The Geology of Choosing Your Race – Part 2

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October 20, 2015 on 2:13 pm | In Community, Employee Adventures, Life at TriSports.com, Races, Random Musings, Sponsorship | No Comments

This blog brought to you by Team TriSports athlete Liz Miller. As you start looking towards next season and your race selections, you might want to take more into account that just the race course. Liz’s expertise as a geologist gives us some insight into some other areas that might be of interest in your perfect race quest. Check out Liz’s blog or follow her on Twitter – FeWmnLiz.

A little while back, I wrote a blog post called “The Geology of Choosing Your Race.” This is once again a slight departure from the typical blogs found on TriSports.com, but in an attempt to combine two of my passions (geology and triathlon), how about a look at some of the most “geologically-interesting” IRONMAN® and IRONMAN 70.3® races around the world!

IRONMAN® New Zealand

I spent 3 weeks backpacking around New Zealand almost 10 years ago, and I would jump at the chance to go again – it’s a beautiful country with friendly people and TONS of interesting geology. New Zealand is unique in that there is a plate boundary that essentially splits the country in two – the north island and north part of the south island are located entirely on the Australian Plate, and the rest of the south island is located on the Pacific Plate. This plate boundary “dissection” makes for exciting geology!

Tectonic setting of New Zealand, taken from Te Ara: The Encyclopedia of New Zealand

IRONMAN® New Zealand takes place in the town of Taupo, which is centrally located on the north island. The town is located in the Taupo Volcanic Zone, which has seen ongoing volcanic activity for about the last 2 million years. Lake Taupo, where the IMNZ swim takes place, lies within a caldera (Spanish word for “cooking pot”; in geology it means depression or bowl). This caldera was formed approximately 27,000 years ago when a huge eruption took place – so much material was erupted from below the surface that the surface essentially collapsed to form a large bowl, and water eventually filled in the depression to create Lake Taupo.

Lake Taupo, the picturesque location of the IMNZ swim, taken from www.greatlaketaupo.com

The Taupo Volcanic Zone is the world’s most productive area of recent volcanic activity; most of the rocks that are erupted in this zone are rhyolite and have a very high silica content. These rocks are chemically similar to granite, but they solidify above ground rather than below ground. The youngest and most well-known volcano in the Taupo Volcanic Field is Mt. Nguaruhoe (which translates to “throwing hot stones”), which served as Mt. Doom in the Lord of the Rings trilogy. Mt. Nguaruhoe is a composite volcano, which is made of alternating layers of lava and volcanic ash; it started forming only 2,500 years ago, and the most recent eruption took place in 1975.

Mt. Nguaruhoe in the clouds. Photo taken by author in 2006.

IRONMAN 70.3® St. George

A race that doesn’t require a transcontinental trip and yet still has some spectacular geology is St. George. The bike course of St. George takes athletes through Snow Canyon State Park, which contains both sedimentary AND volcanic rocks. The two major rock units at Snow Canyon State Park are the ~200 million year old Kayenta Formation and the overlying Navajo Sandstone (age dating of the Navajo Sandstone is difficult due to a lack of fossils). The Kayenta formation is mostly sandstone, siltstone, and shale (the latter rocks are similar to sandstone, just a little finer-grained); rivers and streams deposited these units.

Mudcracks are just one indication that an area was once subjected to frequent wetting and drying, such as what is found in a river and stream environment. The author recently found this rock with textbook-type mudcracks while hiking in Utah (awesome Pearl Izumi running shoes for scale)!

The Navajo Sandstone contains massive cross-bedding that were deposited in “eolian” (i.e. windy) environment – these were essentially HUGE sand dunes, indicating that the environment during the deposition of the Navajo Sandstone was very similar to the modern-day Sahara Desert. The lower part of this unit is red, and the upper part of this unit is bleached white, resulting in a surprising color contrast in this desert landscape.

Petrified sand dunes in Snow Canyon State Park, Utah. Taken from geology.utah.gov, photograph by Lance Weaver.

In many places within Snow Canyon State Park, volcanic rocks overlie the sedimentary rocks; these rocks are more resistant to weathering and essentially work to hold the lower sedimentary rocks in place by preventing erosion.

IRONMAN® Wisconsin

Have you ever wondered why IM Wisconsin has SO MANY HILLS? Well, you can blame it on the glaciers! Starting 1.7 million years ago, the Ice Age began. During this time, large ice sheets (essentially very large glaciers) formed in Canada and began moving south throughout North America. Madison, Wisconsin, and much of the IM Wisconsin bike course are located in an area that was covered by the Green Bay Lobe of the Laurentide Ice Sheet 25,000 to 10,000 years ago.

As glaciers and ice sheets advance, they incorporate rocks, dirt, and other material. Glacial debris and movement works to shape the landscape over which the glacier is flowing. One common feature that is formed is a drumlin, which is an elongated hill in the shape of an inverted spoon or half-buried egg. The formation of drumlins is still not entirely understood, but they are believed to be a combination of both depositional and erosional processes acting at the interface between the glacier and the underlying surface. Drumlins are one source of hills on the IM Wisconsin bike course.

An aerial view of drumlins. Each of those little ridges is a drumlin, which translates directly into a HILL on the IM Wisconsin course. Taken from www.geo.cornell.edu

The other source of hills is the result of glacial melting and retreat. Glaciers act a lot like a conveyor belt – as material is picked up, much of this material is moved to the bottom and edges of the glaciers. As the climate began to warm, glaciers started to move back towards the poles, where the weather was colder. This material is commonly deposited as an end moraine, which is a ridge-like deposition of debris at the very end of the glacier. In addition, because glaciers don’t retreat all at once, they also commonly deposit recessional moraines, which are end moraines that mark each of the “rest stops” that the glacier took as it retreated. You can blame most of the hills on the IM Wisconsin course on these end and recessional moraines!

All of the dirt resting between the lake in the foreground and the glacier in the background will eventually turn in to a terminal moraine when the glacier retreats. Picture taken by author during the 2005-2006 McMurdo Dry Valleys, Antarctica field season.

I’m sure that on race day, most of us will be too focused on racing to appreciate the geology that surrounds us. But be sure to allow an extra day or two post-race to enjoy the beauty that is often found along many race courses!

Note: IRONMAN® and IRONMAN 70.3® are registered trademarks of World Triathlon Corporation.

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