique. It contains a structure that contains two chambers; the top one is occupied by cold water and the bottom camber is filled with hot water about 150°C. These two chambers are separated by a really narrow tube that put a restriction on the mixing of the cold and hot water, so these water chambers remain unmixed and the cold water serves as a lid and put pressure on the hot water making it super-heated.
On the day of our visit, the manager put on a show for us and makes the geyser erupt steam and water (otherwise this geyser has a various natural cycle eruption of 24-72 hours). He puts soap into the geyser, which then generates foam on the cold water lowering the pressure that the cold water put on the bottom hot water chamber allowing the lower chamber hot water to push its way up mixing with the cold water and ultimately erupts steam and water. You might think the erupted water would be quite hot, but it mixes with a lot of cold water and the erupted water is relatively cool. This eruption can last an hour or two, and then eventually the water remaining in the geyser would cool back and the eruption would end, and the heated ground water would slowly to refill the bottom chamber.


South Crater, the Crater Imposter: During the hike of Tongariro, which is a composite volcano (alternating layering of lava and rock fragments). This is a photograph of a crater imposter called the South Crater. It is amazing how the basaltic lava flow naturally formed a crater like rim, so perfectly surrounds an area, which trapped rainfall and snow melt, structuring the area into a sediment basin, which is quite flat. The rainfall and snow melt erode and transport the slope and deposit the more well sorted, finer grained and more rounded sediments at the basin. The “crater” occasionally fills up with snowmelt and rainfall. As you can see in the photograph a little pond of water can still be seen on the sediment basin.