Disclaimer: I'm not making any political or religious comment about the situation in Egypt, I'm simply amused by the combination of satire & geology, and I hope readers are as well
January 28, 2011
The strata of Egypt??
I don't think I've ever seen a satirical use of a stratigraphic cross-section before, but last night I caught the Daily Show and this funny block diagram (Stewart remarked about how it was a great untapped reservoir):
There can be a lot of comedy in geology if one looks for it, notwithstanding all the unintentionally funny misspellings of terminology.
Disclaimer: I'm not making any political or religious comment about the situation in Egypt, I'm simply amused by the combination of satire & geology, and I hope readers are as well
Disclaimer: I'm not making any political or religious comment about the situation in Egypt, I'm simply amused by the combination of satire & geology, and I hope readers are as well
January 25, 2011
Looking through the archives: My poster on the Geology of the Southern Appalachians
This was the first poster I ever did for a geology-related course. At the time I thought the idea was a bit silly, but in retrospect and with more exposure to the world of geologic academia, I realize it is an essential tool in showcasing research. Nowadays my apartment walls are teeming with geomaps, cratonic maps, deep time diagrams, rocks & minerals picture tables, etc...
Interestingly I made my first draft of this poster by staying up at nights in New Mexico hotels during a geology-heavy vacation there, and thus I started fiddling with making one for the state. Saved me some time for a later course. If you want to take a look, click on the above thumbnail for the poster, and download the poster file (format is Powerpoint .ppt). References are available here
January 22, 2011
On the Geology & Topography of Cornwall
Recently completed a spatial analysis of Cornwall. While scrutinizing the land, naturally my mind wanders towards investigating the county's geology. What I found was quite a unique hodgepodge of different mechanisms & features which make Cornwall quite distinct from the other 7 counties in the southwest of England that I have also done analyzes for.
Looking to the interior of Cornwall, which is never greater than 50km across, one notices broad open landscapes broken up occasionally by tors and moors. These are the result of a granite underbelly that interjected pluton masses from a large batholith, formed during the coming together of our last supercontinent Pangaea. The tor/moor uplands contain quite acidic soils fueled by detritus of granite parent material from the plutons, and serve as the gathering point for headwaters of most of Cornwall's rivers. Bodmin Moor is a textbook example of broad radial drainage pattern from a high peak.
To set the stage for Cornwall's geological underpinnings, I have to start back in the Devonian when marine sand was being lain down, preparing for its inevitable lithification and rapid uplift (is there any part of England without Devonian sandstone?). The mechanism to bring it above sea level was the Variscan orogeny of the Permian, northern Europe's part of the formation of Pangaea, with a mobile belt stretching in a northeast trending arc from Portugal - Poland. The orogeny uplifted the sedimentary basins, and also introduced folds & faults into various sedimentary formations throughout Cornwall. One particular fold is visible near the aforementioned town of Bude on the northeast coast, where a picture-perfect chevron fold shows the changing direction of thrusting during the length of the Variscan. The only Precambrian rocks exposed at the surface in Cornwall are scattered remnants of Man of War gneiss wherein Phanerozoic strata eroded to expose them; those are mostly found in the tors and moors of the Cornish uplands.
An ophiolite was also uplifted during the Variscan, but surprisingly its emplacement/obduction upon the southwest tip of Cornwall was not part of the closing & consumption of the Paleotethys ocean. Rather it was already there, dated to the Devonian and coinciding with the subduction of an arm of the Prototethys. This Lizard complex ophiolite, which is discussed further in this post, was named after the Lizard peninsula which serves as the southernmost extreme point of mainland England @ 50°N 5°12'W.
Cornwall truly differs from other county's in England based on what underlies the strata, and that is the Cornubian Batholith. The Cornubian Batholith (using the Roman name for Cornwall) is essentially a discordant granite batholith that has roughly 8 plutonic extensions that have intruded into the upper crust and been exposed via erosion (though some remain submarine). The batholith emplacement has been dated, using typical radiometric techniques, as Permian, thus matching the theorized Variscan orogeny. The mechanism(s) of emplacement/intrusion into the overlying sedimentary strata are still under debate, with different hypotheses for plutonic injection/growth. There is one concerning a typical diapir mechanism, one that favors feeder dykes supplying magma that was kept hot enough via frequent injections into laccolithic or lopolithic structures in which the shape of plutons were controlled by fault geometry, and finally a hypothesis that favors partial melting and branches of lamprophyre dykes as the source of pluton material via access to mantle magma through a network of extensional faults. These various methods are highlighted in the "Geology of southwest Cornwall" website link, which happens to be someones doctoral research into 'The Tectonics of Variscan Magmatism & Mineralisation in South West England'. It goes into extensive detail about the batholith's petrology, mineralogy, etc... Ultimately the complex of plutons intruded into the Devonian - Carboniferous sandstones above, and as one would expect there is plenty of contact metamorphism that produced schists & metasandstones surrounding the fringes of the plutons.
First-hand accounts of geologists examining the tor rocks of the plutons denote that what is visually obvious at first glance is numerous megacrysts and sandstone xenoliths (remember back to early days of first-year earth science for the principle of inclusions and aphanitic - porphyritic - phaneritic - pegmatitic crystal formation). Computer modelling, gravity anomalies (above figure) and density contrasts reveal a total volume for the batholith of 68,000 km3. The overall appearance of the batholith is a tabular body, which is 50-60 km wide at its base, with steep sides, a sloping base (possibly tilted 2-3° further south during post-emplacement movements) and an irregular upper surface that is continually being shaped by denudational forces. Think of it as the area of Cornwall + Devon, but with a depth of sea level - Mt. McKinley.
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| Land's End headland on southwest tip of Cornwall. Resistant sandstone has been shaped by erosion into pillars |
Upon sweeping around the place, I noticed how similar land development was to, well, every other county I've looked at. Towns are few, with farms taking up about 90% of the land, with quarries scattered here and there (you'll find out why further down). Being on the southwest peninsula, Cornwall is exposed to the brunt of the Atlantic's influence, so winds are consistent and the temperature & precipitation regimes, thanks to the Gulf Stream, are mild and broken up only by occasional storms. Headland erosion is a process that has made a home in Cornwall, with the northern coastline getting pounded with more voracity than the south. The geomorphology of the northern coast interchanges between sandy beaches and steep cliffs (High Cliff ~240m face; sandstone cliffs near Bude). Resistant metasandstones at Land's End, morphosed due to contact metamorphism, highlight some of the rugged coastline typical of Cornwall. The southern coastline is more reserved, with more gradual gradients from the interior hills and more fluvial delta deposition. Energy from erosive forces have in past periods focused more on the south, so wave-cut platforms are more prevalent.
Looking to the interior of Cornwall, which is never greater than 50km across, one notices broad open landscapes broken up occasionally by tors and moors. These are the result of a granite underbelly that interjected pluton masses from a large batholith, formed during the coming together of our last supercontinent Pangaea. The tor/moor uplands contain quite acidic soils fueled by detritus of granite parent material from the plutons, and serve as the gathering point for headwaters of most of Cornwall's rivers. Bodmin Moor is a textbook example of broad radial drainage pattern from a high peak.
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| Cornwall surficial geologic units |
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| Chevron folding at Millook Haven, part of the Culm Measures formation |
Cornwall truly differs from other county's in England based on what underlies the strata, and that is the Cornubian Batholith. The Cornubian Batholith (using the Roman name for Cornwall) is essentially a discordant granite batholith that has roughly 8 plutonic extensions that have intruded into the upper crust and been exposed via erosion (though some remain submarine). The batholith emplacement has been dated, using typical radiometric techniques, as Permian, thus matching the theorized Variscan orogeny. The mechanism(s) of emplacement/intrusion into the overlying sedimentary strata are still under debate, with different hypotheses for plutonic injection/growth. There is one concerning a typical diapir mechanism, one that favors feeder dykes supplying magma that was kept hot enough via frequent injections into laccolithic or lopolithic structures in which the shape of plutons were controlled by fault geometry, and finally a hypothesis that favors partial melting and branches of lamprophyre dykes as the source of pluton material via access to mantle magma through a network of extensional faults. These various methods are highlighted in the "Geology of southwest Cornwall" website link, which happens to be someones doctoral research into 'The Tectonics of Variscan Magmatism & Mineralisation in South West England'. It goes into extensive detail about the batholith's petrology, mineralogy, etc... Ultimately the complex of plutons intruded into the Devonian - Carboniferous sandstones above, and as one would expect there is plenty of contact metamorphism that produced schists & metasandstones surrounding the fringes of the plutons.
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| Cornubian batholith granite outcrops. Diagram shows negative gravity anomaly caused by granite plutons having a lower density than surrounding metasandstones & schists + uplift of the terrain |
The batholith has resulted in mineral richness for Cornwall, with mining operations throughout the last century acquiring mineralized Silver, Copper, Lead, Tin, and Zinc, along with quarrying the ammonium-rich granite and kaolinite, that nice soft moldable clay mineral that provides us pottery and loo's. A lot of the mineralization comes from metasomatism processes that allowed elements to coalesce from mass fluid movements.
The icing on the Cornish geology cake has to be the Lizard complex ophiolite, located on the southwest tip of the county. It was obducted onto the protocontinent of Laurasia in the Devonian, and sheared by thrust & extensional faults, especially during the Variscan orogeny. It's true that the vast majority of ophiolites are rarely an intact specimen from META/IGNY basement - pillow basalts on top, but amazingly the Lizard does not stretch its oceanic crustal segments over a large area, certainly not compared to the ophiolites I've studied in the southern Appalachians as part of the Alleghenian orogeny.
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| Lizard peninsula in Cornwall. Blue line represents Helford river, a ria that prior to the last ice age was a true river flowing along a normal fault |
The current composition of the ophiolite fragments are serpentinite, amphibolite, and schist facies, respectively representing the harzburgite basement, the gabbro magma chamber, and the sheeted dykes. There's even some high grade gneiss found in the Goonhilly Downs, which is derived from the Man of War gneiss mentioned previously. Pillow basalts are still pillow basalts for the most part, though they were poorly preserved in this instance. Topographically the peninsula is mostly a raised platform between 50 - 100m, with the Goonhilly Downs satellite dish network (a future space science center) at the highest part. The serpentinite material, along with poor drainage, has given rise to a heathland where dwarf shrubs dominate due to the basic soils (ex. Cornish heath).
To conclude this post, I would have to say that observing Cornwall has been a treat. It wasn't immediately unique compared to the rest of southwest England, but after several minutes in I started noticing the big differences, and along with Devon it makes up a distinct geological history from Devonian to the present. A granite backbone, tough sandstone cliffs, and an ophiolite to boot. Makes it a treat to write a lengthy post about the county ... as a way to have a deeper understanding of the place I'm analyzing and to just plain learn more geographical geology. I invite anyone also interested in European history to look into Cornwall's Celtic heritage, and how the Arthurian legends are tied to the place. Those cognizant will certainly know of Tintagel Castle.
Additional Info:
Whilst doing some work involving the European Soils Database, I distinctly noted the properties of Cornwall's soils. Looking at the parent material, slate and metasandstones are prevalent for the majority non-moor expanses, whereas acidic soils from the granite plutons make up most of the rest; patchy spots of boulder clay are the only unfeasible spots for agricultural activity. Very thin layers of loess are widespread on the Lizard peninsula. When compared to the rest of the country, Cornwall has quite a shallow depth to rock + a medium-strong erodibility class. Since uplifted sedimentary basins make up the majority of Cornwall's surficial geology, the eroded sandy overburden makes for decent aquifer material, allowing for a high topsoil & subsoil water capacity that is easily available for crops and other plants to soak up.
To conclude this post, I would have to say that observing Cornwall has been a treat. It wasn't immediately unique compared to the rest of southwest England, but after several minutes in I started noticing the big differences, and along with Devon it makes up a distinct geological history from Devonian to the present. A granite backbone, tough sandstone cliffs, and an ophiolite to boot. Makes it a treat to write a lengthy post about the county ... as a way to have a deeper understanding of the place I'm analyzing and to just plain learn more geographical geology. I invite anyone also interested in European history to look into Cornwall's Celtic heritage, and how the Arthurian legends are tied to the place. Those cognizant will certainly know of Tintagel Castle.
Additional Info:
- The Geology of southwest Cornwall
- Dangerfield & Hawkes - Variscan granites of southwest England
- Thermochronology of the Cornubian batholith in southwest England: Implications for pluton emplacement and protracted hydrothermal mineralization
- The Lizard complex as an ophiolite
- Slow-spreading ridge-axis tectonics: evidence from the Lizard complex
- EU Soils
January 17, 2011
"Indians!"
What does the geo-minded individual focus on in a movie, especially one with beautiful scenery ripe with geologic history? When I was a younger man, I wouldn't give much thought to what I was looking at and how it's possible for landscapes to be like that, and in any case the action and story would (or at least should) keep me enthralled. But after spending a few years immersed in various topics and sundries of geology, I started catching myself paying attention to the places rather than the people, especially when showing open country. Certain flicks have DP's who photograph and Editor's who showcase the filming locations in such breathtaking sweeping visuals that I cannot help but let the mind wander off from whats going on screen and towards the realm of the geologic.
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| What part of this scene are you looking at? (photo courtesy Universal Pictures) |
Sometimes I'll even buy a DVD of a mediocre movie simply because it had plenty of outdoor visuals of a spectacular natural wonder or formation/group (ie. The Canyon) or what-have-you. Plus I'm always checking the filming locations on IMDB as a kind of geography jeopardy with my sweetheart. Then its off to Google Earth to match the cinematography with the real place (recently spotted where Tom Hank's island in Cast Away is located).
One thing I wish movies of this new decade would focus on is a return to the Western genre. Every current and inspiring geologist should be a fan of Western's but for their displays of the untouched parts of the American West. Now off to watch The Missing.....for the Valles Caldera & the few seconds they show a rhyolite lava dome in the valley.
January 14, 2011
Papers I'm reading: Expansion of Juneau Icefield glaciers in late Holocene
Being a poor undergraduate student, I tend to savagely bite my pocketbook whenever I plunk down for some new textbooks or access to academic papers. Amazon has become a great source for affordable books, but when it comes to papers, the search for freely available ones is like a search for lost treasure. Whenever I find one, its like finding the pot of gold at the end of the rainbow. More often these days I am finding free papers, usually from professor recommendations, blogs, and branching out from the Wikipedia hub. I'm not a complete cheapskate – I purchased Anne Jefferson's paper on Hydrology & Topography of Oregon's High Cascades, and reading it actually led me to visit the primary site (Pacific Crest trail to Belknap Crater) when I was last in Oregon.
My geomorphology professor happened to be a glaciologist, who tends to drop off the face of the planet during his ventures to Greenland & Antarctica (he's down in the deepest south now during the window). He sent me word of some freely available papers he authored, and I took a look at his latest paper, dealing with the advance or retreat of glacier tongues in the Juneau icefield during the late Holocene (CE years), and how the chronology of those movements challenge the term "Little Ice Age". I'm wide-eyed when reading these and actually understanding most of what is said (though details of mass spectrometry still confuse me - I need access to one to play around with).
Radiocarbon and dendrochronological dating of glacially overridden stumps and detrital wood indicates that two outlet glaciers of the Juneau Icefield advanced shortly before the ‘Little Ice Age’. Tulsequah Glacier advanced to within 2.4 km of its all-time Holocene limit between ad 865 and ad 940. Llewellyn Glacier, one of the largest glaciers in British Columbia, advanced sometime between ad 300 and ad 500, and reached to within 400 m of its Holocene limit between ad 1035 and ad 1210, well before the climactic, ‘classical’ ‘Little Ice Age’ advances of the past several centuries. Our data show that some glaciers in western North America were extensive and expanding at times when alpine glaciers have, in the past, been assumed to be restricted. The evidence raises questions about how to define the time of the beginning of the ‘Little Ice Age’ and, perhaps more importantly, about the utility of the term.
Llewelyn glacier w/ finger
of Atlin Lake
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| Map of Juneau Icefield, studied glaciers labeled |
Moraines and ice-dammed lakes are utilized to define the geomorphology of the glacially-carved valleys. Dendrochronology and radiocarbon dating of 14Carbon isotope was heavily used (and I do mean heavily), for detrital wood caught in morainal till and diamicton layers. Death of subalpine fir (Abies lasiocarpa) was used to date advances of glacial tongues, bulldozing vegetation along their course.
The Landsat image below highlights a portion of the study area, showing Tulsequah glacier and how exposed land is confined to a constricted valley that is essentially the glacier's foreland. The Tulsequah river flows into the Taku river, which then flows into the sea around the Alaskan panhandle fjords. The 'Rock Ridge' is a till-covered roche moutonnée, from which many samples of stumps were used for 14Carbon dating. This is all viewable on Google Earth; check 58° 38.00'N 133° 33.00'W (Tulsequah & Taku confluence) and move in a NNW direction up valley. The gradient of the valley is a bit below 1%.
The general stratigraphy involves a mixture of glaciolacustrine sand & gravel overlain by diamicton and glacial till, which pressed into fractures of the lower lacustrine layer, forming clastic dykes. A thin veneer of modern glaciofluvial gravel-grading-to-silt is the icing on the cake in some parts of the river valley.
I generally get 3 things out of a peer-reviewed paper:
- A new term learned; in this case it was Ecesis
- A new question raised; in this case How does this evidence correlate with accumulation/ablation for alpine glaciers in the same time period for the Coast mountain belt?
- A new realization; in this case clastic dykes → glaciotectonic fractures/deformation are more important in the field studying of glaciers than I thought (maybe because this very professor downplayed them)
Additional Info:January 10, 2011
Neptunist vs Plutonist
Brian Romans over @ Clastic Detritus was recently selected as a finalist for science blogging due to his post about Rapid Canyon Formation and Uniformitarianism. The Uniformitarianism vs Catastrophism debate is likely familiar to every geo-blogger, or quite frankly anyone who has taken a historical geology course or read about the 19th century debate. The argument seems quaint and anachronistic these days, but the human condition seems to often unnecessarily dig up old black & white positions on topics that have already moved light-years beyond. I guess cherry-picking ignorance doesn't seem to have a retirement age. This is not to say that we should ignore old debates, as understanding the evolution of the school of geologic thought serves as an important reminder about how methodologies and discussions should and should not be approached.
One item that popped into mind when thinking about Uniformitarianism vs Catastrophism was the preceding debate over the origin of the Earth's crust and its variations of bedrock (IG, SED, META). Neptunism vs Plutonism was a classic geologic debate that showed the value of field work and how direct evidence gathered from it strengthens a hypothesis. Geology and its various branches literally just don't work without field study.
The Neptunist view of the origin of the solid Earth was spearheaded by Abraham Gottlob Werner, a German geologist of the 18th century who instructed at the Freiburg Mining Academy in Saxony. He was considered a competent mineralogist by his peers and students, and his scheme for identifying minerals and ores was pervasive throughout the industry in Europe. Central to Werner's own work was his interpretation of the geologic history of the Earth. His treatise outlined how all rocks of the Earth's crust were mostly of marine origin, deposited or precipitated from a worldwide ocean that once enveloped the entire planet. Sounds like that awful Kevin Costner movie. Certainly many sedimentary rocks are of marine origin, but others are definitely not formed in any way by water. Anyways, Werner's envisioned planetary ocean was placed in Deep Time's Archean (which wasn't yet conceived, but for simplicity's sake lets say Werner placed it in the oldest eon) and characterized as a hot, scalding primordial soup that was saturated with all the dissolved minerals needed to form the basement rocks (Urgebirge), essentially the igneous & metamorphic cores of mountain ranges, cratons, and platform bases.
Werner's interpretation continued into the next phase with the onset of subsidence and cooling of the old ocean. This phase was marked by the deposition of consolidated, stratified, and fossiliferous sedimentary strata that was structurally deformed in many places. The fossils, he said, proved the planet had become suitable for life, and indeed this may have been an early explanation for the Cambrian explosion of the early Paleozoic era. Above these rocks layers was what Werner called Flotzgebirge, a term used to explain formations and groups of sandstones, shales, coal beds, limestones, and even basalt. But therein lies the problem we can all identify, using our 200 years of compounded knowledge and in situ studies.
As the 18th century drew to a close, criticism of Neptunism strengthened with visible and indisputable field evidence for the counterargument of Plutonism. Geologists, especially ones investigating volcanic complexes in France's Massif Central (Nicolas Desmarest, Alexander von Humboldt, Rudolph Eric Raspe), were able to clearly demonstrate volcanic origins for basaltic layers and various features such as cross-cutting dykes, sills, tephra layers and structures (*wink* like Pumice Castle *wink*). Geologists who conducted these field studies formulated an opposing view, and came to be the Plutonists. According to the Plutonists, fire was the key to the origin of igneous rocks such as basalt, not precipitated minerals from a marine environment. James Hutton, considered one of the fathers of early geology, was an advocate for Plutonism who stated that classical igneous rocks such as basalt and granite “formed in the bowels of the Earth from melted matter poured into rents and openings in the strata”. Hutton's Uniformitarianism concept also espoused how the agents of deposition and erosion at work in the present have been working since the beginning of the Earth. The Neptunist vs Plutonist debate thus became amplified in the later Uniformitarianism vs Catastrophism debate, with many of the same hypotheses being refined and carried over. I wonder how much the spirit of those old arguments carried into the Geosyncline vs Plate Tectonic debate.
Debate is good for the evolution of a scientific discipline, and though today's debates in geological academia are of a different flavor than the one I've just focused this post on, they are just as important in furthering our understanding of the spheres of our natural world, an understanding that I hope never comes to a completion. If anyone wants to check out some quoted material from early Plutonists, look no further than this page which has explanations of fractionation & igneous differentiation by English geologist George Poulett Scroupe.
One item that popped into mind when thinking about Uniformitarianism vs Catastrophism was the preceding debate over the origin of the Earth's crust and its variations of bedrock (IG, SED, META). Neptunism vs Plutonism was a classic geologic debate that showed the value of field work and how direct evidence gathered from it strengthens a hypothesis. Geology and its various branches literally just don't work without field study.
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| Abraham Gottlob Werner circa 1800 |
So although initially received with great interest and enthusiasm, Werner's ideas soon drew criticism for failing not only to properly explain many features of plutonic & volcanic origin (see below), but what had become of the immense volume of water that once covered the Earth to a depth so great that all continents were totally inundated. The amount locked in continental & alpine glaciers in the late 1700's was not sufficient explanation, given knowledge of the cryosphere in the 18th century, and the topography of the ocean floor was barely mapped (it wouldn't explain it anyways). Neptunism had to pooh-pooh anything to do with volcanism, and some of the ideas bandied about were absurd even for the day. I once read that volcanoes were vents for the expulsion of burning plant matter (coal) from within the Earth; essentially they were labeled by Neptunists as cone-shaped barbecues.
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| Various volcanic features and forms, most of which were unexplained or dismissed by Neptunists |
Debate is good for the evolution of a scientific discipline, and though today's debates in geological academia are of a different flavor than the one I've just focused this post on, they are just as important in furthering our understanding of the spheres of our natural world, an understanding that I hope never comes to a completion. If anyone wants to check out some quoted material from early Plutonists, look no further than this page which has explanations of fractionation & igneous differentiation by English geologist George Poulett Scroupe.
January 6, 2011
It's Cold and Loud Up There
My country's weather network occasionally shows vignettes about weather trivia, and one of them furrowed the brow of my sweetheart when she heard it, and truth be told it threw me off a bit as well.
It might sound counter-intuitive, but if sound travels faster it does not also travel further. Within warmer air masses, molecules are moving (vibrating) more rapidly, and thus the propagation of sound waves, which move via molecular collision, is quicker. However, as the molecules of air in a warmer air mass are further apart due to expansion, attenuation of sound waves will occur, and thus the intensity (decibel) of the sound will diminish compared to a colder air mass. Essentially warmer air is "stiffer", not as “elastic” as colder air due to the molecules moving around with more energy.
The coldest temperature ever recorded in Canada was on February 2, 1947 in Snag, Yukon. The air temperature was -63°C. The air was so cold that meteorologists in the area could hear voices from 6 kilometers away.This lead to questions of whether sound waves can travel further in cold or warm air masses, all else being equal. So I, with my limited physics and more thorough atmospheric science knowledge take a stab at the inquiry.
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| Google Earth snapshot of Snag area (62° 23.954'N 140° 22.302'W) Nearest significant hills are 15+km north |
Density is the key for the propagation of sound, and as we all know a cold air mass is denser, with more tightly packed molecules. Under those conditions, attenuation is not as pronounced, and sound waves collide molecule-molecule with ease. But these are simply the basic conditions for sound in the atmosphere, and a Chicago meteorologist explains the key factor best:
The most important factor, though, is the great difference in the thermal structure of the lower atmosphere when it is cold versus when it is hot. When air temperatures change along the path that sound waves are traveling, the waves always bend toward the colder air. In bitterly cold arctic air masses, the coldest temperatures are at the ground with higher temperatures above; sound waves do not disburse upward readily. On hot days, it's just the opposite: It's hottest at the ground and cooler above; sound waves bend up and away.
Certainly to get a -63°C temperature requires a bitterly cold arctic air mass, and early February is deep within winter, where the snow cover is widespread and the positive feedback of constant reflective albedo has had plenty of time to cool down the region. The nearest major town with historical records from Environment Canada is Burwash Landing, and Burwash shows a February daily minimum average of -25°C, with an extreme of -55°C recorded in 1968. This highlights an extreme diurnal temperature range due to continentality. The Gulf of Alaska is ~300km away, but High pressure Arctic anticyclones (cA) sweeping down from the Beaufort Sea (which is equivalent to a white landmass) ~800km away, prevail over any weak westerlies from the northeast Pacific. The February polar jet stream is far below Snag.
I hope this clears up the same question anyone else might have about air temperature and how sound carries. Inevitably other factors, such as wind direction/speed, topography, and humidity come into play and add complexity. Back on that mighty cold day, the meteorologists also made mention that they could hear their breath freezing just after exhaling. Be careful not to shout in -63°C, or you might break your foot.
I hope this clears up the same question anyone else might have about air temperature and how sound carries. Inevitably other factors, such as wind direction/speed, topography, and humidity come into play and add complexity. Back on that mighty cold day, the meteorologists also made mention that they could hear their breath freezing just after exhaling. Be careful not to shout in -63°C, or you might break your foot.
January 3, 2011
On the Geology & Topography of Herefs
Last summer my experience at university took an interesting turn, as I was recommended to a couple of professors to be taken on as a research assistant. The work primarily involves GIS mapping with ArcGIS. I jumped at the opportunity to get involved in academic research in the realm of geography, and the flexibility it offered fit around my existing work and studies quite well. I'm a bit of a workaholic, and not a procrastinator (does that word have an antonym?), and I think that came as a surprise to my new bosses.
One of my bosses doctoral research involves various counties of England and their historical land ownership issues. The work that is thrown my way generally involves spatial analysis of locations and distances within these counties, and I've relished learning the specific geography of each. So far focus has been on the Southwest, but the most recent county I've examined is Herefordshire in the west midlands. I use Google Earth to gather location elevation data, and when perusing the county, I got a sense of its topography and land use. But that's not where a geonut would stop inquiring; we need to know why the topography is the way it is.
Many people (and by that I mean my narrow assumption) when they think of the countryside in England picture rolling green hills and a preponderance of farm plots, broken up occasionally by a Sanford Gloucestershire-type town. Herefordshire turned out to be pretty much that way, with a few breaks in the stereotype.
The Bedrock geology of Hereford is dominated by Devonian (416-360 Ma) Old Red Sandstone, a huge sedimentary rock series formed from the erosion & deposition of the ancient Caledonian mountains, which formed when Laurentia (North America) and Avalonia (British Isles + Northeast USA) and Baltica (Scandinavia + Eastern Europe) all collided together, forcing up an imposing mountain range. Over millions of years the Caledonians eroded, and deposited in basins at shoreline margins and across broad tropical plains (England was around the equator for much of the Paleozoic) was the eventual mudstone/sandstone material that would lithify into the ORS. Looking at the figure to the right, a lesser portion of Herefs bedrock is Silurian (444 - 416 Ma) limestones, sandstones and shales, mostly in the northwest & southeast. This Silurian system of sedimentary facies contains the greatest abundance of fossils in Herefs, with brachiopods, trilobites, and the more elusive graptolites. If one were to dissect the underlying strata, one would find an interweave of shales, conglomerates, mudstones, etc....basically a sedimentary rockcake, albeit slanted, slightly deformed, and with a few coal chips.
When I was perusing the southern half of Herefordshire, the most atypical feature that popped out is the River Wye gorge, and the community of Symond's Yat nestled around a bend in it. Here the river cuts a defile in Carboniferous limestone, exposing beautiful cliff faces, dissolved caverns that yielded fossils of deer, mammoth, and rhino analogues. All those features made the area appealing for tourism. Furthermore, the defile's profile reminded me of the Delaware Water Gap in the northeast US, mainly because the first geoposter I ever made had a section about the water gap. They have different geomorphological origins, but there is a resemblance in terms of limestone structure and general topography.
One of my bosses doctoral research involves various counties of England and their historical land ownership issues. The work that is thrown my way generally involves spatial analysis of locations and distances within these counties, and I've relished learning the specific geography of each. So far focus has been on the Southwest, but the most recent county I've examined is Herefordshire in the west midlands. I use Google Earth to gather location elevation data, and when perusing the county, I got a sense of its topography and land use. But that's not where a geonut would stop inquiring; we need to know why the topography is the way it is.
Many people (and by that I mean my narrow assumption) when they think of the countryside in England picture rolling green hills and a preponderance of farm plots, broken up occasionally by a Sanford Gloucestershire-type town. Herefordshire turned out to be pretty much that way, with a few breaks in the stereotype.
There are some unique igneous and metamorphic formations that protrude the landscape. Herefs portion of the Malvern Hills to the southeast are composed of Cambrian quartzite, and so are a few low-relief hills just outside Brampton Bryan, though it would be hard to view them unfettered due to fence-fence agricultural development. Quaternary glacial activity during the Pleistocene brought the bulldozing force of glaciers down to the county, frequently smoothing out and rounding the landscape during advances & retreats, and thus till mantles a fair number of the hills and broad uplands. Glacial erratics were left behind on top of some taller hill groups such as Hanter Hill and Stanner Rocks, both plutons. Chronological evidence of the furthest extent of glacial tongues ends 20 Ka, spreading into what is now the courses of the River's Lugg and Wye.
When I was perusing the southern half of Herefordshire, the most atypical feature that popped out is the River Wye gorge, and the community of Symond's Yat nestled around a bend in it. Here the river cuts a defile in Carboniferous limestone, exposing beautiful cliff faces, dissolved caverns that yielded fossils of deer, mammoth, and rhino analogues. All those features made the area appealing for tourism. Furthermore, the defile's profile reminded me of the Delaware Water Gap in the northeast US, mainly because the first geoposter I ever made had a section about the water gap. They have different geomorphological origins, but there is a resemblance in terms of limestone structure and general topography.
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| River Wye in southern Herefs (left) Delaware River in eastern Pennsylvania (right) |
It would be a disservice to not mention the characteristics of Herefordshire's soil, which is given a red coloration by weathered Old Red Sandstone particles, making the pedon profile easily identifiable. The soil itself is primarily clay and/or marl. Five minutes on Google Earth in the county shows its multitude of farmland, and every type of use that the English are known for is found in Herefs (cattle, sheep, horse, hops, wheat, barley, turnips, fruit). Pear and Apple orchards dominate cultivated land in the county, ranking only second next to Devon in output; not surprising given Devon's larger area plus its portion of ORS. Man's love of drink means that all that fruit inevitably led to some local brews of cider becoming popular.
Herefordshire is definitive English countryside, and was part of the stomping grounds for the founding minds of geology. Indeed any keen geologist will recognize the significance of the old British tribes Silures & Ordovices and their proximity to the West midlands. Any input from locals of the region is particularly welcome. Next I might look into Devon, as it was the first county I did in-depth spatial analysis for, plus I have enjoyed a few of Dame Agatha Christie's novels set within it.
Additional Info:
- Natural England - Herefordshire
- On the Passage-beds from the Upper Silurian Rocks into the Lower Old Red Sandstone, at Ledbury, Herefordshire
January 1, 2011
The Pawn's First Move
My first post on my new blog, and I guess introduction and purpose are in order.
As a geography/geology undergraduate that has completed his first two years, I feel confident (enough) in my gathered knowledge coupled with a bit of experience with the tools of the trade to start expressing myself more in written form. I hope the blog will not only tune me more towards consistent writing on earth science subject matters and experiences, but also act as a kind of archive of interesting topics I have come across in course studies, field journeys, scholarly papers, publications, and other earth science activities.
Indeed I wish I could continue endlessly taking courses, perpetually learning knew things about every sphere of the earth system, but more and more I find that intermixed with studies is practical application, be it my GIS work for professors, or volunteer work for environmental agencies, or personal exploration of unique geological sites in my neck of the woods.
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| The Pumice Castle at Crater Lake ©Robert Mutch |
Pumice Castle itself is a result of its material toughness and foundation standing tall while deposits and lava flows around it eroded and fell into Crater Lake. Mazama is a composite volcano, its layers alternating between air fall deposits of ash/lapilli and lava flows of a basic to andestic/rhyolitic nature. One such layer of air fall was composed primarily of violently erupted pumice, that when deposited upon the flanks of Mazama was so hot that fragments welded together, and formed a lens roughly 50-60m thick. That pumice layer is underlain by a particularly dense andesite layer from a previous flow, thus providing a strong foundation for the lens to resist erosive forces. The eruption that eventually led to the pumice castle was itself not voluminous, but was fast and explosive in a shorter-than-average time period.
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| NPS diagram at the site |
I recommend Crater Lake as a definite on any North American geo-nut's bucket list, in particular the Rim drive and little side diversions to the Pinnacles (welded fumaroles), Phantom Ship (volcanic plug), Devil's Backbone (andesitic dyke) to name a few. If you're like me, music is your extra companion on fun drives, and my choice for central & south Oregon ended up being Pure Cult. There's nothing quite like driving through the desert scrub on a clear early autumn day whilst She Sells Sanctuary fills the ears.