Tuesday, September 29, 2020

Utah's Recent Volcanic Legacy

Utah is known for a lot of geological marvels, however one of them that isn't often talked about, or even realized that we have, are volcanoes. And active ones at that, with the most recent volcanic eruption dating around 660 years ago. Utah's history is deep and varied, and although there is evidence for numerous volcanic eruptions through time with volcanoes buried deep in our geological past, I am only going to focus on some of the most prominent and recent volcanic eruptions that you can visit and see the evidence of today.

Geologic Background

The reason that Utah has so many active volcanoes is because of Plate Tectonics, the process that produces mountains, earthquakes, islands, volcanoes, among many other features across the globe. It all started many millions of years ago (at least 40) as the plate off the western coast of North America, the Farallon Plate, was subducting (going beneath) the North American Plate. This subduction was due to the Farallon Plate moving towards the North American Plate, and since the oceanic plate was denser, it got forced downward. As the plates pushed against each other, besides just riding on top of the Farallon Plate, the North American plate also ended up being compressed, or squeezed, like a sponge. 

Illustration of the plate tectonics of the west coast of North America with the Farallon Plate subducting beneath North America. Image courtesy of the NPS

Over the course of the last 40 million years, or so, the Farallon Plate was eventually subducted almost entirely beneath the North American plate. This rather hot plate, forced the area known as the Colorado Plateau vertically upwards, creating features such as the Grand Canyon, and Zion National Park. However, once the subduction zone on the west coast was no longer present, the compressive force was no longer present either. This resulted in the western part of the North American plate being now allowed to expand, and like a released sponge, it did expand. This expansion is what produced the Basin & Range Province, which is a series of alternating linear mountain ranges and valleys. 

Evolution of the western coast of North America going from a subduction zone to a transform plate boundary causing the formation of the extensional Basin & Range Province. Images courtesy of the NPS.  

Besides just creating the alternating mountains and valleys, the expansion of the Basin & Range Province produced another effect, a thinning of the crust. As the crust thins, the liquid mantle gets closer to the surface. And since it is closer to the surface, there are times when the hot liquid mantle is able to melt the overriding crustal rocks, forming volcanoes. 

The thinning of the crust causes the upper mantle (asthenosphere) to rise up and melt the overlying rocks producing volcanoes. Image courtesy of the NPS and Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest, by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015.

And that is what has been produced in Utah, a series of volcanoes that align along the eastern edge of the Basin and Range Province. The Basin & Range province essentially ends with the Wasatch Mountain Range to the east, curving westward down through St. George in southern Utah. This line is  paralleled by the line of active, or recently active, volcanoes in Utah, seen in the map below. By definition, an "active" volcano is one that has erupted within the last 10,000 years. We will go through them from north to south. 

Map of the most recent, active volcanoes in Utah. 

1. Fumarole Butte
Photo of Fumarole Butte I took while flying over it from Salt Lake City to Las Vegas.

Fumarole Butte is located just to the northwest of Delta, Utah. It is considered on of the five "subfields" of the Black Rock Desert volcanic field, and it is the oldest of the five subfields. Fumarole Butte was active sporadically from 6.1 to 0.3 million years ago. The most obvious feature of Fumarole Butte is the shield volcano seen above that dates to about 0.9 million years old. A shield volcano is a volcano made up of mostly basaltic rocks, which forms from thin and runny lava that has a low silica (quartz) content. They are also very dark grey to black in color. The most common shield volcanoes in the US are the Hawaiian Islands. Another famous feature of the region is Topaz Mountain, a rhyolite dome with abundant topaz deposits. Rhyolite is on the opposite end of the viscosity spectrum from basalt, where the lava is thick, with a high silica content, and is usually very light in color.

2. Pahvant Butte
Pahvant Butte. Image courtesy of Desert Survivor

Moving our way south, our next volcanic feature is the Pahvant Butte, which is a type of volcano known as a tuff cone. Per National Geographic:
"When heated rapidly by lava, water flashes to steam and expands violently, fragmenting huge amounts of lava into plumes of very fine grains of ash. This ash falls around the volcanic vent, creating an ash cone. Over time, the ash weathers into a rock known as tuff."
Pahvant Butte is located within the youngest of the five Black Rock Desert subfields, Ice Springs. Erupting ~15,500 years ago, Pahvant Butte started erupting during the time of Lake Bonneville, a vast Ice Age lake that covered much of Utah and Nevada. The volcano quickly breached the surface of the lake, rising to a total of 740 feet (about 400 feet above the highest lake levels). Several shorelines were eroded into the volcano at the time including one that called the "Lace Curtain", which is a vertical cut shoreline cliff, which exposes tuff that was cemented by the ground water producing an intricate lacy pattern.  

3. Ice Springs Volcano
The sign here led me to believe that the volcano was called Red Dome, however that is just the mining operation that uses the scoria from the cinder cone.

Google aerial photo of the Ice Springs Lava Flow. 

The Ice Springs volcano and lava flow is easily one of the most recognizable features in Utah on Google Earth. It is a strong black smear on the landscape in an otherwise brown and green landscape located just west of the town of Fillmore. I had visited the volcano on a drive home. I had frequently driven fairly close to this area but never actually stopped before. It was a lot of fun just to check out some of the volcanic debris.

View of the cinder cone (left) and the lava flow driving up. 

Closer up view of the lava flow

Close up of the cinder cone.

Inside the cinder cone. 

A piece of scoria from the Ice Springs volcanic eruption.

The Ice Springs volcano and lava flow is the youngest of the Black Rock Desert subfields and the youngest of all of the lava flows in all of Utah, dating to about 660 years ago (~1360 CE). The volcano is a cinder cone, which is a volcano formed from the eruption of "cinders", also known as scoria, dark black basaltic rocks full of air holes. The lava erupts out of the crater and solidifies in the air, piling up alongside the vent. Eventually these "cinders" build up into a cone shape. The area also contains a basaltic lava flow. 

4. Tabernacle Hill Lava Tubes
Also part of the Ice Springs subfield, since the Tabernacle Hill Lava Tubes were distinct enough and located a little bit further south than the main Ice Springs volcano, I am listing it separately. The Tabernacle Hill Lava Tubes erupted ~14,500 years ago and are located to the west of Meadow, Utah. They consist primarily of basalt.  

The Tabernacle Hill Lava Tubes. Image courtesy of Utah's Adventure Family.

A lava tube is formed during a volcanic eruption when you have a flowing river of lava. The surface of that river is in contact with the air and slowly starts to solidify. Eventually the lava river crusts over, insulating the lava in the river. This allows for the lava river to keep flowing and eventually when the volcano peters out, the lava flows out leaving the solidified tube behind. Lava tubes are predominantly made out of basaltic rocks, because the higher viscosity rhyolitic (high silica) lava can't flow fast enough to produce the lava rivers. Within the Tabernacle Hill eruption there is also a central crater still present that once held a lava lake. 

5. Markagunt Plateau volcanic field
Lava flows of the Markagunt plateau (Makagunt means "highland of trees" in the Paiute language). Image courtesy of the USRA

The Markagunt Plateau volcanic field is a vast field with many volcanic eruptions across it primarily composed of basaltic rocks and scoria. It is located east of Cedar City, Utah and butts up against the Cedar Breaks National Monument. The area of the volcanic field exceeds 1,000 square miles and was active from 5.3 million years ago to less than 10,000 years ago. Overall, there were 40 to 50 one-off cinder cone eruptions that formed over three distinct periods of time: 5.3 to 2.8 million years ago, 1 to 0.5 million years ago, and less than 0.5 million years ago. The youngest lava flows are estimated to be around 900 years old, based on the ages of the oldest trees on the flows. This agrees with a Southern Paiute legend, whom arrived in the area around 1,000 years ago, about the ejection of fiery rocks and molten lava flows (Palmer, 1957). 

6. Santa Clara Volcano

The Santa Clara cinder cone volcano. Image courtesy of Mapio.

The Santa Clara volcano is a cinder cone located to the north of the city of St. George, Utah, and is one of the southernmost volcanoes within Utah. Within the area are two cinder cones and a lava flow that flowed 16 km south down into Snow Canyon. The associated basaltic lava flow has been dated at ~27,000 years old. This lava flow is often touted as one of the Colorado Plateau's youngest lava flows, however the dates of many in the Black Rock Desert and Markagunt Plateau have been dated to be vastly younger. 
Palmer W R, 1957. Why the North Star Stands Still and other Indian legends. Englewood Cliffs, New Jersey: Prentice-Hall, 158 p.
Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest, by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015

Sunday, September 13, 2020

Geologic State Symbols Across America - Georgia

 The next state up for the Geological State Symbols Across America is:


You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along).

                                                                             Year Established
State Mineral: Staurolite                                                1976
State Gemstone: Quartz                                                 1976
State Fossil: Shark Tooth                                                1976

I also have some Geology of the National Parks Through Pictures that I have done for Georgia previously. These include:


State Mineral: Staurolite
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating staurolite as the official State mineral...  
Whereas, Georgia has a wealth of minerals and gemstones; and  
Whereas, staurolite is a mineral found in old crystalline rocks and is particularly well known and abundant in north Georgia; and  
Whereas, staurolite crystals are known mostly as “Fairy Crosses” or “Fairy Stones”, and generations after generations have collected them for good luck charms; ...  
Whereas, the importance of Georgia’s minerals to the industrial growth and heritage of this State should be appropriately recognized.  
Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made:
(1) Staurolite is designated as the State of Georgia’s official mineral.... Approved May 18, 1976.
An example of a staurolite crystal showing the 60-degree penetrating twin cross. 
Image from iRocks.com

Staurolite is a metamorphic mineral, meaning that it is formed from the increased heat and pressures that form metamorphic rocks, like gneiss or schist. Staurolite is part of the silicate group of minerals with a chemical formula of (Fe,Mg)2Al9Si4O23(OH). The mineral is usually brown to black in color with a vitreous (glassy) luster. It can be found in transparent varieties, however the most common variety is opaque. It is also rather hard, 7 to 7.5 on the Mohs Hardness Scale, meaning that is is on par with quartz, and resistant to weathering so it will often erode out of its host rock intact, ending up within sedimentary deposits of local rivers. The crystals of staurolite are what truly make it a unique mineral though. Commonly found as six-sided, elongated crystals, the most striking feature are the penetrating twinned crystals creating an "X" shape (60-degree angle crosses) or, less frequently, a "+" shaped cross (90-degree angle crosses). Even the name of "staurolite" comes from the Greek word for cross "stauros". Because of these twinned crystals, staurolite is sometimes referred to a "fairy crosses", because of the legend that at the death of Christ, the local fairies cried tears that crystallized into cross-shaped crystals. Within the US, there are a high abundance of staurolite crystals found at Fairy Stone State Park, Virginia, with the name based on the legend. There are relatively few actual uses for staurolite, because of the rarity of the mineral compared to other options. It was once used as an abrasive because of it's extreme durability, but other, cheaper sources are now used. The most common use now is as a decorative item or as jewelry due to its "mystical" properties and its cross-shape. 

The geological regions of Georgia. Image from the Georgia Encyclopedia.

Within the state of Georgia, there are only a handful of locations and rock formations that contain staurolite. The state itself can be broken into five distinct geological regions, as seen on the map to the left. The Coastal Plain, Valley & Ridge, and Appalachian Plateau Regions are dominated by sedimentary rocks, and are therefore not where you would generally find staurolite. The Piedmont and Blue Ridge Regions though, are heavily rich in metamorphic and igneous rocks. In fact the counties within the north-central region including Cherokee, Fannin, Hart, Upson, and Warren Counties are your best bets for finding staurolite crystals (geologic map below). Within the Piedmont and Blue Ridge regions, there are certain formations that are the best ones for staurolites. The Great Smokey Group is a Late Proterozoic (~600-700 million years old) rock group that can be divided up into several distinct rock formations. Of which, the Copperhill, Dean, and Hughes Gap Formations all contain staurolite schist, staurolite-mica schist, and/or staurolite-garnet-mica schist interbedded with other metamorphic rocks. The Hughes Gap Formation is noted as having a few "spongy or stringy masses of staurolite" within staurolite zones. Since staurolite is resistant to erosion, the crystals have a habit or eroding out of the rock and accumulating on the surface or within nearby stream beds. The other major contributor of Georgia staurolites is the Mineral Bluff Formation, another Late Proterozoic metamorphic assemblage that includes a minor amounts of staurolite schist interbedded with other metamorphic rocks. 

A highlight of the metamorphic rocks within northern Georgia. Image from the Georgia Geological Society

Notable occurrences of staurolites from the Mineral Bluff Formation include the J.M. Spear farm near Ball Ground in Cherokee County. Notable occurrences of staurolites from the Hughes Gap and Dean Formations include the J. Fred Hackney farm near Blue Ridge and the E.D. Richars property near Mineral Bluff in Fannin County. Other notable localities include the towns of Royston, Thomaston, and Norwood. Detailed location data can be found within the Minerals of Georgia book on page 111

State Gemstone: Quartz
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating ... quartz as the official State gem....  
Whereas, Georgia has a wealth of minerals and gemstones; ... and
Whereas, quartz is the second most abundant mineral on Earth, and Georgia is blessed with a great deal of it in a wide variety of colors; and  
Whereas, quartz is the amethyst that has been most used in jewelry, and clear quartz when faceted resembles diamond; and  
Whereas, the importance of Georgia’s minerals to the industrial growth and heritage of this State should be appropriately recognized.  
Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made: ...
(3) Quartz is designated as the State of Georgia’s official gem. Approved May 18, 1976.
An example of a quartz crystal from Cold Water Creek, Rock Branch, Georgia.
Image from iRocks.com.

Quartz is one of the most common minerals on Earth, primarily due to its simple structure and chemical formula, SiO2. Quartz also has an extremely high hardness, 7 on Mohs hardness scale, meaning that it doesn't scratch very easily and therefore does not break down easily. As the rocks on Earth are slowly eroded over time, most of the other minerals will break down into clay while quartz grains will generally just gets smaller and smaller. The result is that most beach sand is composed of quartz that has a slight hematite (rust) stain to it to give the sand grains their slight yellowish color. Although quartz is a simple mineral, it can come in a variety of colors depending on what type of impurities are present in the crystal structure; pure quartz crystal is clear, milky quartz is white, smoky quartz is grey, amethyst is purple quartz, citrine is yellow quartz, rose quartz is pink, as well as some other colors and varieties. Quartz does not have any cleavage, meaning that when it breaks it doesn't form along perfect surfaces. Instead as the quartz crystals grow, individual mineral molecules of quartz are added to the outside of the crystal from water rich in dissolved SiO2 or mineral melt (liquid rock like lava or magma). 

Here is a map of all of the known quartz crystal discovery locations. These include every possible range of colors in quartz from citrine to amethyst. Map courtesy of mindat.org.

The mineral quartz is pervasive throughout all crustal rocks, especially in coastal states like Georgia, since quartz is the primary component of sand. However, when designating "quartz" as the state gemstone, the government specifically mentioned amethyst (which is purple quartz) and "clear quartz when faceted resembles diamonds" (also known as quartz crystal). Like staurolite above, crystals of amethyst and clear quartz are generally only found in the northern half of Georgia, within the Piedmont and Blue Ridge Regions (as per the map to the left). One of the most publicized locations for mining amethyst is the Jackson's Crossroads Amethyst Mine located to the east of Athens. The mine is located with a rock known as a metadacite, which is a metmorphosed dacite. Dacite is a volcanic rock with a fairly high silica (quartz) content, located between rhyolite and andesite on the felsic-mafic scale. Being a volcanic rock, there are many holes (termed vugs) within the rock, allowing for the precipitation of quartz crystals over time. It is within these vugs that the amethyst is found. Although Jackson's Crossroads is a private mine, they do offer opportunities for public digging. Although the main attraction here are amethysts, clear quartz crystals can also be found in abundance within these sorts of mines. Besides just the metadacite, quartz crystals (including amethyst) can be found in a wide variety of the rocks in northern Georgia including gneiss, another metamorphic rock. These gneisses, formed from granite or shale, also had many vugs within them. Over time the quartz/silica within the gneiss got leached out by groundwater and started to precipitate within the vugs. As the mineral crystallized, it formed a consistent pattern and shape, which is the quartz crustal we all know and love. When the quartz crystals are found intact within the vugs, these are what are known as geodes. Other locations for amethyst crystals include Warrenton within some granitic gneiss, the Coldwater Creek area and the Chapman Mica Mine, both in Elbert County, and near Tate City in Pickens County. While amethyst is generally not widely available, other varieties of quartz, especially clear quartz crystals, can be found all over the northern half of Georgia as seen in the quartz crystal location map above.

State Fossil: Shark Tooth
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating ... the shark tooth as the official State fossil...; and
Whereas, the shark tooth is a relatively common fossil in Georgia and in fossil form can be traced back 375,000,000 years; and

Whereas, the teeth are especially prized for fossil collectors and range in color from the more common blacks and grays to white, brown, blue and reddish brown; ...

Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made: ...

(2) The shark tooth is designated as the State of Georgia’s official fossil.... Approved May 18, 1976.

A variety of fossil shark teeth, representing the multiple possible colors. Image from the Florida Museum by Jeff Gage.

Within the fossil record, sharks have a fairly long history. Scientists have fossil shark material that dates back over 420 million years ago during the Silurian. However, there is very little of a shark that is typically preserved. In general, the skeleton of sharks, as well as all chondrichthyans, which includes rays and skates, are made up of cartilage. Cartilage is a material that breaks down very quickly and hardly is ever fossilized. Fossilization is the process where organic material is turned into stone by a one-to-one replacement of the organic material with more permanent minerals such as silica (quartz) or calcite. The fossilization, or permineralization, process causes the teeth to be a wide variety of colors depending on the elements within the water that replaced the organic materials. Even a little of something, such as iron, can turn a normally white item into a very rich red color. Cartilage, however, breaks down very quickly and so the fossilization process does not typically occur. However, there are several features of a shark that can be preserved with the teeth being the most common. Shark teeth are made up of dentin, a material harder and denser than bone, and covered with an enamel shell. On top of that, sharks typically go through tens of thousands of teeth a year. So one shark could potentially produce 50,000 teeth over its lifetime. Fossilization potential also exists for the denser cartilaginous sections of the shark skeleton as well, just not as highly as the teeth. These include the dense core of the vertebrae, parts of the jaw, the rostral (nose) node, and on some sharks, the spines. Dermal denticles are another fossilization potential. They are tiny pieces of bone that are scales on the outer surface of the shark skin. 

Teeth from the shark Hemipristis serra showing the wide variety of teeth even within one shark specimen. Image from fossilguy.com.

Shark teeth, however, can tell us a lot and not very much about the shark. Shark teeth are amazingly varied, even within a shark. Look at the picture above to the right. The teeth can vary in males to females, in juveniles to adults, in the top and bottom jaws, as well as where they are located within the jaw. Therefore, by just finding the teeth it is nearly impossible to determine how many species once existed because the teeth aren't attached to anything anymore (the jaws tending to all degraded away), or even what species an individual tooth came from. Loose teeth are also very difficult to date. The only real indicator of the age of a shark tooth is to find the sedimentary rock bed that it came from and date that. The one exception to that rule is the shark Carcharocles megalodon, more commonly referred to as just Megalodon. Due to the extreme size of their teeth, they are actually fairly easy to identify. However, a full jaw of Megalodon teeth has never actually been discovered and all representations of them are completely made up by people who think what they might have looked like. In general, shark teeth can be a fairly abundant and cool fossil collectible, depending on the local fossil collecting regulations. Sharks are vertebrates and therefore would fall under any vertebrate fossil collecting restrictions. 

Map of Georgia Counties with fossils found within them. Rock age range of the Coastal Plain ranges from Cretaceous (grey) to Holocene/Modern (tan). Map from Georgiafossils.com.

Unlike the state mineral and the state gemstone, which are both primarily found within metamorphic or igneous rocks, fossil shark teeth are found primarily within sedimentary rocks. And the best place to locate them would be the southern region of the state known as the Coastal Plain (according to the map above). The rocks in the Coastal Plain Region range from Cretaceous to the Holocene/modern day. The rock units that fossil shark teeth are found in is generally marine limestone, however they have been found in other rocks and materials as well including younger unconsolidated sediments (not compressed and cemented into rocks yet). One location that has turned up an abundance of fossil shark teeth are the man made islands along the southern Savannah River. These islands are composed of dredged sediment from the Savannah River, so although the islands contain an abundance of fossils, the material isn't much use scientifically since they had been heavily transported from their primary site of deposition 19 million years of deposits mixed together. Oligocene fossil shark teeth have been found further inland in the limestone deposits of the Ocmulgee Formation, located within the Oaky Woods Wildlife Managment Area. Finally, some of the oldest shark teeth in Georgia can be found within the Cretaceous age Eutaw Formation alongside pterosaur fossils and the Blufftown and overlying Cusseta Formations. These teeth largely represent an extinct species of goblin shark, where the shark has essentially a pronounced overbite. Besides these there are likely thousands of individual instances of shark fossils found across the southern half of Georgia and it is no wonder why the shark tooth was decided upon as the state fossil. However, as I stated before, sharks are vertebrates and often fall under strict collecting rules so before you go out collecting fossils, make sure you are aware of the local rules and regulations and are following them appropriately. 


Thursday, September 10, 2020

Drunk on Geology

 Hello friends, family, and random internet strangers,

I have been working hard on a new website that I think followers of The Geology P.A.G.E. here would enjoy and that's DrunkOnGeology.com. It has all the great geology based wines and beers that used to be on this site plus more. Within the website I go into the geological background of a geology themed liquor and peal apart why the alcohol may have been named that and how it relates to the geology of the region where it is from or how it relates to geology in general. It is a lot of fun and I think you will get a lot of information out of it. So go on over and check it out!