Tim Demko
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Tim Demko
@timdemko.xyz
2.8K followers 4.6K following 680 posts
Geologist interested in the energy transition, bicycling, and public service

https://bio.link/timdemko

https://orcid.org/0000-0002-9125-0907

https://www.semanticscholar.org/author/Timothy-Michael-Demko/15743754
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timdemko.xyz
After liking this post and reading the linked paper, I was keen to see if I'm missing these features in outcrops. Tooling around some basalt flows along Kona Coast in Hawaii today (Shoreline Park, just west of Kealakekua)...well, yep! Will be keeping my eye peeled for these in older flows in AZ!
Photo of the an outcrop of dark gray vesicular basalt, exhibiting fracture patterns of two natural explosion structures. The structures look like cavities surrounded by radially-oriented fractures. My sandaled foot is also shown, for scale.
October 6, 2025 at 6:48 AM
timdemko.xyz
Any self-respecting ichnologist despises fish because they can make the most frustratingly uninterpretable traces.
www.livescience.com/63627-puffer...
Photo of a Japanese pufferfish posing defiantly in front of its needlessly complicated and beautiful sea floor sand sculpture. Asshole!
October 3, 2025 at 10:11 PM
timdemko.xyz
Here is the response from the event on my RaspberryShake 4D seismometer near Phoenix, AZ USA
Seismogram of 7.4 magnitude earthquake off Kamchatka as measured on a RaspberryShake 4D seismometer near Phoenix, AZ USA. The figure is a composite diagram with 3 parts: an upper record of the seismic wave amplitude over time, a middle part showing the frequency spectrum over time, and a lower graph of the complete frequency spectrum over the time interval of the upper two parts
September 13, 2025 at 4:18 AM
timdemko.xyz
After poking around and finding the base of the flow, the story became much richer: the basalt had flowed over some eolian dunes which sourced the water for the hydrothermal system. The sand might have accumulated as obstacle dunes around a bedrock hill, then buried by the flow in a valley. (2/2)
Outcrop photo of Miocene eolian dune deposits overlain by vesicular basalt. The dune deposits are light orange-brown and characterized by wind ripple/translatent (pin-stripe) laminations, and the basalt is very dark reddish brown. the contact is very sharp. There is ddesert vegetation, including saguaro cacti visible in the background. Outcrop photo of Miocene eolian dune deposits overlain by vesicular basalt. The dune deposits are light orange-brown and characterized by wind ripple/translatent (pin-stripe) laminations, and the basalt is very dark reddish brown. The basalt exhibits intense fracturing, with light colored fracture fills. the contact is very sharp. There is an archaeologist (Madi Whalen) for scale. Outcrop photo of Miocene eolian dune deposits overlain by vesicular basalt. The dune deposits are light orange-brown and characterized by wind ripple/translatent (pin-stripe) laminations, and the basalt is very dark reddish brown. The basalt exhibits intense fracturing, with light colored fracture fills. There is an archaeologist (Madi Whalen) for scale. Outcrop photo of Miocene eolian dune deposits overlain by vesicular basalt. The dune deposits are light orange-brown and characterized by wind ripple/translatent (pin-stripe) laminations, and the basalt is very dark reddish brown. The basalt exhibits intense fracturing, especially at the contact with the underlying sandstone, with light colored fracture fills. The units and the contact are offset by a small vertical fault.
September 9, 2025 at 3:57 AM
timdemko.xyz
Saw these outcrops of the mineralized, brecciated top of a Miocene basalt flow today, evidence of an epithermal hydrothermal system. This indicates the interactions of mineralized, boiling water, explosively flashing to steam, breaking up the rock, depositing minerals in fractures and cavities (1/2)
Outcrop photo of brecciated basalt, with dark pieces of vesicular basalt separated by lighter interstices, fracture fills, and mineralized cavities. The photo is of a vertical profile of the top of a basalt flow. There is a cell phpne for scale. Outcrop photo of brecciated basalt, with dark pieces of vesicular basalt separated by lighter interstices, fracture fills, and mineralized cavities. The photo is looking down onto the top of a basalt flow. There is a boot for scale. Outcrop photo of brecciated basalt, with dark pieces of vesicular basalt separated by lighter interstices, fracture fills, and mineralized cavities. The photo is looking down onto the top of a basalt flow. There is a boot for scale. Outcrop photo of brecciated basalt, with dark pieces of vesicular basalt separated by lighter interstices, fracture fills, and mineralized cavities. The photo is looking down onto the top of a basalt flow. There is a boot for scale.
September 9, 2025 at 3:57 AM
timdemko.xyz
Joe's post reminded me of this piece of artwork given to me me by the artist, William "Rockman" Gooder from Duluth, MN. William would come to my office with collections of stones he chose from the gravel beaches of Lake Superior for his artwork, asking me to to tell him the story of each one. (1/2)
Framed artwork made of multicolored rocks and tan sand from the shores of Lake Superior, MN. Artwork by William Gooder: https://www.williamgooder.com/
August 25, 2025 at 4:38 AM
timdemko.xyz
MEGAQUAKE! 8.7 off of Kamchatka. Here is the response on my RaspberryShake 4D in Phoenix, AZ USA #earthquake #RaspberryShake
Seismograph showing response from a magnitude 8.7 mega earthquake off of the southern Kamchatka peninsulaon a RaspberryShake 4D seismometer in Phoenix, AZ USA. The figure has three graphical sections: 1) a time series of the amplitude of vibrations in meters/second over about 50 minutes, 2) a time series of the frequency response over the same time interval, and 3) an amplitude versus frequency diagram showing a peak frequency of about 0.25 Hertz
July 30, 2025 at 12:42 AM
timdemko.xyz
Cover of DC Comics Unexpected #157, showing panels from stories "Who Will Kill Gigantus" with a theropod dinosaur chewing a battle tank on the steps of the Capitol, "The Abominable Snowman" with a giant yeti about to throw an enormous snowball at someone viewing it's tracks, and "The Thing from the Dead Letter Office" with a monster peaking into a window in a room with a cowering woman.
July 20, 2025 at 2:18 AM
timdemko.xyz
Here are some highlights from deep red Surprise, Arizona. There were several hundred folks lining about 4 blocks, both sides of the highway. Well behaved, except for a few drive-by hecklers. The group was very diverse, happy, and fired up! Kudos to the No Kings organizers!
Protest sign that reads "Gestapo 1933, ICE 2025" Protest in Suprise, AZ; people holding protest signs: "Nobody is illegal on stolen land", "rebellion against tyrants is obedience to God - Benjamin Franklin", "Respect the Constitution, uphold the rule of law", "One wing for justice, one wing for judgement" Protest sign: "Does this ass (photo of Trump) make my country look small?" Protest sign: painting of the Statue of Liberty covering her eyes
June 15, 2025 at 4:56 PM
timdemko.xyz
Thought of this photo right away: left it all in the field! Clockwise from left: Brian Bodenbender, me, Mark Uhen: Shell, WY, July 2004. We survived.
Three dirty, exhausted, and happy geologists, sleeping sacked out in camp chairs and on the ground.
May 15, 2025 at 10:56 PM
timdemko.xyz
Artificial Intelligence when I was a kid:
See 'N Say talking learning toy, circa 1964. My dialect comes from this toy and Myron Cope (...on sports) sportscaster from KDKA TV in Pittsburgh. Yoy.
May 6, 2025 at 4:18 AM
timdemko.xyz
Got an exclusive preview of the Auburn University Geo Explorer Lab, a 37 foot RV mobile learning lab under construction that will introduce students, teachers, and community partners to the breadth of geoscience approaches to science and social studies learning.
The Auburn University Geosciences Department "Geo Bus", or mobile Geo Explorer Lab. It will bring science and technology experiences to students, teachers, and other community members all across the State of Alabama. It is a converted 37 foot RV that will house educational science and technology equipment and learning stations. The Auburn University Geosciences Department mobile Geo Explorer Lab Microscopes and VR headsets in the Geo Explorer Lab Topography learning lab that uses molding sand, 3D scanner, and LCD projector so that learners can understand elevation contours.
April 27, 2025 at 2:58 PM
timdemko.xyz
What is the coolest shot in movies?

#Filmsky
Final scene from the movie Planet of the Apes, when Taylor realizes that he is actually on future Earth, looking at the ruins of the Statue of Liberty.
February 15, 2025 at 5:07 AM
timdemko.xyz
We did have a President who felt the same way: www.americanrhetoric.com/speeches/jim...
In a nation that was proud of hard work, strong families, close-knit communities, and our faith in God, too many of us now tend to worship self-indulgence and consumption. Human identity is no longer defined by what one does, but by what one owns. But we’ve discovered that owning things and consuming things does not satisfy our longing for meaning. We’ve learned that piling up material goods cannot fill the emptiness of lives which have no confidence or purpose. The symptoms of this crisis of the American spirit are all around us. For the first time in the history of our country a majority of our people believe that the next five years will be worse than the past five years. Two-thirds of our people do not even vote.
January 19, 2025 at 6:07 PM
timdemko.xyz
< February 19 FTW >

We were both kissed by a rose on the grey...

This is fun, a timeline cleanse if you will. Who is your celebrity Birthday Twin, born on the same day as you?

Reply with a pic or gif
Singer Seal, born on February 19, 1963
January 13, 2025 at 1:35 AM
timdemko.xyz
These are crater-fill sediments in the Oligo-Miocene Hopi Buttes Volcanic Field. Volcanic rocks and volcanoclastic sediments interfinger with Bidahochi Formation. This succession preserves interaction between extrusive and intrusive igneous activity and a pre-Grand Canyon fluvial-lacustrine system.⚒️
Google Maps street-view image of crater-fill sediments. Google Maps street-view image of crater-fill sediments. Google Maps street-view image of crater-fill sediments. chunk of the Winslow 30' x 60' geologic map, Billingsley, G.H., Block, D., and Hiza Redsteer, M., 2013, Geologic map of the Winslow 30’ × 60’ quadrangle, Coconino and Navajo Counties, northern Arizona: U.S. Geological Survey Scientific Investigations Map 3247, pamphlet 25 p., 3 sheets, scale 1:50,000, and GIS data, https://pubs.usgs.gov/sim/3247/
January 9, 2025 at 7:28 PM
timdemko.xyz
Saw this exposure of an extensional detachment fault today, capped by Quaternary sediments across an angular unconformity. Precambrian igneous rocks form the footwall, while Miocene volcanoclastics and basalt are in the hanging wall. The detachment is a fault zone, here expressed as 2 normal faults.
Wide-angle photo of an outcrop of an extentional detachment, expressed as two normal faults deforming Precambrian granite and Miocene volcanoclastics and basalt. This succession is overlain by Quaternary fluvial sediments across an angualr unconformity. The rocks and light red and gray, and there is blue sky and white streaky clouds in the background., as well as scrubby desert vegetation on the top of the outcrop. Closer view photo of an outcrop of an extentional detachment, expressed as two normal faults deforming Precambrian granite and Miocene volcanoclastics and basalt. This succession is overlain by Quaternary fluvial sediments across an angualr unconformity. The rocks and light red and gray, and there is blue sky and white streaky clouds in the background., as well as scrubby desert vegetation on the top of the outcrop. There is a gold pencil on the outcrop for scale. Interpreted closer view photo of an outcrop of an extensional detachment, expressed as two normal faults deforming Precambrian granite and Miocene volcanoclastics and basalt. This succession is overlain by Quaternary fluvial sediments across an angualr unconformity. The rocks and light red and gray, and there is blue sky and white streaky clouds in the background., as well as scrubby desert vegetation on the top of the outcrop. There is a gold pencil on the outcrop for scale. The unconformity is outlined with a red line, while the faults are outlined in black, the rock units are labeled and the sense of movement of the faults is shown with arrows.
January 7, 2025 at 4:57 AM
timdemko.xyz
Some great geomorphic and sedimentologic features seen while out mapping igneous/metamorphic rocks: feeder channels to the apex of this alluvial fan incised, left behind a flight of boulder-levee-lined terraces. Boulders were stranded along the channel edges by debris flows coming down the drainage.
Photo of the apex of an alluvial fan, looking down from a hill above. The feeder channels of the fan have been incised, leaving boulder levee-lined flights of terraces. It is a desert landscape, with cholla and saguaro cacti and palo verde trees. The foothills of mountains are in the background.
December 14, 2024 at 10:30 PM
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From a reply to a repost: didn't include because it doesn't have a scale. The contact here is much more complicated, but the big white crystals near the bottom of the pegmatite outcrop here are giant (1 m long) spodumene laths. You can spot other spodumene laths throughout the main pegmatite.
Outcrop photo of a light colored pegmatite intruded into darker schist. There is a smaller pegmatite body that offshoots the main body. There are large lath-like crystals of spodumene intergrown with quartz, feldspar, and muscovite.
December 14, 2024 at 6:58 PM
timdemko.xyz
Here is another nearby outcrop that I didn't include because it doesn't have a scale. The contact is much more complicated, but the big white crystals near the bottom of the pegmatite outcrop here are giant (1 m long) spodumene laths. You can spot other spodumene laths throughout the main pegmatite.
Outcrop photo of a light colored pegmatite intruded into darker schist. There is a smaller pegmatite body that offshoots the main body. There are large lath-like crystals of spodumene intergrown with quartz, feldspar, and muscovite.
December 14, 2024 at 4:14 AM
timdemko.xyz
Nice example of an igneous intrusive contact between a light colored pegmatite and a darker schist in central Arizona USA. The contact is sharp and sinuous, and the pegmatite shows little evidence of a finer-crystalline chilled margin. The pegmatite has abundant spodumene, a lithium-bearing mineral.
Outcrop photo of a light colored pegmatite intruded into darker schist. The contact is sinuous and sharp. There are some bunch grasses growing on the outcrop and a small scraggly tree at the top. Photo of an outcrop of a the intrusive contact between a light colored pegmatite and darker schist. The contact is sharp and shows little alteration and the pegmatite shows little evidence of a finer crystalline chilled margin. There is a mechanical pencil for scale. Photo of minerals in a pegmatite intrusion. There is very light gray quartz intergrown with white spodumene. There is a mechanical pencil for scale.
December 14, 2024 at 3:45 AM
timdemko.xyz
Field work in the White Tank Mountains in central Arizona USA: great igneous relationships between screens or xenoliths of Proterozoic schist and a Cretaceous/Paleogene granite! There are also some younger pegmatite veins that cut both. This is also the lower plate of a metamorphic core complex.
Photo of an outcrop of light brownish red schist cut by lighter granitic dikes. Shadow of the photographer for scale in the lower left corner. Photo of an outcrop of screen or large xenolith of light brownish red schist surrounded by a lighter granite and cut by lighter granitic dikes. Photo of an outcrop of a light colored granitic dike cutting a darker gray schist. The foliation of the schist is vertical and cut at a right angle by the dike. The dike has two bands, an equigranular granite and coarsely crystalline pegmatite. There is a brass pen for scale.
December 7, 2024 at 5:12 AM
timdemko.xyz
Found this impressive packrat midden in the Vulture Mountains of central Arizona USA. Packrats construct their middens by obsessively collecting vegetation debris and other objects within about 100 m of the midden site. They only get water from eating vegetation, so their urine is very concentrated
Photo of a packrat midden, a collection of sticks, cactus pads and spines, and other plant debris. The midden is stuated in the crevice and overhang of agray to light red rock outcrop. There is a clump of dark amberat (solidified packrat urine and feces) in the upper center of the midden, adhered to the rock.
December 5, 2024 at 3:10 AM
timdemko.xyz
A nice igneous intrusive relationship between a dark reddish brown andesite breccia and a light red rhyolite porphyry with dark mafic inclusions (left). This outcrop is part of the Vulture Mountains (right) volcanic center in central Arizona USA. These units were emplaced in the Miocene, ~20 Mya.
Outcrop photo showing a dark reddish brown andesite breccia intruded by a light red rhyolite porphyry. The contact is jagged and irregular, and the porphyry contains some dark mafic xenoliths. Photo of the Vulture Peak in the Vulture Mountains of central Arizona USA. These mountains consist of Miocene volcanic rocks and associated intrusions. There is desert vegetation in the foreground, including saguaro cacti and palm verde trees.
December 4, 2024 at 3:00 AM
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"spoken-word-slam-poetry"...I knew someone would get the bit, eventually! Now, finally, you all know.
Screenshot from results of label scanner: "bluesky-elder" from Skywatch Blue/Anti-Alf Aktion, "he" from Pronouns Labeling System, "spoken-word-slam-poetry" from The Cave of Trophonius, "geology" from STEM Laberler, "sedimentology" from STEM Labeler, "stratigraphy" from STEM Labeler
December 3, 2024 at 2:51 AM