The Top Five World Geologic Sites

Author:  Phillips Veronica

Date:  January 2008

To study the Earth is to study the present in order to make inferences about the past and predictions for the future. The understanding of geology is more than just to provide scientific background for major blockbuster disaster movies like "Volcano" or "The Core" (not that either of these films can boast any sort of satisfactory basis on science), but to help the general public prepare for potential natural disasters as well as attempt to mitigate the effects that might trigger them.

Geology is unique in that its features are usually accessible and can be readily observed all over the world. Ask any scientist with a background in Earth Science what they think the five most significant geologic sites are and you may be surprised at how well they agree,or not. Peter Schiffman, igneous petrologist for the University of California at Davis and visiting professor at the University of Edinburgh; Patience Cowie, a reader in structural geology at the University of Edinburgh; and Hilde Schwartz, a lecturer at the University of California at Santa Cruz with a background in vertebrate paleontology, environmental geology, paleoecology, were kind enough to volunteer their lists of geologic sites worthy of special notice. Below, in no particular order, is a compilation of the sites that should not be missed.

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Siccar Point, Scotland, UK

In the Western world, interest in geology was fuelled in the seventeenth century by the debate between naturalists and the Church about the origin of the Earth. Prior to this time, most scientists had attributed the cause of all landforms to Noah's Flood and had accepted that the age of the Earth was only a few thousand years old. Enter James Hutton, today considered to be the father of modern geology. Hutton observed that certain processes, if assumed to have occurred in the past at the same rate as the present,called the Principle of Uniformitarianism,occurred too slowly for the Earth to be so young. One of several localities said to have inspired Hutton's deductions about the nature of geologic processes is at Siccar Point along the Berwickshire coast. During his visit in 1788, Hutton noticed nearly vertical shale strata overlain by sub-horizontal layers of sandstone (see picture). Hutton recognized that the formation's appearance indicated a long cycle of deposition, burial, tilting and uplift, erosion, and further deposition after another period of burial. Thus, where the two rock types meet represents a gap in time, where over 50 million years' worth of rock missing from the record. This gap came to be known as Hutton's Unconformity. Because it demonstrates many of the fundamental principles of geology, Siccar Point has been the destination of many an introductory geology class in the UK as well as professionals and geotourists for over two hundred years. For its impact on the development of geology and the view of the age and origin of the world, Siccar Point definitely earns its spot on the list of top geologic sites.

Kilauea, Hawaii, USA Image Courtesy of Peter Schiffman, UC Davis

Kilauea, Hawaii, USA Image Courtesy of Peter Schiffman, UC Davis

Kilauea, Hawaii, USA

Kilauea is near to a volcanic equivalent to Old Faithful. Though there might not be a pattern of regularity in the eruptions, they have been almost continuous in recent years. For Schiffman the appeal is in that Kilauea provides "volcanism on a reliable basis in a place that's relatively safe and accessible." Due to its position on the flank of the towering Mauna Loa volcano, Kilauea appears inconsequential in comparison.

Schwartz stresses that Kilauea's significance lies in that, like Iceland, Kilauea is the most recent outlet for an active hot spot. In fact, this same hot spot formed the rest of the Hawaiian Island chain as the Pacific Plate migrated over it through time. Consequently, Kilauea undergoes a less explosive sort of volcanism than other volcanoes like Mt. St. Helens and forms comparatively flat domes of basalt. Based on evidence of places like Kilauea, geologists determined that the different shapes, sizes, and compositions of volcanoes around the world are formed by different processes and offer insight on how the Earth operates beneath its surface. Since it confirms that the study of the Earth is not superficial, the Kilauea volcano makes the cut for geologic locations to visit.

Moine Thrust, Scotland, UK Image Courtesy of Rob Butler, Leeds University

Moine Thrust, Scotland, UK Image Courtesy of Rob Butler, Leeds University

Moine Thrust, Scotland, UK

Scotland has long been revered as a sort of geological Mecca, and rightly so; many of the fundamental principles of the science were worked out on Scottish soil, often with little information other than that afforded by observation. The concept of duplex thrust geometry fits into this category, and while further explanation of this is beyond the scope of this article, a prime example of it is the Moine Thrust Zone. First mapped in 1883, this region is usually the first a structural geologist will mention as a classic structural locality,structure meaning the features, such as folds and faults, which indicate the nature of the deformational processes operating on a rock. Running for 190 kilometers down the northwest coast of Scotland, the Moine Thrust is an example of a type of fault that forms as a consequence of stresses that compress the continental crust and push older rock on top of younger rock. When this locality was first studied, geologists had to create a scenario that would explain why rocks of Cambrian age were sandwiched between much older Precambrian aged ones. From observations of rock outcrops along the fault, they characterized the expected geometry of the Moine Thrust based on quantifiable parameters, a concept that could be applied to any thrust fault. As another example of the pioneering work done by early geologists in Scotland, the Moine Thrust Zone is definitely worth seeing.

Semail Ophiolite, Oman Image Courtesy of the BGS

Semail Ophiolite, Oman Image Courtesy of the BGS

Semail Ophiolite, Oman

Any ten-year-old with a world map and a pair of scissors can see that when cut out, the shapes of the continents fit together quite nicely. Their present location was explained to be an effect of plate tectonics. From the modern perspective the validity of this concept is almost absolute, but in the early twentieth century the idea that the continents moved around was far from being accepted. Some credence was given to the theory of plate tectonics in the late 1950s when radar imaging of the Atlantic revealed magnetic anomalies in the rocks parallel to symmetric about the Mid-Atlantic Ridge.

Though they were discovered in the early nineteenth century in the Alps, ophiolites were not recognized as assemblages of ocean crustal material emplaced on land until geologists sought further evidence in support of plate tectonics. "Ophiolite exposures in Oman might be the best in the world," says Peter Schiffman. He highlights their role in the eventual acceptance of plate tectonics. "Assemblages of pillow lavas and sheeted dikes are basically indicative of ocean spreading centers now found on land, and the only way to explain that was plate tectonics."

Though not perhaps the most revolutionary theory in the history of geology, plate tectonics is still very significant as a means of accounting for a range of geologic wonders. As a key instrument in the acceptance of this theory, ophiolites make the cut for a top geologic site to see.

Grand Canyon, Arizona, USA Image Courtesy of Katie O'Brien, UC Santa Cruz

Grand Canyon, Arizona, USA Image Courtesy of Katie O'Brien, UC Santa Cruz

Grand Canyon, Arizona, USA

The Grand Canyon is frequented as a tourist attraction for its rare natural beauty, but geologists value it for an additional reason. Since the Colorado River began cutting into the Colorado Plateau about 5 million years ago, it has exposed in the canyon walls about two billion years of almost uninterrupted geologic record. "You can really gain an appreciation of deep time' as well as the erosive ability of rivers," says Peter Schiffman. Schiffman believe that the Grand Canyon is a perfect example of the juxtaposition of old and young. "You can see rock layers that represent a large span of time exposed by an active process."

Beyond its testament to time, the canyon's relationship to other geologic processes that shaped the entire western margin of North America is important to geologists. Indeed, if it were not for the mountain-building events that formed the Rockies, the tectonic uplift that formed the Colorado Plateau, the thinning of the continental crust as western North America was stretched due to tectonics, and the opening of the Gulf of California, the Grand Canyon might not exist at all. The well-preserved exposures on the canyon walls allow geologists to infer the climatic and tectonic conditions that would explain the type of sediment,e.g. marine or desert,deposited in the record. For its use as a geologic storyteller and magnificent beauty guaranteed to please every eye, the Grand Canyon is included as a top site to visit.

"We have no vestige of a beginning, no prospect of an end.",James Hutton, Theory of the Earth

Written by Veronica Phillips

Reviewed by Antje Heidemann, Pooja Ghatalia

Published by Pooja Ghatalia.