Brandon McArdle's Postcards

Hey Mom, We just got to New Zealand and one of the first things that we did was to go to the Wai-o-Tapu geothermal area. It is a major geothermal area focused around Rotorua, in the north Island of New Zealand. One thing they showed us was a mud pool, and it was really cool. It is a geothermal phenomenon which occurs in geothermally active areas where there is a volcanic ash and sediment deposit. A magmatic heat source heats the ground water and causes it to rise to the surface. On the surface is a concentration of ash and other debris such as volcanic glass. The hot water mixes these deposits to create a substance called smectite, which is an expandable clay. An example of one type of smectite is called bentonite. Water causes it to expand because it is so polar. The water molecules build and stack on one another expanding the clay up to 10 or more times. This clay is very gooey and can even be used instead of soap. Looking onto the pool you may notice a bubbling which occurs in only certain areas. This is caused by heat which is able to break through of areas of least resistance creating a crack in the bedrock. This causes a continual escape for the heat and pressure which makes the bubbling effects. A mud pool is a much safer and less destructive release of the heat and pressure as opposed to that of a volcanic eruption because it is much more minor and constant. It also has a really bad sulfur smell which is from the release of hot magmatic air from below the surface of the earth. I know it doesn’t sound it described like this, but it is really cool. See you soon.

Love, Brandon

Hey, Mom. We made it to the South Island and we went to the Fox Glacier. It was really incredible. On our way back we saw a piece of ice left over from the glacier and the professors told us what is was. When a glacier recedes too quickly from getting too hot too fast, occasionally large pieces of ice will break off. Because they are no longer a part of the moving glacier it remains stationary. Over time glacial out wash and other debris cover that leftover piece of ice. Eventually, the ice melts completely, and when this happens the land created over the ice collapses to create a lake which is called a kettle lake. These lakes can be found all over the north east of the United States, like around where we live! Well, I’ll be home soon.

Love, Brandon

Jenny Zhao

The above photo was taken by the Mueller Glacier. At the bottom of this mountain, there are alluvial fans. These alluvial fans formed quite a while ago seeing as how there is vegetation growth on them. Alluvial fans are made up of sediment brought by streams of water that accumulate at the base of mountains. Near the base of a mountain the land is more leveled, resulting in the slowing down of the water flow. As the velocity decreases, the streams’ ability to carry sediment also decreases. Thus, sediment is laid down. Alluvial fans are usually graded, with coarser sediments closer to the base of the mountain and finer sediments near the edges of the fan.


Shown in this photo is a huge chunk of dead ice. This photo was taken by the Fox Glacier. Sometimes when a glacier moves quickly chunks of ice may fall off and get left behind. With time the stagnant ice gets buried under sediment (perhaps from alluvial fans or talus close by). The pressure from the pile of sediment helps to preserve the ice. Preservation of ice can last for decades. In the photo the edge of a kettle lake can also be seen. Melting of dead ice contributes to the forming of a kettle lake.

Lisa Angotti's Geo Postcards

The above photo, taken at Wai-o-tapu Geothermal Field in Rotorua on the North Island of New Zealand, shows an area called the Primrose Terraces. The millions of small terraces, which appear as small 'steps' in the sediment, are formed when water overflows from the Champagne Pool, another nearby formation. The Champagne Pool is a collection of hot (74 degrees Celsius) water filling a 62 metre deep explosion crater lined with sinter, a chemical sediment or crust deposited by a mineral spring (Random House Unabridged Dictionary). This sinter dissolves into the hot water as high-concentration silica. When the water from the Champagne Pool overflows, spilling over the area now known as the Primrose Terraces, it cools as it travels, and much of this silica precipitates out as sinter, coating the landscape and forming these terraces. The Primrose Terraces cover about 3 acres, making them the largest in the southern hemisphere, and they have been forming for about 700 years since the formation of the Champagne Pool.






The photo above shows an interesting rock type known as pumice. This rock is an extremely light and porous piece of volcanic debris, formed when volcanic lava cools quickly, leaving large pockets of air trapped inside. The lava hardens around these air pockets, leaving large holes in the rocks formed. Because they have so many air pockets, the rocks are extremely light. For example, the pumice in the picture above, larger than the palm of my hand, weighed little more than a sponge of the same size. Because pumice is so light and has a very low density (due to the large amount of air pockets in the volcanic material), pumice floats (see picture below).

The above photo is of the same piece of pumice floating in Lake Taupo. Because the pumice floats, it is easily transported by water movement, even at very low velocities. Because of this unique feature of this rock type, locations of pumice deposits are often used to identify locations of former water movement. In the case of Lake Taupo, pumice deposits far offshore from the current location of the lake are one of the factors used in identifying terraces which mark former lake levels.

The shores of Lake Pukaki offer clues to the formation of the landscape. In this embankment, which has been exposed through erosion, many layers of sediments deposited at various times and under various conditions of the area are shown. The layers, which were deposited indirectly through glacial action, are not the typical glacial deposits of moraines. These beds were formed in fluvial outwashes from the glaciers as they expanded and retreated at various times.

Dan Bailey's Geo Postcard

Greywacke and Shale Road Cut

The above photo is of a road cut along State Route 73 to the east of the Southern Alps. This road cut consists of greywackes and shales of the Torlesse Supergroup. These rocks are sedimentary rocks resulting from the lithification rock fragments and sand in a clay matrix that made up the original New Zealand geosyncline. This sedimentary rock was then subsequently uplifted, twisted and turned, and brought to the surface by the Rangitata and Kaikoura orogenies.The rocks in this road cut showed several interesting sedimentation features. This rock outcrop showed graded bedding. The graded bedding arose from variable velocity underwater or marine mudflows that deposited sand, silt, and clays in layers that were graded from the coarsest/densest grains to the finest/lightest clay sediments. This mechanism of deposition gives rise to sole markings, where the densest/largest debris is dragged along the bottom of a flow gouging the freshly deposited mud layer below it. These gouges or scours are then infilled by coarser sediments, yielding a “cast” of the original marking. Once the sediments are lithified and the shale layer is eroded away, the sole mark becomes visible. The specific type of sole marking shown in the above photo is a symmetric grove cast, which can be used to determine the trend in flow direction.The graded bedding can be seen with the dark fine clay grains (almost black in the lower right) above the lighter brown coarser sand grains (in the middle) with another dark clay layer below in the upper left. The prominent ridge seen in the coarse brown layer is a grove cast indicating the trend in direction of the mudflow that deposited these sediments. The whole rock formation was uplifted from its horizontal orientation of deposition to its current nearly vertical orientation on the road cut.

Kura Tawhiti Conservation Area

The above photograph was taken at the Kura Tawhiti Conservation Area also along State Route 73 just east of the Southern Alps. The photo shows a rock formation that is known as a tor. A tor forms when a continuous layer of rock is eroded and weathered, leaving the most resistant rocks protruding from the landscape. Tors are usually made of granite or weather resistant metamorphic rocks. What makes this rock outcrop so interesting is that it is made out of limestone, which is particularly soft and susceptible to chemical weathering. This rock started as a continuous layer of sedimentary limestone. The layer became exposed during the last mountain building event and was chemically and freeze-thaw weathered in the rounded/scooped manner characteristic of limestone. This rock outcrop must be relatively young for two reasons. First, limestone is a soft rock that is susceptible to chemical weathering and would be completely eroded away if it were exposed for too long. Second, glacial activity during the last glacial maximum would have destroyed this susceptible surface formation. Therefore, is must be younger than about 10,000-12,000 years old. The rock outcrop is now a popular attraction for tourism and bouldering (type of rock climbing characterized by short, technical climbs without a rope).

Liz Nyberg -Geo postcard

Lady Know Geyser: This geyser, located at wai-o-tapu (sacred water), was discovered in 1901 by prisoners. These newly relocated prisoners were allocated the job of clearing and planting pine trees. The prisoners used the geyser to wash their clothing when they found out that they could make the geyser erupt by adding soap. The cone shape of the geyser was formed by silica accumulating on rocks placed around the geyser base to make the water spray higher. The natural eruption cycle is every 48 to 72 hours, however, when artificially induced it erupts daily at a designated time. The geyser is caused by a heated reservoir underground comprised of 2 chambers. The bottom chamber is 150 degrees C and the upper chamber does not exceed boiling. The upper chamber acts as a lid to keep the hot water down. When soap is added, it softens the water in the upper chamber and it mixes with the lower chamber causing an eruption that can reach up to 20 meters and last for up to an hour depending on weather.
Fox Glacier: This glacier drains from Mt. Cook and flows toward the west coast of New Zealand. Characteristics of this glacier include the seracs or the towers of ice formed on top of the glacier and trim lines from former lateral moraines. There is also melt water at the bottom of the glacier that is produced from midglacial tunnels in the middle of the glacier. There is dead ice further down the valley that is evidence of glacial recession. Dead ice are blocks of ice that have been left behind by a retreating glacier and were insulated by the outwash debris. Occasionally glaciers can get clogged and when finally released it causes a huge flood. Surge glaciers happen when too much pressure builds up and force the glacier to move abnormally fast. This glacier is advancing due to accumulation of increased snowfall (ablation) which is shown by the layering of dust bands.

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.