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Posts Tagged ‘Ireland’

Mark another one off the books. As of tomorrow I will be leaving Donegal for the year after finishing up the sampling in the Blue Stacks. It has been a hot past few days. Maybe not in DC terms, but definitely in Irish terms. The added heat, long hike, and heavier granite samples led to some exhausting days in the field. For that reason, when I finished up today I paid homage to Francis M. Synge, a Irish glacial geologist who would celebrate finishing a field site by going for a swim in the tarn. The water sure was cold, but felt mighty fine after the hot day of sledge swinging.

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With two or three more areas left to sample the equipment is starting to show wear and tear. I already broke one carbide-tipped chisel with Alan, and the replacement one without the carbide tip is rounding off quickly. It has already lost every bit of it’s padding that made it appealing in the first place. My work gloves are starting to get holes in the fingers, and my field pants are starting to develop holes where I won’t mention.

My hands are starting to feel some wear and tear as well. Nothing bad, just sore from all the errant hammer swings that catch a knuckle or thumb.

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I got the good word that the first batch of samples has already arrived in Oregon, and the next batch was placed in the mail today. It will be nice having them waiting for me when I return in a couple of weeks. I’ll probably take a moment to breath, and then get right to processing them in the lab. That’s the plan anyways.

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It has been an eventful past few days. Most importantly, this last Tuesday saw the arrival of my good friend, and geology partner, Alan D. Pitts, on loan from University de Camerino in Italy. He had finished up another year of field camp instruction with the James Madison University group in Connemara and stuck around to help me out. We decided to work on the cirque just north of Killarey Harbor in Mayo that we had visited when we were here two years ago. Working there also gave us the opportunity to visit with some local friends I had not seen in awhile. There may have also been some dancing involved, but I won’t get into that.

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What we aimed to be a one-day sample job slowly turned into three. I am lying here now after a long day of sampling writing this up and compiling all of the data we have gathered. The good news is that we were able to assemble pretty good coverage of samples that will hopefully help constrain the interpretation of this cirque’s glacial history.

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Most of our days were spent sampling, recording, and discussing. It was very helpful to have Alan around, not only for the extra muscle but also for his geologic know-how and familiarity with the site. As of now we have roughly two or three working hypotheses for this quite complicated cirque. This area may be one of the least straightforward areas I visit this year. What excites me about this site though is that the dates we get back from our samples will almost certainly confirm one of our hypotheses.

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With the Sruhauncullinmore site completed that leaves four more to go. Unfortunately tomorrow we drive back to Dublin so Alan can catch his plane home. Afterwards I will be solo once again. I am thinking I will head north this time to Donegal, and maybe work my way south.

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Yesterday we got into the field and explored up within the glacial valleys of the MacGillycuddy’s Reeks. What initially started as a reconnaissance/site scouting mission soon turned into me collecting my first samples as we encountered a few boulders that were too good to pass up. As we kept moving further and further into the valley we kept finding more moraines. Eventually the weather turned sour and we had to call it a day. The high winds and horizontal rain were a little too much to tolerate on the second day.

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The weather was worse today, especially up on the mountains, so we used this as an opportunity to drive out to the Dingle Peninsula and site scout some cirques. The peninsula is a beautiful area of Ireland with great views of the Atlantic Ocean from high cliffs. After driving the perimeter, we drove up and over Conor Pass to search out the cirques. Unfortunately the cloud cover wasn’t cooperating and it was difficult to determine if there were moraines or even boulders worth sampling. Fortunately we did find a cirque with an ice fall and the possibility of multiple sampling sites. It is also historically significant as the site were the ice ages were first recognized in Ireland.

Here is a nice view on the peninsula.

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After two over night flights, visiting family in NYC, and more money than I like in baggage fees, I arrived in Ireland this morning. I was picked up at Shannon Airport by my adviser Peter and his field experienced wife, Jorie. Immediately we set out from the airport for Killarney in County Kerry with the goals of staying awake and prepping for the field work. We grabbed a few supplies in town including this Discovery Series topographic map of Ireland.

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After getting settled and grabbing some dinner we drove out to eyeball tomorrow’s field site, the MacGillycuddy’s Reeks, in person. Having spent a significant amount of time scouting this site through Google Earth it was an impressive and exciting experience to see just how massive these features really are. In the handful of minutes we were there we already started putting together a game plan and finding areas to sample. It’s looking like this will be a good field site. Hopefully the weather cooperates and we stay dry this week.

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In just over a week I will be boarding a plane for Ireland. This will mark the start of the first of two field seasons for my graduate research involving surface exposure dating of cirque moraines. The plan for this season is to focus on western Irish mountain ranges found in the counties Kerry, Galway, and Mayo including the MacGillycuddy Reeks and the Nephin Beg range. 

Sample collection will involve chiseling off top portions of glacial erratics found along moraine crests, and hauling them back down the mountainside to the vehicle. My understanding is that it will be a bit of a workout. Here is a picture of a few of the tools I will be bringing with me.

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Most of these have already experienced one field season in Antarctica, so I hope they are still up for the task.

I am sure this will provide plenty of storytelling and picture sharing opportunities, and I plan on doing just that through this blog. Hopefully the hostels will be wi-fi friendly. If not, there’s a good chance I could find myself in a coffee shop or two along the way.

Please check back, and I’ll keep the updates coming.

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Not so recently an article was sent to me that discusses how in areas of Sweden the relative sea level is falling and land bridges that did not exist within the last century are starting to appear. For some this could seem as counterintuitive with what is known about rising eustatic sea level caused by climate change. But, the process behind this relative falling sea level is simply isostatic rebound from the Last Glacial Maximum.

During the LGM, the massive Eurasian Ice Sheet depressed the land, and since deglaciation it has been recovering from that depression. What is happening specifically is that the rate of Swedish rebound is higher than the rate of sea level rise.

The process of isostatic rebound is becoming a concept of large importance for me to work with in a couple of ways. One of the ways we can reconstruct the glacial history of a region is by looking into the relative sea level changes experienced there. Using those changes along with an understanding of the global sea level can suggest the presence or lack of overlying ice sheets.

In a 2007 paper, Marshall McCabe et al discuss the relative sea level changes in northeast Ireland experienced after the LGM and up to the Younger Dryas. By using stratigraphic relationships between dated beach deposits and glacial diamictites, McCabe reconstructed a relative sea level curve for the region.

From McCabe et al 2007

At a Kilkeel outcrop (point 2 in the figure), beach notches are found 30 m above current sea level and are infilled with glaciomarine muds. This suggests that at the time of formation of the notches the coastline of Ireland was isostatically depressed 30 meters. Considering that eustatic sea level was 130 m below current during the LGM means the coastline was depressed ~160 m below present. Deglaciation is suggested by a subsequent fall in relative sea level as the unburdened coastline experienced uplift.

Another aspect of isostatic uplift that I have to consider has to do with the surface exposure dating I will use, and is a topic I have discussed at length with fellow students. Glossing over a whole bunch of details, to get as accurate of a date as possible we have to consider not just how long a particular sample was exposed to cosmogenic rays, but also at what altitude the sample was at while being exposed. Objects at higher altitudes will be exposed to more cosmogenic rays than those at lower altitudes. This comes into play where a glacial erratic may be deposited on a moraine that was 160 m below its current altitude during the LGM. Depending on what altitude the erratic was at would effect the calculated age of exposure. Do we use the current altitude in our calculations or the depressed altitude? Or do we compensate for the uplift by trying to adjust the increasing exposure with uplift? If so, do we assume a linear uplift, or the rebound curve that shows high initial rates followed by lower rates of uplift? Also, how significant of a difference does it make on the final calculation?

I understand that these are a lot of questions to consider, and ones I am sure I will have to tackle in the coming months. The truth is I welcome the discussion that will come, and if anyone reading this has thoughts or suggestions please feel free to chime in on the comments section.

 

McCabe, a. M., Cooper, J. a. G., & Kelley, J. T. (2007). Relative sea-level changes from NE Ireland during the last glacial termination. Journal of the Geological Society, 164(5), 1059–1063.

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This past summer I found cirques to be one of the more visually outstanding and impressive features. The appealing visual aspect may have to do with the propensity of cirques to be found in mountaintop scenery, or maybe even their juxtaposition of inward depressions next to jagged peaks. At the same time, it is hard to see one and not consider their geologic significance.

As with many of my recent adventures and subsequent blog entries, my first known encounter with this particular glacial feature was in Ireland along the western coast, though not the coastline itself. Our glacial project found us in the middle of Big Daddy Cirque near the waters of Doo Lough in county Clare; a beautiful piece of countryside with an unfortunate and sad history. The magnitude of the location resonated with me enough so that I found myself actively searching them out along the hike through the Alps, where there were plenty more to take in.

Like I mentioned above, cirques are glacial features found in alpine settings and often near the mountaintop itself. The feature is an eroded out, bowl-shaped area that was the birthplace of an alpine glacier. As moisture travels over the mountain, if cold enough, snow will collect on the more shaded side and sit. As long as more snow accumulates than melts it begins to compact from the pressure forming into ice, and eventually a glacier. Cirque glaciers are constrained in their boundaries which are defined or restricted by the topography. Therefore as the snow collects and compresses the ice pushes back into the mountain creating an amphitheater type feature. Below is a picture of Big Daddy Cirque taken from the lip of the cirque, and another taken from afar.


In the close up photo the curved walls and flat bottom are apparent from where the rounded glacier sat. In the second photo the scope of the feature is revealed and the overall “bowl” shape is more noticeable. Here is an annotated version of the second photo highlighting the lip and top of the cirque. The blue X marks where the first photo was taken, and the red arrow points “inward” towards the center of the cirque.

Cirques were formed as erosional features as the alpine glacier propagated from the center and dug into the mountainside carving out a rounded surface. The conventional thought was that movement of the glacier was from sliding and rotating in the recessional surfaces of the mountain. But, in a paper published in the October 2010 issue of the American Journal of Science, a team of glaciologists suggest that internal shear of the ice is the driving factor behind propagation, and the rotation is also a result of internal deformation. Basal sliding from base meltwater does occur, though, only at a minimum.

To help visualize the process I have annotated some pictures of a cirque I found in the Alps. Here is the cirque as it exists today:

The annotations are a little hard to see so feel free to follow the link to a larger image. Thanks.

Moisture travels over the mountain and collects as snow and ice on the shaded side of the mountain.

As long as the rate of accumulation of snow is greater than the rate at which it melts (ablation zone) then the snow will compact under pressure to form a glacier. The glacier erodes away at the mountain creating the amphitheater shape depression.

Deviatoric stress from pressure is the driving force that propagates the glacier further down the slope out from the center, and the glacier continues to erode the landscape.

While cirques are significant for being the starting point of glacial expansion, they are just as significant for being the last gasp of glacial retreat. Just as the glacier propagates outward from the cirque, as the glacier melts it regresses back to the same spot before melting away. Evidence for this retreat is seen in features like recessional moraines. So, looking at the cirques above we can appreciate the handy work of a glacier that used to be.

References:
Sanders, J.W., Cuffey, K.M., MacGregor, K.R., Kavanaugh, J.L., and Dow, C.F., 2010. Dynamics of an Alpine Cirque Glacier. American Journal of Science, v. 310, pp. 753 – 773.


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