Torie's Geo Postcards

LADY KNOX GEYSER

On November 17th we visited the Lady Knox Geyser in the Wai-o-tapu geothermal area. Originally the geyser was discovered in 1901 by prisoners who were clearly vegetation in the area to make room for the planting of pine trees. When the geyser was first found it did not have the tall snout on it that you can see in the picture above. The snout was added later as an effort to make the geyser spray higher. The geyser has two chambers of water underneather the ground, one cooler upper chamber and one warmer lower chamber. The upper chamber is cooler because of its proximity to the outside air and never exceeds boiling point and the lower chamber is warmer because of the hot magma underneath it and is about 150 ° C. Naturally the Lady Knox Geyser would erupt every 48-72 hrs but thanks to the help of some park rangers the geyser erupts every morning. Around 10 am the rangers add soap the the throat of the geyser and within minutes the geyser erupts sky high. The reason soap causes an eruption to occur is because it lowers the surface tension of the upper chamber and allows the two chambers to mix together. When the chambers mix together it causes the pressure within the geyser to increase and the only way to release the pressure is to force it up and out the throat of the geyser, causing an eruption! This Geyser is similar to our OLD FAITHFUL in the States!

REVERSED GRADIENT

On our last in New Zealand a colleague if Don Rodbell's, Jamie, came out to Twizel and showed us around the Tasman Glacier and a few outcrops. The out crop above was the second outcrop we looked at and was of a terminal moraine. With in the picture you can see fine well sorted sediment on the bottom of the cross section and bigger, poorly sorted sediment on top. This is known as a reversed gradient or a reverse grading system because normally what we should see is bigger boulder pieces on the bottom and smaller, well sorted sediment on top because heavier boulders fall out of suspension first. The reason this outcrop is different than normal has to do with glaciers. When a glacier does what is known as a glacier leap and bobs above the ground that it is stuck to and allows sediment to pass through the gap between the glacier and the ground. Since the glacier normally only has a small space between the bottom of the glacier and the ground only fine, well sorted material can pass through this gap and then settle out farther down stream. When the glacier gap gets bigger then bigger material is allowed to flow between the gap and thus creates what we see above, a reversed gradient where smaller, more well sorted particles of sediment are at the bottom and bigger, more poorly sorted particles are at the top. This outcrop was my favorite outcrop we looked at beause it truly showed me how sediment cross sections can really tell a story of the history that occured in a particular area!!