Sarah Allen - Postcard 1

November 19, 2007
Lake Taupo Terraces

Lake Taupo occupies a caldera, a collapsed volcanic chamber that erupted in AD 186. The caldera is much larger than the current lake level and this can be seen with the wave cut terraces (benches) that circle the lake. This photo, representing approximately 2 meters in height, shows one of these terraces. The interpretation of this site is not finite – it involves multiple working hypothesises, a common practice in geology. It could be the former edge of the lake, a fluvial or stream deposit, or a combination of both. The white pumice cobbles are well rounded and imbricated or shingled on top of each other, which is indicative of stream transport. The alternating layers of pumice and fine grained, well-sorted, sandy silt (possibly reworked volcanic ash) demonstrate a change in the energy of the system. Typically, larger particles need a higher energy environment to be moved and deposited, but it may be reversed in this case, since pumice is so porous that it floats. The fine material could also be floodplain deposits from the lake or a stream. The former shorelines/terraces can be correlated around Lake Taupo. The changes in lake level may be due to climate change, erosion, or a newly formed outlet.

Mud Pools--> Rotorua, New Zealand In this area mud accumulates from volcanic ash over a geothermal active area. The heat source from underground heats up the turbid water, which rises towards the surface. This causes the bubbling of mud upwards, sometimes with great force spewing mud all over the place. This is an unstable area that can be very dangerous. The mud here is used for face masks, because it absorbs excess oils and impurities from within the pores, leaving smoother, softer skin. This absorption is due to the clay, which shrinks when it is dry and expands when wet. You could see the steam rising out of the mud, hear the bubbling burp noises, and smell the taint sulfur scent.



Kura Tawhiti Conversation Area--> These towering rocks referred to as Tors underwent long-term chemical weathering and are post glacier landmasses, so they are rather old. They are sedimentary rocks with some horizontal layering present but difficult to really see due to the years of erosion. More specifically these large boulders are remnants made up of limestone. Limestone is more easily corroded in natural acids than other rocks which gives the structures a scalloped rough surface. The boulders are broken by joints where water percolates and erodes, leaving these striking towers that stick out of the ground. The area is also an important site for the Maori people of the New Zealand, leaving rock art throughout the incredible landscape.

Mt. Ruapeho is an active composite volcano made of alternating layers of ash and rock. The rock type consists primarily of andesite and boulders that are strewn far and wide across the landscape indicating its prolific activity: it has a significant eruption every few decades with smaller one occurring more frequently with the last one in September 2007. Crater Lake sits in the mouth of the volcano and has a pH of 1 (greater acidity than the acid in stomach) and a temperature of 38◦C. The amount of water in the lake effects how large the resulting lahar will be and allows geologists to map where the lahar will flow. Lahars going down the volcano can attain speeds of 90 km/hr and can create devastating effects. Due to the volcano’s reach into the upper stratosphere, the volcano is often snow-capped and is used as a ski resort. The class hiked up Mt. Ruapeho in ~6 hours and went down the mountain in less then 2 hours thanks to the ability of trash bags to be used as sleds.

White Island was named by Captain Cook as he only sailed past it and didn’t explore it further as he would have found an active, stratovolcano created by pyroclastic lava flows and lahars. By visiting the volcano, one is able to stand on some of the newest continental crust on the earth which consists mostly of andesite and tefron deposits. White and yellow patches likened to a pie (cool crust and a hot center) dot the landscape and these colors are due to gypsum and sulfur, respectively. Fumaroles are also strewn across the island the mouth of the volcano has a dynamic lake that has dropped 30 meters in the span of 6 weeks. The lake is quite dynamic with its color changing constantly and its temperature ranging from 30-70◦C depending on its height. Due to the high concentration of hydrochloric and sulfuric acids, the lake has a pH of -0.6. The water in the lake comes from steam cooling and the lake can be a concern as if it rises too high and spills into the ocean, the abundant and diverse marine life surrounding the nutrient rich island would be damaged. The volcano was mined for its sulfur in the early 20th century and is now studied and monitored by scientists with a seismograph and web cameras located on the island and also by monitoring gas emissions. On the volcanic alert level that scales from 0 to 5, White Island volcano is given a 1. The highest point on the volcano is 321 meters high and is named Gismund Point.

Otira Valley on the South Island of New Zealand is a geologically active area. High erosion, uplift and rain lead to a lot of relief, high valleys and unstable slopes. These create frequent and intense landslides, posing serious threats to those who drive through this area. It is believed that there was one seismic event that caused the major destruction in this valley. 186 A.D. was the last major Taupo volcanic eruption, which probably had caused enough seismic energy and shock to initiate an epic landslide. Charcoal was found and dated back to 1900 BP, showing that the Taupo eruption could have a strong connection to the origin of the landslide. A viaduct was created in the valley to stabilize the road, as it previously built on top of a landslide. This project cost $25 million and was constructed over 2 years. This viaduct was created because it is well-resistant to earthquakes and is minimally affected by erosion from landslides. The viaduct can withstand earthquake stresses 40% more than all other forms of protection created in New Zealand. There are also V-supports that reflect landslide debris, these supports are visible on the 2 end piers, but not in the middle pier because this is not a big path for landslide debris. The overlying problem is that the alpine fault goes through this valley so it is very geologically active; this is one of the most tectonic areas in the world because of increased precipitation, uplift, and increased relief of unstable slopes. All of these characteristics make it very unstable and an area of concern, which is why the viaduct was created. A road was initially created in this unstable valley in the 1860s for transportation and took 18 months to create.

-By: Jordan Silletti

Katie Premo

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.

Fox glacier is located near the west coast of the South Island of New Zealand. It is 6-8 kilometres in length, blue in colour, striated, and covered with sediment. There are four essential elements to creating and maintaining a glacier, high precipitation, wind, snow, and elevation. Tectonic activity is essential because it allows for the high elevation. The alpine fault pushes the mountains up; giving Fox Glacier the elevation it needs to survive. The valley is V-shaped and has nearly-vertical rock faces created by the advancement of the glacier. Seracs, which are created when ice movement slows, piles up on itself and fractures, are visible at the top of the glacier. The debris and rocks carried by glaciers create lateral and terminal moraines. These rocks are haast schist grading into gneiss as they get closer to alpine fault. Throughout our visit we saw many boulders falling off the face of Fox Glacier, showing how unstable and unsafe it is to be near glaciers. Water melts from the ice carrying a lot of sediment and finds a path out, the melt water flow is called end glacier tunnels. The flow is constantly changing between calm and raging; a high flow rate allows movement of huge boulders. Large floods can occur if “plumbing” is backed up and has a sudden release of water; this is called a jokallahap. Surging glaciers are also able to advance fast down valley because the pressure of melt water under the glacier forces it to de-stick from bedrock, allowing it to surge down valleys hundreds of metres. Dead ice, which is ice left behind because a glacier moving so fast, is also visible at Fox Glacier. This ice can survive for decades because it is buried in outwash, providing insolation. Kettle lakes are circular lakes that form around dead ice. An alluvial fan formed in the valley from glacier advancement which previously kept the sediment in place. The waterfalls visible throughout the valley are created by hanging valleys. Waterfalls are typical geological feature of glacial locations because side valleys hang above the main valley, which is eroded faster because it has more ice than side valleys. My 2 pictures are of Fox Glacier 1 year apart. Some of the most obvious differences are there is more sediment on the glacier November 2007, since December 2006 a lot of the snout has melted, the velocity of the melt water in December 2006 was a lot stronger, there appears to be a lot more snow accumulation on top of the glacier in November 2007, and the seracs are more defined in November 2007.

photo on left: Fox Glacier November 2007

photo on right: Fox Glacier December 2006

-By: Jordan Silletti