Archive for the ‘geology’ Category

Permafrost as far South as Georgia during the Last Glacial Maximum

June 4, 2020

This is at least the 7th article I’ve written about Carolina Bays, but I keep coming across new and fascinating studies of these curious geological features. (See: https://markgelbart.wordpress.com/?s=Carolina+Bays ) These oval shaped depressions occur across the Carolinas and Georgia.  Their origins baffle scientists, but the commonly accepted explanation is they are topographical formations resulting from Ice Age wind and water erosion.  (Extraterrestrial explanations can be ruled out because Carolina Bays are of different ages, and there are 500,000 of them compared to just 250 known impact craters on the entire earth’s surface.)  I’ve long understood how wind and water erosion shaped the depressions, but I’ve never been satisfied with explanations for how the land initially subsided.  Some think wind simply blew unconsolidated sediment out of the pits, while I’ve suggested the land subsidence occurred due to peat fires (as occasionally occurs today).  In a new book Chris Swezey of the U.S. Geological Service proposed the initial subsidence of Carolina Bays was caused by discontinuous patches of permafrost that thawed during summers and collapsed.

Formerly, scientists thought permafrost (ground that stays frozen year round) extended as far south as northern Virginia during the Last Glacial Maximum, but Swezey believes there were patchy discontinuous areas of permafrost as far south as Georgia.  Carolina Bays resemble geological features found in southern Alaska today where permafrost is scattered and temporary.  The land swells and collapses and fills with water in oval depressions.  Northern Alaska hosts continuous permanent permafrost.

Millions of Arctic Methane Hotspots Detected by NASA – Global ...

Discontinuous patches of permafrost create lakes in southern Alaska that resemble Carolina Bays located in the upper coastal plain of Georgia and the Carolinas.

Average temperature and sea surface level through 35,000 years related to 1990 level

Temperature graph showing average temperatures and sea level fall during the Last Glacial Maximum. Note the dips at about 27,000 and 24,500 years BP.  This is when discontinuous permafrost could have developed on some Georgia and Carolina soils.

I believe this map is misleading.  It shows the southern extent of the boreal forest zone, but zonal forest types as we know them today didn’t exist then.  From the below referenced paper.

Georgia must have been much colder during Ice Ages than I thought.  Most Carolina Bays formed between 35,000 years BP-15,000 years BP when glaciers expanded to cover Canada and New England.  Some date to earlier stadials of the Wisconsinian Ice Age.  Patchy permafrost in the Carolinas and Georgia likely occurred during especially cold phases of the Ice Age that probably lasted for decades rather than centuries.

Landscapes in Georgia during the LGM must have been varied and interesting.  Wetlands on Carolina Bays likely attracted summer populations of ducks, geese, and swans.  Sand dunes from dried out riverbeds rolled over the land, smothering mixed woodlands of pine, spruce, and oak.  Arid conditions favored grasslands that fed horse, bison, and llama; in turn pursued by giant lions and dire wolves.  Strange as it may seem, caribou and stag-moose ranged into this latitude.  Zonal vegetation as we know it didn’t exist then.  Instead, habitats were patchy and species compositions were dissimilar to those of any existing types of forest.  Local microclimates might favor oak thickets, open spruce woodlands, mature pine forests, grassy meadows, small marshy wetlands, or bare soil.  Less than 100 miles east of the inner coastal plain the climate was markedly warmer.  Land extending into what today is the Atlantic Ocean  hosted more warm weather species of plants and animals because it was closer to warmer ocean currents that moderated coastal climates.  Inland, the boundary between cold and warm climates frequently fluctuated, contributing to the patchy unstable environments unlike those of today.

Reference:

Swezey, Chris

“Quaternary Eolian Sand Dunes and Carolina Bays of the Atlantic Coastal Plain Province, USA”

in

Inland Dunes of North America

edited by Lancaster, Nicholas and Patrick Hesp

Springer Books 2020

 

 

The 57 Year Old Fire in Centralia, Pennsylvania

February 14, 2020

A month after I was born, the town fathers (or maybe they should be known as the village idiots) of Centralia, Pennsylvania thought it would be a good idea to burn the county landfill.  This garbage dump was located next to a coal strip mine in operation since 1935.  The fire ignited an underground coal seam, and it is still burning 57 years later.  3 major attempts to extinguish the fire failed.  Authorities estimate the fire will keep burning for another 250 years, and it will continue to release mercury, sulfur dioxide, nitrogen oxides, particulates, heavy metals, carbon monoxide, and carbon dioxide–all the poisons found in coal.  Heat from the underground fire buckles streets and kills trees.

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Location of Centralia, Pennsylvania.

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Aerial view of Centralia–abandoned homes and dead brown trees.

Centralias PA, route 61

This road is destroyed and smoke sometimes comes through the cracks.  These photos and more can be found within this Business Insider article.  https://www.businessinsider.com/photos-of-abandoned-centralia-pa-2012-5#centralia-is-a-borough-in-the-northeastern-mountains-of-pennsylvania-in-2002-the-us-postal-service-revoked-the-towns-zip-code-17927-1

The town of 1,492 people became quite uninhabitable. During 1984 Congress allocated $42 million to relocate the residents, and the population today is 5.  I tried to determine if wildlife has moved into the area since the people left (like what happened at Chernobyl and the Korean demilitarized zone), but I can’t find anything about it.  For sure this ghost town is an example of the folly of man and in stark contrast to the blog article I wrote last week describing the travels of a man who visited Pennsylvania when it was still mostly a beautiful wilderness.

 

Migrating Carolina Bays

December 21, 2019

Referenced within the study I wrote about last week was another interesting paper that determined some Carolina Bays migrated.  I’ve written about Carolina Bays previously (See: https://markgelbart.wordpress.com/2012/04/30/a-young-carolina-bay-in-north-carolina/ ), but I did not know this.  Carolina Bays are elliptically-shaped depressions found in the Carolinas and Georgia, mostly on the coastal plain.  Wind and water erosion during wildly fluctuating Ice Age climates created these fascinating geological features.  Some are in the process of originating now.  Wind during cold arid climate cycles blew out unconsolidated sediment, and wind-driven water during wetter warmer cycles shaped them.  They vary in size and water content.  Some hold water year round, while others are seasonally dry.  They provide important wetland habitat, especially for amphibians because frog and salamander-eating fish are often absent.  Like so many other natural features, a majority of them have been destroyed by development.  Farmers drain and plough over them.

Scientists studied Herndon Bay in North Carolina.  They used ground penetrating radar to find abandoned rims, also known as lips. The abandoned rims date to 36.7, 29.6, and 27.2 thousand years old, and these dates are associated with climate cycle transitions.  In between these dates Herndon Bay stabilized.  Apparently, Herndon Bay was pushed by wind and moved across the landscape in a process that was too slow for the human eye to follow.  It has stabilized at different locations, and one could say this is a kind of migration across the landscape.

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Ground Penetrating Radar Image from the below reference.  Note the former basins of Herndon Bay.  It has migrated across the landscape.

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Carolina Bay located in Aiken, South Carolina.

Some crackpot scientists think Carolina Bays are craters formed by either comet impact ricochet or a comet striking a glacier, thus causing chunks of ice to fly thousands of miles before landing in southeastern North America.  A single fact debunks this idea–Carolina Bays originated at different times and some are still forming.  They are not the same age, ruling out a single extraterrestrial event.  There are 500,000 Carolina bays, yet less than 200 confirmed impact craters on earth, so this makes it seem highly unlikely as well that they result from multiple impacts.

Reference:

Moore, Christopher & Brooks, Mark & Mallinson, David & Parham, Peter & Ivester, Andrew & K. Feathers, James. (2016).

The Quaternary evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): implications for paleoclimate and oriented lake genesis.

Southeastern Geology. 51. 145-171.

 

Green Sahara Periods

June 29, 2019

I subscribed to The Economist magazine for awhile.  It’s an excellent magazine for news about world affairs.  I’m interested in world affairs, but not to the depth it gets covered in this periodical, and I recently decided not to renew my subscription.  Some of their articles are redundant because they’ll often have 2 articles in  1 issue about the same subject that say the same thing.  Their articles are also far too wordy.  The editors of this magazine need to learn how to be more succinct.  They could probably cut the word count of their articles by 75% and not lose anything in the translation.  In 1 of the last issues I read there was an article (actually 2) about the expansion of the Sahara desert.  The unnamed author of this article assumed the expansion of the Sahara desert was caused by man-made climate change.  His assumption was just plain ignorant.  Astronomically forced insolation can entirely explain the expansion and retraction of the Sahara desert.

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Map comparing vegetation of North Africa during dry and humid climate cycles.  The Sahara desert becomes a lush environment at regular intervals that last for about 6,000 years.  The current natural cycle causes the present day arid conditions.

Scientists have determined  the Sahara desert becomes a lush environment with lightly wooded grasslands, lakes, and rivers at cyclical intervals.  They refer to these times as Green Sahara Periods.  Animal life colonizes the region during Green Sahara Periods, and the environment resembles the Serengeti Plain rather than the desert it is today.  The increase in moisture that transforms the desert into a rich natural community is caused by the 23,000 year variation in the earth’s wobble.  The earth normally spins like a top, and like the child’s toy this spin can wobble.  The wobble leads to a seasonal variation when the earth is closest to the sun (perihelion).  At the point in the cycle when earth is closest to the sun during summer, the amount of solar heat increases in this region.  This differential heating of the atmosphere causes low pressure systems to form over the Sahara, drawing in monsoonal precipitation from the Atlantic Ocean.  10 times more rain falls on the Sahara during humid periods than during present day conditions.  This transforms the region into a much more inhabitable environment.

Evidence of Green Sahara Periods dates to the late Miocene ~9 million years BP.  The last 4 Green Sahara Periods occurred from 6,000-10,000 years BP; 77,000-81,000 years BP; 102,000-108,000 years BP; and 122,000-128,000 years BP.  Notice 1 cycle was skipped.  This was during the Last Glacial Maximum when the earth was particularly arid.  Perhaps, other factors outweighed the 23,000 year cycle.  Scientists have noticed Green Sahara Periods have become less frequent since the mid-Pleistocene.

Evidence for Green Sahara Periods can be found on the land and in the ocean.  Explorers crossing the Sahara desert find dry lake beds and river drainages; and there are many rock paintings depicting scenes rich in wildlife that no longer occur in the region.  Samples of cores drilled from the ocean bottom find fluctuations in dust levels at regular intervals.  Sediment dated to dry periods contains high amounts of dust blown from land in sand storms.  Of course, the amount of sand greatly decreases during humid periods.  The shells of microscopic sea creatures, known as foraminifera, excavated from ocean cores also show isotopic variations that relate to changes in precipitation.

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Rock painting in the Sahara desert depicting giraffes, goats, dogs, and people.  Giraffes no longer occur in this region.

The Green Sahara Periods influenced human history.  The rich environment allowed humans to expand from Africa into Asia across the Levantine gateway.  During desert cycles hunter-gatherers could not cross from 1 continent to the other.  1 study suggests humans may be hastening the expansion of the desert by grazing their livestock on the edges of the desert.  I don’t buy this.  Humans likely play a minor role compared to the natural cycle.  If precipitation increased, the desert would begin retracting, regardless of human activity.

Reference:

Larrasoara, J; A. Roberts, E. Rohlirn

“Dynamics of Green Sahara Periods and their role in Hominim Expansion”

Plos One 2013

Late Pleistocene Megameanders

December 30, 2018

Glacial recession during the end of the last Ice Age caused dramatic changes in the climate and river drainages of southeastern North America.  All that melting Canadian ice released moisture into the atmosphere and average annual precipitation in the region tripled to an estimated 47 inches.  But average temperatures were still cooler than they are today and as a result evapotranspiration rates were lower. This increased precipitation and reduced evaporation caused rivers to meander more than they do today.  These supermeanders eroded scars that are still visible in satellite photographs.  Recently, scientists studied 6 paleomeander scars adjacent to the Oconee, Ogeechee, Black, Neuse, Pee Dee, and Congaree Rivers.  These rivers are located in Georgia, North Carolina, and South Carolina.

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Satellite photo of a paleomeander scar located along the Oconee River.  From the below referenced paper.

The scientists found these paleomeanders dated to between ~17,000 years BP-~11,000 years BP.  The scar next to the Oconee River was radio-carbon dated using a 17,000 year old pine log.  The supermeanders cut through the former braided channels that existed during the Last Glacial Maximum when rivers shrank and became clogged with sandbars due to aridity.  Eventually, when present day climatic conditions began to predominate, the supermeanders became cut-off from the main flow of the river.  For awhile they existed as oxbow lakes but then filled with clay and sand.  Scientists estimate the supermeanders were 2-5 times larger than modern meanders and the discharge was up to 4 times larger.  The typical flow was equal to a modern day 5 year flood event.  Scientists aren’t sure of the exact mechanism that caused supermeanders.  It was likely a combination of increased precipitation, low evapotranspiration rates, and seasonal monsoons.  The distance between the frigid air over the Laurentide Ice Sheet and tropical air was much smaller during the Ice Age, and this could have caused an increase in major storm events.

I hypothesize canebrakes and river bottomland forests really expanded during the supermeandering phase.  Canebrakes are a now nearly extinct environment consisting of pure stands of bamboo cane.  Canebrakes formerly occupied hundreds of square miles of river bottomland in the southeast, but European settlers cleared them for agricultural purposes.  They were the most fertile pieces of land in the region.  Canebrakes depend upon a complex regime of flood and fire.  Suppression of either results in the growth of river bottomland forests that shade bamboo out.  During the late Pleistocene canebrakes attracted herds of bison and horses which fed on the nutritious bamboo.  Newly arrived humans facilitated the spread of canebrakes by setting fire to the landscape.  However, canebrakes must have also existed along the braided rivers of the Glacial Maximum, perhaps growing on the sandbars in the middle of partially  dried up rivers. The supermeander oxbow lakes likely hosted the last North American capybaras and giant beavers (Casteroides sp.) before they were hunted into extinction by people.

Reference:

Suther, Bradley; David Leigh, George Brook, and L. Yann

“Megameander Paleochannels of the Southeastern Atlantic Coastal Plain, USA”

Paleogeography, Paleoclimatology, and Paleoecology July 2018

Ice Age Rhythm Shifts

September 10, 2018

For millions of years mild climate allowed soil to build in Canada and the northern regions of Eurasia.  Plants and animals lived and died and their remains turned into thick layers of top soil.  The uplift of the Himalayan Mountains and the Rocky Mountains and the emergence of a land bridge between the Americas changed climate patterns that then became triggered by the Milankovitch Cycles.  (See: https://en.wikipedia.org/wiki/Milankovitch_cycles)  Ice Ages began to occur during the Pliocene over 3 million years ago.  At first Ice Ages lasted for 40,000 years before cycling into interglacial periods.  But about 950,000 years ago Ice Ages began to last for 100,000 years, and they became more severe.  Scientists found evidence suggesting this is when glaciers began to scrape into bedrock instead of the deep soil built up during the Miocene and early Pliocene.  Whereas glaciers slid over soil during earlier Ice Ages, they instead became stuck in bedrock and grew thicker.  Earlier Ice Sheets repeatedly drove into soil and with each Ice Age stripped the soil until 950,000 years ago it finally reached the bedrock.  The increased size of the glaciers caused an increase in the length and severity of Ice Ages.

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Graph showing increased length of Ice Ages.

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Glaciers reached bedrock about 950,000 years ago.  Repeated glacial advances eventually stripped away deep layers of top soil.  Later Ice Ages produced glaciers that got stuck in bedrock and grew thicker.

The evidence for changing Ice Age rhythms comes from deep ocean cores taken from the South Atlantic.  Scientists noticed the sudden influx of isotopes that are more common in the Pacific Ocean in the section of cores dating to 950,000 years ago.  These isotopes of neodymium originate from young volcanic islands located in the Pacific Ocean, and the rock sediment erodes into the ocean and gets carried by currents into the South Atlantic.  Normally, older rocks from coastlines surrounding the North Atlantic Ocean with a different ratio of neodymium isotopes erode and wash into the sea, and they predominate.  But normal ocean circulation shuts down during Ice Ages, and more water from the Pacific Ocean makes its way into the North Atlantic.

Reference:

Vougen, Paul

“Sea Floor Cores Suggest Sticky, Thick Glaciers Caused Mysterious Shift in Ice Age Rhythms”

Science Augusts 22, 2018

 

Does a Clam Know it’s Alive?

August 15, 2018

The late Carl Sagan guessed there might be 1 million civilizations in our galaxy, the Milky Way.  He based this guess on the Drake Equation–a formula that takes the number of stars in the galaxy and multiplies it by fractions of: sun-like stars, sun-like stars with planets, planets in inhabitable zones, planets where life evolved, planets with intelligent beings, and the percentage in the lifetime of a planet with a civilization.  However, the Rare Earth Hypothesis proposed by Peter Ward and Don Lee in 2000 posits microbial life may be widespread in the universe, but complex life must be extremely rare.  Since the Rare Earth Hypothesis was proposed, astronomers have discovered 3600 exoplanets in solar systems outside our own.  The evidence so far indicates the Rare Earth Hypothesis might be the more accurate guess.  Of the 3600 exoplanets discovered just 1 is a rocky earth-like planet that orbits in an inhabitable zone.  It is known as Proxima b. All other planets found in habitable zones are gas giants with no surface, similar to Jupiter and Saturn.  Though Proxima b is located in an habitable zone, it probably does not support life because it is tidally locked, meaning 1 side of the planet always faces its sun.  Half of the planet is too hot, and the other half is too cold.

Complex life evolved on earth thanks to numerous unique characteristics that apparently are extremely rare elsewhere in the galaxy and probably the universe.  Earth is just the right distance from the sun, and the sun is just the right kind of star.  Our sun is bigger than 95% of other stars.  The habitable zones of planets orbiting smaller stars would have to be much closer, but this would make the planets tidally locked like Proxima b or Mercury.  Moreover, most other solar systems are binary.  Solar systems with 2 or more suns force planets to have wild perturbations in their orbits, causing a great frequency of cosmic impacts that extinguish complex life.  Earth is the only known planet with abundant tectonic activity which helps control CO2 buildup.  Without tectonic activity CO2 concentrations in the atmosphere amplify heat and scorch complex life into extinction.  Venus is an example of this kind of uninhabitable world.  And earth is lucky to have a large moon that stabilizes earth’s tilt.  The earth’s tilt varies between 23.5-25 degrees, but planets without a large moon may vary in their tilt by up to 90 degrees.  The resulting climate instability would cause the complete extinction of complex life.

Microbial life first evolved on earth about 4 billion years ago, but complex plants and animals don’t appear in the fossil record until about 700 million years ago–a colossal gap in time.  Most earth-like planets in the universe probably resemble the early earth of 2.5 billion years ago.  The earth of that time was mostly ocean with a few volcanic islands.  The ocean was brown from cosmic-impacted debris, and the sky was red in an atmosphere of little free oxygen.  Eventually, plate tectonics formed continents, and shallow water environments supported greater populations of photo-synthesizing bacteria that produced enough oxygen to support complex life.

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Illustration of early earth’s atmosphere.  Land was restricted to a few volcanic islands and the sky was red in an atmosphere with little free oxygen.

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Early microbial life on earth resembled these primitive thermophilic Archaea.  They can survive in temperatures exceeding the boiling point.  This suggests microbial life may be widespread in the galaxy, though complex life is much more rare.  It took over 3 billion years for microbial life to evolve into complex life on earth.

Though complex life must be rare, there are between 1-2 billion galaxies in the universe, each with up to 1 billion stars that in turn have close to 10 planets in their systems.  The universe is so vast complex life likely evolved elsewhere besides earth.  But why?

I think the universe would not exist without complex life aware of its existence.  Suppose complex life never evolved anywhere.  Sure, there could be billions of galaxies, but if there was nothing aware of all that matter, it might as well not exist.  No sentient being would know it was there, so it would not be there.  This is why I think the universe produces worlds where complex life evolved.  It is an attempt by the universe to exist.  It becomes self aware through the minds of many individual sentient beings.  This complex life can’t be just a tree or a clam or a thermophilic micro-organism.  I doubt those living things are aware of their own existence let alone the existence of the universe.  Dogs and cats are aware of their existence, but I doubt they contemplate the existence of the universe.  Give them a smelly piece of meat and a caress and that’s as far as their in depth thought of the universe goes.  I believe the universe strives to produce life that recognizes it exists.  Otherwise, it will cease to exist or it may as well not exist because no sentient being would know of its existence.  Without complex life equivalent or above the intelligence of humans, the universe would have no knowledge of its existence, so it would not exist.

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I doubt a clam knows it is alive.  I believe the universe depends on life more complex than this for its existence.  The existence of complex life and the universe is an interdependent relationship.

Reference:

Ward, Peter; and Donald Brownlee

Rare Earth: Why Complex Life is Uncommon in the Universe

Copernicus 2000

 

Surprise: Increased Hurricane Activity During the Younger Dryas

November 28, 2017

 

The vast ice sheet that covered Canada during the last Ice Age began to melt rapidly about 15,000 years ago, creating enormous glacial lakes. The largest glacial lake, known as Lake Aggasiz, was bigger than all of the present day Great Lakes combined.  The ice dam impounding this incredible volume of water collapsed 12,900 years ago, and a massive flood of cold freshwater, icebergs, and debris gushed into the North Atlantic via the St. Lawrence River.  This event caused a sudden drop in global temperatures and a reversal back to Ice Age conditions at northern latitudes because the influx of cold fresh water shut down ocean currents that brought tropically-heated salt water north.  The cold climate phase lasted for about 1500 years, and climate scientists refer to it as the Younger Dryas.

The colder ocean of the Younger Dryas should have spawned fewer hurricanes than the warmer oceans of today.  Hurricanes are a product of energy released from warm ocean water.  However, scientists discovered evidence hurricane activity increased off the coast of Florida during the Younger Dryas.  They discovered deposits of turbidite near the Dry Tortugas Islands, dating to the Younger Dryas.  Turbidite is sediment and rock resulting from underwater perturbations.  Earthquakes can cause turbidite formation, but this region is not prone to seismic activity.  Instead, hurricanes produced underwater currents that formed turbidite here.

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Map of the Dry Tortugas–site of the study referenced in this blog entry.

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Image showing how turbidite deposits are formed.

Scientists aren’t sure why hurricane activity increased during the Younger Dryas at this locality.  Some of their climate models suggest the oceans were much colder to the north and west of the Florida coast but only slightly colder than present day ocean temperatures off the modern Florida coast.  Perhaps the tropically-heated water that pooled near the equator spawned hurricanes that reached the Florida and south Atlantic coasts.

Increased hurricane activity contributed to the expansion of longleaf pine savannahs.  The wind felled forests, and the accompanying lightning-sparked fires maintained longleaf pine savannah ecosystems while repressing closed canopy hardwood forests.  Pleistocene megafauna became extinct during the Younger Dryas, even though longleaf pine savannahs are ideal habitat for grazers such as mammoths, bison, horses, giant tortoises, and many other species.

Reference:

Toomey, M. ; et. al.

“Increased Hurricane Frequency Near Florida during Younger Dryas Atlantic Meridional Overturning Circulation Slow Down”

Geology 45 October 2017

 

 

 

 

Sand Dunes Rolling Across the South

May 25, 2017

Ice Age environmental conditions influenced the present day landscapes of many geographical localities, including the Carolina Sandhills.  A recent study determined Ice Age winds shaped the topography of this region.  The sand originated from loose sediment and eroded sandstone within a Cretaceous-age formation located near the surface.  Arid climatic conditions caused by glacial expansion exposed part of this formation.  Frequent droughts reduced vegetative cover, so there were bare patches of soil without tree and grass roots holding the sand in place.  I think overgrazing by megafauna during droughts played a role in denuding the landscape as well.  Cold winds blew the exposed sand into massive eolian dunes that rolled across the land.

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The Sand Hill Region is encircled in red on this map.  At least parts of it originated during Ice Ages when cold winds blew exposed sand across the landscape here.

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Vegetation stabilizes sand dunes in the region today.  Local sand dunes have been inactive for at least 6,000 years.  They were most active during the coldest driest phases of Ice Ages.

The authors of the below referenced study took core samples of sand hill sediment in Chesterfield County, South Carolina.  They found an unconsolidated layer of sand measuring from ~1 foot to about 30 feet deep.  Optically stimulated luminescence dates (See: http://www.usu.edu/geo/luminlab/whatis.html ) suggest dunes were active from 75,000 years BP-37,000 years BP when glaciers were expanding and from 28,000 years BP-18,000 years BP during the Last Glacial Maximum and again from 12,000 years BP-6,000 years BP.  The beginning of the final period of dune activity corresponds with the Younger Dryas cold reversal when average global temperatures suddenly plummeted following a warm climate cycle.  Scientists found no evidence of dune activity between 37,000 years BP-28,000 years BP and 18,000 years BP-12,000 years BP.  These dates correspond with warmer wetter interstadials when plant growth stabilized sand sheets and dunes, holding them in place.  There has been no dune activity in the Carolina Sandhills for at least 6,000 years because higher precipitation levels foster thicker vegetative growth.

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The Great Kobuk sand dune in Alaska.  During the Ice Age landscapes in the sand hill region may have resembled this, though short leaf pines, grass, and scrub oak as well as spruce were the characteristic vegetation between the dunes instead of just spruce.

Sand dunes probably advanced the most on cold windy Ice Age nights.  Experiments show air temperature is a factor in sand particle transport.  Decreasing temperatures increase air density and lower water vapor thus reducing drag on the sand particles.  Larger particles can get picked up and transported by wind more easily when temperatures drop.  The region may have experienced brutally low temperatures compared to present day averages.

Sand dune origin in the Carolina Sandhill region differed a little from sand dune formation in Georgia.  The source of sand in the Carolina Sandhills is a geological formation near the surface, but many dunes in Georgia originated from dry river beds where sand was exposed because water tables dropped.  (See: https://markgelbart.wordpress.com/2012/04/09/the-ohoopee-sand-dunes/ ).

Pollen evidence indicates the dominant flora growing between the sand dunes during the Ice Age consisted of pine, spruce, scrub oak, grass, and asters (sunflowers, daisies, etc.).  It was probably an open woodland type of environment, though scrub oaks may have formed denser thickets.  I believe shortleaf pine (Pinus echinata) and possibly Virginia pine (P. virginiana) were the dominant species of pine here then.  It was too cold and windy for longleaf pine (P. palustris), commonly found here today.  I’m no longer convinced jack pine (P. banksiana) occurred this far south.  Some pollen studies list jack pine as a species present in this region during the Ice Age.  However:

1)The present day range of jack pine is too far away from the Carolina Sandhills. It seems unlikely its range would have retracted so drastically without leaving a relic population anywhere in the south.

2)  There are no definitive macrofossils of jack pine in the south.

3) Evidence jack pine was present in the south is based on identification of pine pollen, but 1 researcher makes the compelling case that jack pine pollen is indistinguishable from shortleaf pine pollen.  (See: https://www.osti.gov/scitech/biblio/564104 ).  Jack pine pollen is distinguished from other species of pine pollen based on the size of its grains but they overlap in size with shorleaf pine pollen grains.  Because shortleaf pine occurs in the region today, it seems more likely pollen evidence represents this species, not jack pine.

The species of spruce tree present in the Carolina Sandhills during Ice Ages was probably the extinct Critchfield’s spruce.  Macrofossils of this species have been found associated with temperate species of hardwoods.  The average annual temperatures of the Carolina Sandhills during Ice Ages was probably similar to present day southern Ohio or Kentucky, not like southern Canada as some researchers estimate based on their mistaken assumptions of tree species composition.  The Carolina Sandhills are located in what was a sharp transition zone of climate during the Ice Age.  A thermal refuge existed to the southeast where warm waters off the Atlantic coast pooled because thermohaline circulation (the tropically heated water that presently flows off the coast of New England) shut down.  But temperatures sharply dropped to the north and west of this thermal refuge, not unlike conditions experienced by mountain climbers rapidly ascending a mountain.

The Carolina Sandhills likely supported significant populations of megafauna, despite the vast expanses of bare sand.  Open grassy land fed mammoths, caribou, horses, bison, llamas, and Harlan’s ground sloth.  Scrub oak thickets attracted herds of flat-headed peccaries.  Giant lions and dire wolves roamed the interdunes, seeking out megaherbivores.

Reference:

Swezey, Christopher; et. al.

“The Carolina Sandhills: Quaternary Eolian Sand Sheets and Dunes along the Updip Margin of the Atlantic Coastal Plain Province, Southeastern United States”

Quaternary Research 86 (2016)

The Most Cataclysmic Ice Age Floods

February 11, 2017

Climate patterns were different during Ice Ages.  The Rocky Mountain region of North America is mostly arid today, but more precipitation and lower rates of evapotranspiration led to the formation of vast lakes during cooler climate phases.  Most of these lakes gradually disappeared in non-dramatic fashion after the climate became warmer and drier.  Evaporation changed the former sites of these freshwater lakes into empty basins, salt plains, and much smaller salt lakes.  But the demise of Glacial Lake Missoula caused a spectacular flood, perhaps the largest deluge in earth’s history.

A southern lobe of the Cordilleran Ice Sheet blocked the flow of the Clark Fork River near the border of present day Idaho and Montana, creating a glacial lake as big as Lake Erie and Lake Ontario combined.  At times it was almost 2000 feet deep, though it periodically lowered and partially drained.  The ice dam itself was an astonishing 2000 feet high.  The warm climate phase that marked the end of the Ice Age beginning about 15,000 years ago melted the ice dam, and the tremendous volume of water in Lake Missoula burst across Idaho and eastern and central Washington, finally emptying through the Columbia River valley into the Pacific Ocean near the present day town of Astoria, Oregon.  This massive flood created a landscape known as the “channeled scablands.”  The geological formations that serve as evidence of this cataclysm are impressive and picturesque.

Areal Scenario Map of the Ice Age Floods - Click to View Larger Image

The largest floods in the history of North America occurred in the Pacific northwest following the end of Ice Ages.

Image result for Channeled scabland

These geological landforms were caused by post Ice Age floods.

Below is a link to many more photos of these formations.

http://hugefloods.com/Scablands.html

The flood carried large boulders encased in icebergs.  These “erratics” can be found throughout the channeled scablands.  There are dry falls–350 foot tall hills under where 300 feet of Lake Missoula water formerly flowed in what were temporary waterfalls.  Huge ripple marks can be seen on Camas Prairie.  Other amazing formations are the kolk potholes where swirling eddies gouged out deep troughs.  Strandlines and lake deposits visible on the sides of mountains are evidence the dissolution of glacial lakes occurred repeatedly in this region–perhaps more than 34 times during the Pleistocene.

The scouring of these intermittent Ice Age floods eroded most of the topsoil in this region and much of the scabland is unsuitable for crops.  But there are some exceptions.  The tops of some hills were above the flood and still have enough soil for growing crops, and some soil eroded from mountains into some valleys where crops can also be grown.  But for the most part agricultural activity here is limited to livestock grazing.

Humans began colonizing North America about the same time this cataclysmic flood occurred. Any people in the path of the deluge perished.  Members of the sparse population living on the edge of the flood witnessed an unusual, awe-inspiring event, a story they likely told their children and grandchildren.  It may be the origin of ancient flood myths found in Native American lore.  Flood myths are known in cultures worldwide and probably are based on inherited memories of local floods that occurred at the end of the Ice Age when glaciers melted and sea level rose rapidly.

Reference:

Smith, Larry

“Repeated Sedimentation and Expanse of Glacial Lake Missoula Sediments: A Lake Level History of Garden Gulch, Mountain, USA”

Quaternary Science Review January 2017