Advancing and retreating glaciers during Ice Ages crushed rock into dust. Meltwater pulses that occurred when climate cycles shifted to warm stages washed this dust into rivers. Then, when climate cycles shifted to arid stages and rivers shrank in size, exposing the sediment, wind blew this dust into huge hills alongside the rivers. This wind-blown dust is known as loess. Hills made from loess are located up and down the Mississippi River Valley, but today they are covered by vegetation that originally took root when climate became more moist and warmer. Land snail shells are often found in the loess. Scientists can use the snail species composition to estimate past average summer temperatures. (Land snails are mostly active during the warmer months.) Every species of snail occurs in ranges within certain temperature parameters. Scientists can also radio-carbon date snail shells. By dating the subfossil snail shells and identifying the species present, scientists can estimate past average summer temperatures.
Map showing where hills made of Ice Age loess sediment are found.
Road cuts reveal loess sediment.
This species of land snail requires warm summers and is evidence of warmer climates.
This is another species of land snail that indicates warmer summers.
The presence of this species indicates cooler summers, like those that occurred during Ice Ages. They still occur in Canada.
Another species of snail that requires cooler summers.
Scientists determined average annual summer temperatures in the upper Midwest near the glacier edge fell drastically about 27,000 years ago–the beginning of the Last Glacial Maximum. Before summer temperatures fell, species of snails favoring warm climate including Anguispira kochi, Hawaii minisculs, and Vallonia perspectiva are found in sediment dating between 30,000 years BP-27,000 years BP. After this for the next 12,000 years snail species that require cool summers are found in the sediment. These species include Columella alticola, Vertigo modesta, and Vallonia gracilicosta. In all scientists found 68 species of terrestrial snails from 4 genera at the study sites. The sites were from 14 midwestern states. Each site had from 5-30 species.
During the Last Glacial Maximum summer temperatures near the glacier margin averaged 6-18 degrees F cooler than those of today. Summer averages were 59-61 degrees F. Near the Gulf Coast summer average temperatures were 77 degrees F compared to 92 degrees F today. The results of this study are consistent with climate data from ice cores, ocean sediment, and pollen composition.
References:
Grimley, D.; and J. Conroy
“Last Glacial Maximum Summer Temperature Gradient from Terrestrial Gastropods in Peoria Silt (loess), Midwestern USA”
Quaternary Science Reviews June 2026
Grimley, D.; et al
“Last Glacial Maximum Ecology and Climate from Terrestrial Gastropod Assemblages in Peoria Loess, Western Kentucky”
I’ve always been fascinated with the Sangamonian Interglacial, known as the Eemian Interglacial in Europe. It’s the most recent climate phase when average annual global temperatures were the same or even higher than those of today. No major extinction of megafauna occurred during this phase–the best evidence against climate models of Pleistocene megafauna extinction. The Sangamonian Interglacial lasted from 132,000 years BP-118,000 years BP, although the below referenced study frames it between 128,000 years BP-117,000 years BP. Climate was likely not noticeably different during the discrepancy between these 2 parameters. The north polar ice cap completely melted during the Sangamonian Interglacial, resulting in higher sea levels than today. The north polar ice cap also completely melted during the early Holocene about 10,000 years ago. (Note: and polar bears did not become extinct as alarmists claim will happen.) Scientists are also interested in the Sangamonian because it provides an analogue for today’s climate but without the influence of manmade greenhouse gases. Recently, scientists studied ancient shorelines that existed during the Sangamonian Interglacial at Myrtle Beach, South Carolina. They appear today as ridges or terraces, referred to as outcrops as well, and they consist of crushed consolidated seashells including coral, clams, and oysters. 1 of these outcrops has a layer of peat inside the shelly sediment, suggesting the existence of a marsh, and another 1 has an eolian or windswept sand dune embedded in the layer from dunes that formed during an arid climate cycle.
Location of the area studied in the below referenced paper. Yellow lines represent high stands. Peninsular Florida was mostly submerged with the exception of a few islands. During the Pliocene shoreline was even higher and extended into the middle of South Carolina where the shoreline consisted of sea cliffs. Today, it is the eroded Orangeburg Escarpment.
Another map from the below referenced study showing terraces from former shorelines when sea level was higher than today.
Cold water coral (Desmophyllum pertusum) occurs on the Blake Plateau off the coast of South Carolina. It forms an important ecosystem. Scientists date ancient shorelines using radiometric dating, specifically Uranium series dating of coral found in the terraces.
Ribbon corals, also known as sea whips occur in shallow water off the coast of South Carolina. They are not a true coral.
The scientists dated these old shoreline ridges using uranium series dating from coral fossils and by using optically stimulated luminescence. (See: https://en.wikipedia.org/wiki/Optically_stimulated_luminescence ) They determined sea level rose no more than 15 feet during the early Sangamonian. Throughout the Sangamonian sea level fluctuated between 9-21 feet higher than that of today. Sea level rose rapidly during the early Sangamonian, stabilized, then rose again. Fluctuations were rapid and corresponded with unstable ice sheets. This new study agrees with earlier studies of these marine high stand terraces at other locations. During Ice Ages sea levels retreated as more of earth’s moisture became locked in glaciers, and dry land habitat occurred as much as 50 miles off the modern-day coast.
Reference:
Dean, S.; et al
“Last Interglacial Relative Sea Level Changes at Myrtle Beach, S.C.”
Google searching for answers and research is much easier now. Google AI answers the questions, and there is no need to scroll through pages of websites to find a satisfactory answer. I suspect Google AI is responsible for reducing the average daily views to my site by 50% over the past 6 months, but it doesn’t matter because I don’t make any money doing this. It’s just a hobby for me, and I don’t feel bad for the owners of WordPress.
I’ve always been fascinated with adobe houses. They are built using primitive technology yet are comfortable and especially able to keep indoors cool in the American Southwest where they are most prevalent. American Indians built adobe houses, and some were built embedded on mountainsides where they were accessible by ladders which could be withdrawn, keeping the people in them safe from other hostile tribes. My fascination led me to read Woody Guthrie’s only published novel House of the Earth. Guthrie wrote “This Land is Your Land” and was a great folk song writer, though he was a stupid communist. His novel, written in 1947 but not published until recently, is a good example of really bad writing. The corny dialogue is tedious and pointless, and Guthrie sometimes uses a dozen similes to describe 1 thing, a style of gross overwriting that I found hard to endure. Moreover, in the novel, the characters never get to building their adobe dream house–the part I was most looking forward to reading. How unfulfilling.
I asked Google AI whether an adobe house could withstand a F5 tornado. Tornadoes are rated according to the Fujita Scale, and an F5 is the most devastating with winds that exceed 200 mph. Google AI emphatically said no. I then asked Google AI for an example of an adobe home destroyed by any scale of tornado, and it was unable to give any, though it still insisted a tornado would destroy an adobe home.
An F5 tornado will obliterate almost anything in its path.
Map showing area where adobe homes are common in the U.S. The eroded sedimentary rock found in this region is good for making adobe brick.
Many tribes of Southwestern Indians used adobe brick.
This is a really attractive adobe home.
Another nice adobe home. Authentic adobe homes usually have flat roofs, but this one has a modern roof.
Reinforced concrete with embedded steel can survive a direct hit from a tornado.
Dome-shaped homes can also survive tornados because of aerodynamics. The shape deflects high winds and distributes pressure evenly, and there is no weak point that attaches the roof to the walls. An adobe home shaped like a dome could also survive a tornado, so I propose Google AI is wrong about this.
Adobe homes are made from sun dried bricks as opposed to regular bricks which are dried using heat. Straw is mixed with the local soil and dried in piles. The walls of an adobe home can be made several feet thick and can keep inside temperatures constant, like a cave. The roofs are made with poles, lattices, and branches held together with adobe. The roofs are often flat. Adobe houses can be built in Georgia, where I live, but they need large overhangs to prevent precipitation from eroding the walls. Usually, an extra coat of cement plaster or stucco attached to iron mesh is used to give the adobe home a better look.
Tornadoes destroy homes by causing internal pressure on the home that makes it implode. The wind tears the roof off, and windblown debris also can cause severe damage to homes not directly in its path. Tornado proof safe rooms can be built using concrete reinforced with embedded steel. There is more than 1 case of a dome-shaped structure withstanding tornadoes due to the aerodynamic nature. The shape deflects the wind and distributes the internal pressure evenly. Google AI might be wrong. An adobe house built in a dome shape could possibly still stand after a hit from an F5 tornado.
Dry climates prevailed worldwide during Ice Ages because so much of earth’s atmospheric moisture was locked into massive Ice Sheets. Less precipitation meant less vegetative cover, and with fewer plant roots holding soil into place, the strong winds, also caused by Ice Sheet expansion, blew dirt and sand great distances. Some settled into huge sand dunes; other particles were blown all over the planet into the oceans and as far north as Greenland. Scientists take ice cores from the 125,000-year-old glacier in Greenland, and they have a year-by-year diary of past climatic conditions. Rings from summer melting mark the years exactly. Oxygen isotope ratios from air bubbles trapped inside the annual rings help scientists determine past average annual temperatures, but they also can determine how dry the climate was based on the quantity of dust and sand from inside each annual ring. The quantity of dust particles deposited was highest during the dryest years of the Ice Age.
Pleistocene sandstorms were fatal to the animals and plants buried under the dust. Animals that escaped these massive storms still suffered, perhaps fatally from getting the dust in their lungs. These sandstorms benefitted Pacific Ocean ecosystems because iron from sediment blown into the ocean fed phytoplankton, the base of the food chain. Scientists think most of the minerals came from the Gobi Desert which expanded during Ice Ages. Some recent studies suggest dust storms in Europe were even larger when they occurred during late winter and early spring. In North America, especially along the Mississippi River, waterways shrank, and exposed riverine sands blew into large dunes, still visible today.
Sand blown from the Gobi Desert during Ice Ages fertilized the Pacific Ocean.
Windblown sediment from the edge of Ice Age glaciers and exposed riverine sand blew into huge dunes still visible today.
Map showing where windblown sediment deposited from melting glaciers settled. This sediment is known as loess.
This diagram shows how dust particles were deposited into the Greenland Ice Sheet. The ice core rings are an annual diary of climate going back 125,000 years.
These are the types of minerals found in ice cores. Iron-rich minerals fertilized oceans.
The best facsimile of these ancient dust storms from the historical record occurred during the Dust Bowl era of the 1930’s. The ravages of World War I reduced Russian and European production of wheat. American farmers took advantage of the high wheat prices and ploughed over all the prairie grasses in order to plant as much wheat as possible, and at first they thrived because they planted during an unusually wet weather cycle. Starting in 1930 several years of severe drought shriveled all the plants, leaving thousands of square miles bare of any vegetation. High winds blew this dried out soil as far east as the Atlantic Coast. In the dust bowl area including Oklahoma, Texas, New Mexico, Kansas, Nebraska, and Colorado; the dust was so thick it covered houses, cars, and livestock. Many of the farmers left, leading to the famous Okie migration to California. In response to this disaster the government used the Civilian Conservation Corps to plant 200 million trees and created the Great Plains Shelter Belt. The government also advised famers to use better farming techniques such as contour ploughing (perpendicular to hills) and crop rotation to reduce soil erosion. Some programs even pay farmers not to plant–a socialist policy modern conservative farmers still use, demonstrating their political hypocrisy.
Main area of the 1930’s dust bowl disaster.
Poor farming practices led to this scary disaster.
The dust covered everything and caused health problems. The dried-out soil carried diseases and pesticides that made people suffer from long term health problems.
The extinction of all dinosaurs (except birds) at the end of the Cretaceous Age was made famous 45 years ago when a crater was found in the Gulf of Mexico–confirming a comet impact as the cause of the extinctions 66 million years ago. A lesser-known local extinction of dinosaurs occurred 145 million years ago at the end of the Jurassic Age. From geological and paleontological evidence scientists determined dinosaurs were diverse and abundant in western North America from 152 million years ago to 145 million years BP, but these species became extinct after a sudden cataclysmic event. Scientists suspect a mega volcano eruption rubbed out all the dinosaurs in this region then. During the late Jurassic sauropods such as diplodocus (the largest known land animal in earth’s history), allosaurs, stegosaurs, and small ornithomimids (bird-like dinosaurs but not ancestral to birds) dominated the faunal composition. After the extinctions Cretaceous Age species gradually colonized the region and ecologically replaced the Jurassic Age species, although sauropods continued to live in other regions of the earth. Iguanodons, ankylosaurs, and smaller species of ornithomimids were the new inhabitants of the region. The early Cretaceous dinosaur composition was less diverse in this region than the late Jurassic.
The Morrison formation consists of sedimentary rocks that have the best evidence of Jurassic Age dinosaurs in North America.
Scientists found an interesting faunal turnover between the late Jurassic and the early Cretaceous in the Morrison Formation located mostly in Utah. Poster from James Kirk’s twitter feed.
Plant fossils from the Morris Formation include conifers, cycads, and ancestors of ginko.
The northern part of the Morris Formation yielded fossil remains of a different species of allosaur than the southern part. Scientists don’t know why 2 different species evolved. They don’t know of any physical barrier between the 2 areas.
Sauropods like this diplodocus and stegosaurs were the main species of large plant-eaters in western North America before the Jurassic Morrison extinctions.
Stegosaurs didn’t make it to the Cretaceous.
Evidence of this faunal turnover comes from the Morrison Formation–mountains of sedimentary rock found in western North America, mostly Utah. During the late Jurassic this area was a floodplain bordered by a newly forming mountain range. Cycads and conifers grew on the plain, and rivers flowed from the mountains into a vast marshy lake. Some of these trees have been preserved in petrified forests located in Dinosaur National Monument. The northern and southern part of this region hosted 2 different species allosaurs and 2 different species of carnosaurs. Scientists haven’t figured out why the northern and southern parts of this region had different species of carnivorous dinosaurs. They know of no physical barrier that would have contributed to this speciation. The region shifted frequently between wet and dry climate cycles, but scientists don’t think this was a factor in the sudden extinctions of Jurassic Age dinosaurs here. Dinosaurs were thriving and diverse up until their sudden end here.
Reference:
Kirkland, J.; E. Sampson, M. Wizecurch, and D. Deblieux
“Paleosols in the Lower Yellow Cat Member of the Cedar Mountain Formation in Eastern Utah Indicate the Earliest Cretaceous (Borrasian) in the Colorado Plateau was Exceptionally Wet”
75th Annual Meeting of the Rocky Mountain Geological Survey 2025
Maidmont, S.
“Diversity Through Time and Space in the Upper Jurassic Morrison Formation, western USA”
Whenever I’ve discussed anthropogenic global warming on this blog, I’ve often written climate models were wild guessing. I’ve come across a study that suggests I was wrong. The study looked at 11 scientific papers with 14 projection models that estimated changes in average global temperatures over time. The papers were published between 1970-1993. The authors of this study then compared those projections from the models to average temperatures as of 2017. Though some models slightly overestimated temperatures and others slightly underestimated temperatures, most were remarkably consistent. The models were based on estimates calculating natural climate change plus manmade emissions of CO2 influence.
Climate models were remarkably consistent with real observations. Chart from the below study.
Energy use is projected to increase exponentially in the future, and this means an increase in burning fossil fuel and even greater CO2 emissions. The creation of bitcoins alone equals the energy use of New York state or the country of Poland. I don’t understand how cryptocurrency is even legal. Bitcoin creators are wasting earth’s resources creating artificial wealth out of nothing. Data centers that support internet infrastructure already use almost 5% of the power generated in the world. This computational infrastructure is going to increase as humans rely more and more on robots.
Bitcoin mining uses an enormous amount of energy, creating nothing that is useful for society. A few people will get rich at the expense of a lot of chumps.
Data centers will expand, as humans rely more and more on robots, hence increasing energy use even more.
As more fossil fuel is used, earth’s climate is headed for an uncomfortable atmosphere that resembles what it must have been like for dinosaurs during the Cretaceous Age. There is no reversing this nightmare scenario. People aren’t going to give up driving cars and central heating and air conditioning. (Especially air conditioning, since the world is going to become so much warmer.) Selfish totalitarian rulers don’t care about the environment. Wind and solar won’t be able to provide enough power for the world to end use of fossil fuels. We are doomed to live in a world of misery caused by climate change.
Robots will contribute to an apocalyptic future, but probably not in the way depicted in the Terminator movies. Instead, the energy demand to drive robots will cause global warming that will devastate the atmosphere.
Reference:
Hausfather, Z.; H. Drake, T. Abbott, G. Shmidt
“Evaluating the Performance of Past Climate Model Projections”
I get so annoyed at news reporters and political pundits when they talk about climate change because they invariably get climate confused with weather. All summer long, reporters were warning about how awful the upcoming hurricane season was going to be, and they always blamed anthropogenic-influenced climate change. Then, hurricane activity this year was below average (so far). Few of these same reporters mention this. A hurricane season is weather, not climate. The definition of climate is the long-term weather pattern of a region based on at least 30 years of data. Another ignorant statement made by reporters and pundits is how the recent increase in average annual temperatures is unprecedented. This misinformation is easily demonstrated as false. Average annual temperatures over the past 150 years have increased by less than 2 degrees F. This isn’t even close to being unprecedented. 14,700 years ago, average annual temperatures increased by 18 degrees F in a period of 10-20 years. This warming event began the Boling-Allerod Insterstadial which lasted until 12,900 years ago when average annual temperatures plummeted to full Ice Age conditions, also in less than 2 decades. Then, again 11,000 years ago average annual temperatures abruptly increased by 18 degrees F in a few decades, beginning the Interglacial conditions we currently enjoy. Contrary to alarmist news reporters and pundits, earth is experiencing a period of relative climatic stability.
Average annual temperatures over the past 100,000 years.Note how stable temperatures have been for the past 10,000 years. Note also how many abrupt warm changes have occurred. The increase in average annual temperatures over the past 150 years doesn’t even show up on this graph compared to past changes.
Data from Greenland and Antarctic Ice Cores. Average annual temperatures are calculated from oxygen isotope ratios found in ice core layers. Note the spike in temperatures about 14,700 years ago.The change was less pronounced in Antarctica.
Sea surface temperatures calculated from data extracted from deep sea sediment cores correlatewell with data from Greenland ice cores. From 60,000 years BP-30,000 years BP there were frequent abrupt warming events that far surpassed the average annual temperature increase from the past 150 years.
Scientists have interesting ways of determining past climate. They take cores of ice in Greenland from a glacier that has existed for over 100,000 years. The cores can be easily dated because they have annual rings that form every summer when the glacier partially melts. The scientists examine the oxygen isotope ratios from air bubbles within each annual layer, and they can calculate the average annual temperature from that year. Oxygen isotope ratios vary depending upon whether the ice is melting (summer) or accumulating (winter). They also look at dust concentration. High levels of dust suggest cold arid climates with less vegetative cover; low levels of dust indicate warm humid climate. Another method of determining past climate is to examine deep sea sediment cores. The layers are carbon dated, and scientists look at the chemical isotope ratios and species composition of foraminifera present in each layer. Foraminifera are tiny organisms with shells that can be chemically analyzed, and species vary depending upon temperatures. Some of the more utilized cores come off the coasts of Bermuda and Venezuela. This gives us an excellent record of past climates. The data from Greenland ice cores, tropical deep sea sediment cores, and ice cores from Andes Mountain glaciers is remarkably correlated, showing abrupt warming events occurred from Greenland to well into the tropics. However, ice core data from Antartica suggest these abrupt warming events were less pronounced in the Southern Hemisphere.
The occurrence of an abrupt warm shift of climate 14,700 years ago baffles scientists. It’s a confounding mystery. These events don’t fit any of the statistical models used by climate scientists to estimate future climate scenarios that figure in anthropogenic factors. Scientists can’t understand how earth’s average annual temperatures reached modern day parameters when ice sheets still covered most of Canada and northern Europe. From ~29,000 years ago to 14,700 years ago earth was locked in a stable Ice Age, then for no apparent reason temperatures rose dramatically. Scientists believe the difference in average annual temperatures were entirely due to changes in winter temperatures. A study of fossil beetle species composition in Great Britain determined winter temperatures during the Ice Age were similar to modern day temperatures found in Siberia. Summertime temperatures were about the same as today. The abrupt shift to average annual temperatures was the result of much milder winters, such as occur in Great Britain today. 12,900 years ago, winter temperatures plummeted back to Ice Age levels, but scientists understand why this happened.
Scientists know how thermohaline cycles influence climate. Today, the Gulf Stream carries warm currents from the tropics north and this keeps northern Europe and New England relatively mild during winter compared to the Ice Age condition of brutal winters. Thermohaline circulation was weak during most of the Ice Age and shut down completely during the Younger Dryas cold stage that began 12,900 years ago. Thermohaline circulation is active during warm phases of climate. Following abrupt warm shifts during the Ice Age, ice dams that created huge glacial lakes melted, and the flood of fresh cold water into the North Atlantic shut down the Gulf Stream. Changes in thermohaline circulation explain sudden shifts to cold climate phases, but they do not explain what causes sudden warm shifts.
Possible explanations for these abrupt warm shifts in climate include glaciers reflecting sunlight into the atmosphere causing earth’s atmosphere to warm, changes in zonal winds that bring warm tropical air into higher latitudes, and the Gulf Stream shifting east. None of these explanations fits any model, nor are they satisfactory. Scientists are awaiting a breakthrough theory to solve the mystery of abrupt warming events.
Reference:
Schneider, T.; and A. Sobel
The Global Circulation of the Atmosphere
Seager, R. and D. Battisti
Chapter 12: “Challenges to our Understanding of the General Circulation: Abrupt Climate Change”
My family moved from Ohio to Georgia during 1976 when I was 13 years old. I occasionally wonder how my life would have been different if we never would have moved. Would I have a blog entitled Ohio Before People instead of Georgia Before People? My interest in Pleistocene mammals began before we moved when I read a Time Magazine article about saber-toothed cat bones found at the First National Bank Site in Nashville, Tennessee. Maybe I would’ve had a natural history blog focusing on Ohio instead of Georgia.
Evidence of Pleistocene Ice Ages is abundant in Ohio because glaciers repeatedly advanced and receded over the state. Scientists believe there were 17 major glacial advances in Ohio over the past 3 million years, but geological evidence exists for just the last 2–The Illinoian (230,000 years BP-132,000 years BP) and The Wisconsinian (118,000 years BP-11,000 years BP). These last 2 glacial advances scoured away geological evidence of the previous 15, and the only geological evidence of the Illinoian glacial advance is south of where the glacier advanced during the Wisconsinian Ice Age. During the Illinoian Ice Age the glacier advanced all the way into northern Kentucky.
The following is the geological evidence of Ice Ages in Ohio.
Map showing the maximum extent of the most recent glacial advance during the Wisconsinian Ice Age. During the previous Ice Age, The Illinoian, the glacier advanced even further into northern Kentucky.
Lake Erie
All the Great Lakes were formed from melted Ice Sheet. Before Ice Ages began, the now extinct Erigan River System flowed through where the Great Lakes exist today. The advancing glacier took the route of least resistance and scoured out lake basins in this former river valley. There is no evidence of Great Lakes following previous Ice Ages, but it is likely there were previous incarnations of the Great Lakes. Present day Lake Erie is only 5000 years old, and it evolved from previous post-glacial lakes.
Kettle Lakes
Punderson Lake, a kettle lake in Ohio. Our family went for a picnic here in 1967 when I was 5 years old. A kettle lake is a melted chunk of glacier left behind when the glacier retreated.
Ohio is dotted with kettle lakes. They were formed when the glacier retreated but left big blocks of ice behind in low lying areas. Sometimes these blocks of ice became buried in sediment. Eventually, this melted ice became a small lake.
Kames
A kame in Scotland. (I couldn’t find a good photo of 1 in Ohio). Kames are sandy knobs that were outwash of sediment carried by meltwater streams on top of the glacier. When the glacier underneath melted, they slumped, but many are still higher than the surrounding terrain.
When the glacier was in the process of retreating, meltwater floods and wind often carried sediment on top of the ice sheet. This sediment piled up into hills. Eventually, the ice underneath melted, and the sediment slumped but was still higher than the surrounding terrain.
Moraines
Diagram showing sediment pushed forward by a glacier and left behind after it recedes.
Moraines are sediment pushed in front of glaciers. They appear as hills and show how far the glacier advanced. Glaciers alternately advanced and retreated. The most southerly moraines in Ohio show the farthest extent of glacier advance during the Last Glacial Maximum. Recessional moraines show where glaciers re-advanced during cold climate fluctuations after the Last Glacial Maximum. Spruce tree logs are commonly found buried in the moraines, showing where glaciers rapidly advanced through forests.
Outwash
The glaciers often melted rapidly, and the meltwater flooded down stream and river valleys carrying loads of sediment including gravel and sand. This sediment can be found in stream-like patterns throughout the state, though they are covered with vegetation. There are also lake sediments where the glacier blocked streams and rivers, forming temporary glacial lakes that eventually drained.
Erratics
Erratics are large bouldersleft behind by retreating glaciers. They are usually rocks not found in the region.
The glacier pushed big Canadian boulders into Ohio, leaving them behind when the ice melted. The big rocks do not match the local geology. The only Cambrian-aged rocks found in Ohio originated from Canadian outcrops.
The Native-American name for Lake Jackson, located near Tallahassee, Florida, is Lake Okeeheebee, meaning disappearing waters. Local authorities should have kept the original name because there is another Lake Jackson in central Florida, and there is also a Lake Jackson in nearby Georgia. The existence of multiple Lake Jacksons in this region made researching this blog article confusing. I wonder what Native-Americans thought the reason was for the periodic draining of this lake. They probably invented some kind of mythical story. Modern geologists know the cause for the periodic disappearance of this lake. The lake sits on karst terrain where sandy soils prevail. Karst terrain consists of unevenly eroding limestone. Slightly acidic rain causes bedrock to erode, resulting in many underground caverns that often collapse into sinkholes. There are 2 sinkholes underneath Lake Jackson–the Porthole Sink and the Lime Sink. During dry spells when the water table falls, water from Lake Jackson drains into these sinkholes, just like water draining from a bathtub. Plant debris and mud will temporarily block the sinkholes, but eventually most of the lake will drain with the exception of small pools here and there where fish populations survive. The permeable sandy soils allow water to refill the lake following periods of higher rainfall that cause the local water table to rise.
Map and location of Lake Jackson in north Florida. From Wikipedia.Lake Jackson when it is full of water.Aerial photograph of Lake Jackson after its water vanishes. Lake Jackson is surrounded by wet prairie. From the Tallahassee Democrat by Daniel Martinko.
Lake Jackson is 6.2 square miles and averages 6 feet deep when it is full of water, though it is as much as 28 feet deep over the sinkholes. The lake has drained 14 times over the past 200 years, and it is currently in a drained stage. Surprisingly, periodic drainages are good for fishing. The draining reduces populations of the non-native plant hydrilla, and the re-filling stirs up nutrients, increasing food for rebounding fish numbers. Fishermen claim the fishing for largemouth bass, crappie, bluegill and redear sunfish, and bullhead catfish is excellent. The latter species is especially well-adapted for surviving in small pools during drainage phases. Though not mentioned on the internet, I’m sure bowfin, gar, and non-native tilapia thrive as well. Birdwatchers report the presence of herons, egrets, limpkins, eagles, ospreys, ducks, geese, fish crows, and least terns. It’s good habitat for alligators, turtles, and frogs too.
The karst terrain makes it difficult for rivers to flow in this region, and there are 2 rivers that vanish here. The Alapaha River, a tributary of the Suwannee River, simply disappears into the ground, flowing right into a sinkhole, and it emerges miles away. The Santa Fe River also disappears into a sinkhole, also to emerge miles away. Both become subterranean during part of their course. A river flowing into the ground is known as a swallet.
Photo of the Alapaha River where it vanishes into the ground. It re-emerges miles away.Image of where the Santa Fe River vanishes. From a youtube video by Adlai, JN.
An Atlantic Ocean shoreline occurred at the present-day location of the Georgia fall line along an axis from Augusta to Macon to Columbus. Immediately offshore the ocean was shallow, but farther off the coast ocean currents were strong and flowed over a deep channel. This channel originated from a suture or fault where part of the African continent formerly connected to North America before the supercontinent of Pangaea rifted apart. Following sea level rise, ocean currents began flowing over this natural low area about 99 million years ago. Geologists refer to it as the Suwannee Strait during the first 60 million years of its existence and the Gulf Trough from the mid-Eocene to the mid-Miocene. Sea level changes caused the low channel to shift to the northwest, hence the name change. The swift current that flowed over it was part of the clockwise-moving Gulf Stream, an ocean circulation pattern found all the way up the North American east coast. To the south of the Suwannee Strait/Gulf Trough were shallower seas dotted with coral reef islands. During the Oligocene a large island, known as Orange Island, though no oranges grew there yet, emerged above sea level south of the trough. The Gulf Trough was deepest during the late Eocene about 35 million years ago, and geologists think parts of it were 600 feet underwater. During the Miocene sediment washed down from eroding Appalachian Mountains began to fill in the Gulf Trough. In its later years of existence, it was a slow-moving narrower estuary. About 15 million years ago sea level fell and the Gulf Trough existed for a while as an above ground canyon. Today, this canyon is buried deep underneath millions of years of sediment, but there are exposed outcrops where rivers erode through this ancient sediment. However, a relic is visible underwater in the Gulf of Mexico, and it is known as Desoto canyon.
From 99 million years ago to 15 million years ago South Georgia was under deep ocean currents. Geologists refer to this area as the Suwannee Straight and the Gulf Trough. It reached its largest depth about 35 million years ago. The Atlantic Ocean shoreline occurred along the present day fall line. South of this trough was a shallower sea dotted with coral atolls and islands that periodically rose and sankaccording to changing sea levels.
Swift ocean currents carried well oxygenated sea water that supported abundant aquatic life in the Suwannee Strait during the Cretaceous. Monstrous mosasaurs and pliosaurs preyed upon bony fish, some species themselves armed with fangs. Sea turtles and sharks swam over beds of an extinct group of clams known as rudists that came in many different shapes and sizes. Ammonites, extinct cephalopods related to squids and octopi, thrived in Cretaceous seas. Today, most foraminifera are small and measured in millimeters, but oddly enough there were 4-inch-long species of foraminifera living in the Suwannee Strait, though they are one-celled animals related to amoeba.
Rudist clams were abundant in the Suwannee Strait during the Cretaceous era. They came in many different shapes. They went extinct along with the dinosaurs at the end of the Cretaceous.
During the Eocene primitive whales evolved and made the Suwannee Strait their home. The Suwannee Strait and later the Gulf Trough was still rich in fish, mollusks, and other sea life. Fossils in the limestone and shale deposits of Cretaceous through Miocene Age in the region are commonly found wherever erosional processes expose them, and the limestone itself is made of many ancient seashells.
Primitive whales swam alongside dugongs, sharks, bony fish, and turtles in the Gulf Trough during the Eocene.A skeleton of this species was found in Burke County, Georgia.
Notable fossils of Oligocene Age from the Gulf Trough include dugong, nautilus, and rhodoliths. A nearly complete skeleton of a dugong was found in a northwest Florida fuller’s earth mine. Today, just 3 species of nautilus are extant, and these occur in the Pacific and Indian Oceans, but apparently, they were common during the Oligocene in the Gulf Trough. Aturia alabamensis, a 2-foot-long nautilus, likely scavenged or actively hunted crustaceans on the sea bottom. Rhodoliths still exist but were especially abundant in the Gulf Trough during the Oligocene. Rhodoliths are species of red algae that resemble coral and also produce calcium carbonate. Rhodolith fossils are part of large fossiliferous limestone outcrops found in southwest Georgia and are thought to have occurred on the shallower flanks of the Gulf Trough.
Aturia alabamensis. This was a species of nautilus that grew to 2 feet long and was common in the Gulf Trough during the Oligocene.Rhodoliths, red algae that resembles coral, was abundant in the Gulf Trough during the Oligocene. They are still extant.DeSoto Canyon off the Florida coast is the only remnant of the Gulf Trough that hasn’t filled with sediment.
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