Monday, July 25, 2016

Moher, Moher, Moher!

Well it's been more than a week for this current blog post, but it will be worth the wait, I promise!

Continuing west in Ireland from our previous blog on limestone lies a famous tourist attraction that is evidence of years and years of geological formation. The Cliffs of Moher are an amazing feature along the west coast of Ireland in County Clare. The story behind these cliffs is incredibly complex and demonstrates what a bit of geomorphological and geological processes can achieve given a lot of time. Intrigued? Allow me to explain, but first let me to introduce a visual of this stunning area!


Beautiful, eh? Well, what you are looking at is essentially many years of deposition along a river delta.  A river delta is where the end of the river meets a "non-moving" body of water like sea or a lake. At this location all the sediment that traveled with the river deposits are the current that transported the material stops. Typically we think of river deltas as being very flat areas found at sea level. In the case of the Cliffs of Moher, repeated sediment deposition (5 different major events) in conjunction with sea level changes and tectonic uplift created this unique geological feature. The Cliffs formed during the Upper Carboniferous period approximately 300 million years ago. The 5 mile stretch of coastline reaches 700 feet above sea level at its highest point just north of O'Brien's Tower.

O'Brien's Tower built in 1835 along the Cliffs of Moher.

So getting back to the sediment deposition at the Cliffs, striations or layers of rocks can be seen along the exposed walls. What you are seeing pictured below are sandstones overlaying, siltstones on top of mudstones. The darkest layers are the mudstones. These layers are what you can see from the edges of the Cliffs. Below these rocks are the Clare Shales and yes, evenutally the limestone we talked about previously is located below the shale.

The Clare Shale Formation is approximately 40-50 feet thick and contains phosphate, carbonate nodules, and chert (silica based rocks lacking a typical repeating pattern of mineralogy). Fossils can be seen in these rocks as well. This time period had a very slow deposition of clays at the bottom of a deep basin (keep in mind the continents were still moving around during this time and what we presently know as Ireland was located near the equator ). Above the Clare Shale begin the sedimentary rocks that we know as the Cliffs of Moher. As mentioned there were five repeated deposition time periods where mudstone, siltstone, and sandstone layers were deposited. However, only two of these time periods or "cyclothems" can be seen in the area. Each mudstone layer is 23-60 feet deep followed by 115-260 feet of siltstone and sandstone. The sandstone and siltstone contain fossils,  water ripples suggesting waves in the basin, and tunnels from creatures living in the material before it hardened into rock. The siltstone and sandstone come from river flooding events depositing eroded materials from the land. The mudstone is evidence of sea level change from glacio-eustatic events (melting and freezing of polar caps and glaciers) as the mudstone is marine.

The Cliffs of Moher contain rocks that are susceptible to weathering and eroding. Overtime the sandstone will be a bit more resistant to the elements than the mudstone, which can cause collapse and further destruction of the Cliffs. It is hypothesized that the Cliffs were located as much as 4 miles further west. This rate is based on the coastal recession rates of the nearby Aran Islands, that is receding at approximately 16 inches per year! It's a great time to go visit Ireland, so take in this amazing place before it's gone've got some time!


Wednesday, June 15, 2016


Ireland was once at the bottom of the ocean. Yes, that's right, Neptune, mermaids, singing crabs, and all that (well maybe not so much singing). Because of our shelled friends, this resulted in an accumulation of calcite or calcium carbonate (CaCO3) in the material that fell to the ocean floor. Limestone is a sedimentary rock, which is a rock that is formed from deposition of sediment that is ultimately compressed and cemented together from pressure. In the case of limestone the pressure exerted comes from the ocean water. The deeper the water the greater the pressure. Limestone in Ireland formed during the Carboniferous period (360 to 300 million years ago). The climate was  tropical in Ireland at this time (think Bahamas!). In addition to calcite, other minerals were present in the sediment giving the rocks that formed a grayish color as shown in the pictures below. As Ireland is obviously no longer under water these rocks are now at the surface and predominate the countryside. They can be seen in both their original position (hillside) as well as used for rock walls that act as confines of pastures for grazing animals.

Limestone hills and walls on the road south of Kinvarra, Co. Galway, Ireland.

A feature that goes hand in hand with the presence of limestone are "karsts." These form as a result of dissolution (minerals dissolving from the presence of water). This process creates "karst landscapes" where the rocks that have spaces in between where the less soluble (more stable) rocks remain. This is demonstrated in the picture below.

Poulnabrone Dolmen in Co. Clare, Ireland.

However, one of the most exciting features of karst landscapes are the caves! Limestone caves in Ireland have many interesting features. Where the calcium carbonate dissolves, it forms different morphological features that you may be familiar with from grade school geology,  namely stalactites and stalagmites. Before these formations reach their identifiable stages, there must be accumulation of calcite, which can look a bit messy initially.

Calcite (calcium carbonate) deposits from limestone in Aillwee Cave.

More calcite deposits on the Aillwee Cave wall.

...And given the right conditions these deposits can form some amazing features inside the cave!

Doolin Cave Co. Clare, Ireland

This impressive 24 foot calcite stalactite is the longest in the Northern Hemisphere. It was not discovered until 1952, when two brave (and slightly nutty) members of a caving club decided to crawl through a small opening and tunnel in complete darkness (to save their torch fuel). Their efforts were rewarded though as you can see in the picture above.

Directly below this feature should be an equally impressive stalagmite. However, due to geological shifting the mass did not accumulate vertically. Instead some sliding occurred and what you see below is the result of thousands of years of calcite accumulation. This feature is only about a foot tall. The sloughing off to the right is the mass that should have formed the stalagmite.

Doolin Cave Co. Clare, Ireland

Knowing a bit about the scientific processes behind the geology just adds to the wonder of this country. The limestone in western Ireland creates an austere yet beautiful landscape both above and below ground. It was impressive to find plants growing in these formations, but as always, nature finds a way! Tune in next week for another look at geology in Ireland...The Cliffs of Moher!

Tuesday, March 22, 2016

Peanut Butter and Gelisols

It's teaching time again! I am in my third year of teaching Introduction to Soils to college students at a university in California. When I came to California in the fall of 2002 for graduate school, I took introductory soils as part of my degree requirements. However, I had no idea how this class would alter my world view. I can't drive, walk, or ride my mountain bike anywhere without noticing the soil and its characteristics. This is especially helpful for when I am in the middle of a hard climb while exercising. I look at the soil and start thinking about the processes that may have occurred to get it to it's current state to distract myself. Recently, while riding, I was distracted by (and was fairly irritated) horse hoof prints on the trail. Many of the riders in the area (both horse and bike) are very respectful of trail conditions post-rain events, so it was pretty shocking to see the damage inflicted on the trail. For a more technical dissection of why activity on the trails too soon after a rain event can be detrimental see Talus' blog post on soil conditions and rain - Playing in the Mud.

Mountain biking in Santa Cruz, CA

But I digress...During the past few years, when noticing soils I also think about what I can share with my students. I have taken photos of all sorts of phenomena related to soils to present to the class. This started me thinking about a "bucket list" of soils that I would love to see in my lifetime. I have modeled my class after my wonderful introductory soils professor, Dr. Mike Singer. Each class he would have "Soil of the Day" and show us a new soil type from around the globe. I have incorporated this into my class as "Soil Order of the Week." One of these soil orders that I would love to see are Gelisols!
Gelisols are new comers to the the soil taxonomy system, only getting their own designation by the USDA NRCS in 1998. The root "gel" is greek for "icy cold", so as you can guess these soils are associated with freezing conditions.  Many soils get very cold in the winter, but these soils have particular characteristics that make them different from those with seasonally cold temperatures. More specifically, they contain a permafrost layer within ~40 inches of the soil surface. Also, these soils often have high amounts of organic matter. The leaves, roots, and other organic materials decompose very slowly due to these cold temperatures. Gelisols can be found commonly in Alaska, northern Canada, and Russia. During the summer, some melting in the upper horizons will occur and areas with these soils will end up becoming bogs/wetlands.

Melting without refreezing can become a permanent and a major issue in terms of engineering issues. Where roads are built over these soils, the translocation of heat from the asphalt surface to the soil can result in higher temperatures and melt the permafrost layer. As these soils tend to have large amounts of organic matter (as opposed to mineral soil a.k.a. dirt...) the increase in soil temperature will consequently increase the microbial activity. The soil microbes will begin decomposing this organic material, which means that it begins to disappear and the surface where the road was built begins to diminish. Without the support of the soil, the road will eventually collapse! 

On the Alaska Highway, thaw subsidence of the permafrost resulted in rapid collapse of the roadbed and surface. The driver of this pickup truck attempted to cross, but the asphalt gave way completely. Later rebuilding included mechanical air drains to prevent heat transfer from the road surface to the underlying permafrost.
Melting of the permafrost is also caused by increasing global temperatures. With melting of permafrost and subsequent decomposition of organic matter, more carbon dioxide is being released into the atmosphere. An increase in carbon dioxide, a greenhouse gas, leads to further increased atmospheric and soil temperatures essentially creating a feedback loop. The short-wave radiation from the sun that would normally be reflected off the surface of the earth as long-wave radiation ends up getting "trapped" by these greenhouse gases. The greenhouse effect is beneficial to a certain extent. It's the reason why we can exist on earth! However, too much of good thing can be harmful. For more on the greenhouse effect please see What is the Greenhouse Effect? by the American Chemical Society.
Well, I don't want to leave you totally depressed. However, knowing these tidbits of information can help you be informed when it comes to soils, climate, and our planet in general. Next time you go out in the world whether it be by on foot, in a car, or even by boat, what do you notice about the soils around you? Is there anything in particular that catches your eye? With gelisols, their unusual permafrost layer definitely intrigued me. In 2010, a gelisol was discovered in the Sierra Nevada Mountains in California. So maybe I won't have to travel as far as Alaska to see this amazing soil. It's possible on my next local adventure I may encounter a gelisol or two...

Backpacking in the Sierras