Post has attachment
Folded Grenville Marble

When placed under stress, some materials are stiff, and others behave like putty. At high Temperature, even rocks show these properties. Carbonate rocks like marble are extremely susceptible to recrystallization, so are folded quite easily, like the black and white layered rock pictured here. Silicate rocks, however, are a good deal more resistant to getting pushed around. The dark black rock in the upper left corner is experiencing the same stress as the marble, but it is acting as a solid block and remains undeformed, floating around in a squishy mess of putty.

#FridayFold #GeologicStructure #Geology #Science #Nature #postmorerocks
Photo
Add a comment...

Post has attachment
Diabase intrusion in Granite

Here are two igneous rocks, a dark, mafic diabase cutting through a gray-pink granite. This is located near the Silvermine Dam in SE Missouri, among the St. Francois Mountains. The dike, cutting through the granite, is obviously younger; radiometric ages point toward a difference between them of roughly 120 million years.

#Igneous #Geology #PostMoreRocks #Science #Nature #MagmaMonday #MountainMonday
Photo
Add a comment...

Post has attachment
Tension Cracks on a Folded Layer

When rocks are deformed at shallow levels in the Earth's crust, they experience a mix of brittle and ductile processes. As a strong, competent layer is compressed and bends, the outer part of the hinge area can crack. Imagine compressing a long, thin piece of wood from both ends and the board begins to split at the hinge. Here a layer of stone is loaded with tension cracks along the outer arc of the fold. Many of the cracks taper downward to the inner part of the fold and disappear. The outer arc of the layer has to stretch during the folding process, while the inner arc is compressed. This causes stretching on one side and squeezing on the other, and can produce extensional features like these tension cracks. Some of the cracks here appear to be filled with later vein material, precipitated from water. When a layer of rock is buckled in this manner, the strain is concentrated in the hinge, and the rock layer remains largely undeformed in the limbs of the fold. This is the opposite from what happens in some other folding processes, but that's for another time.

#FridayFold #Geology #GeologicStructure #Science #Nature #PostMoreRocks
Photo
Add a comment...

Post has attachment
The 2005 Taum Sauk Reservoir Failure

On Dec. 14, 2005, at ~5 AM, the Upper Taum Sauk Reservoir failed catastrophically, sending 1.3 billion gallons of water down the mountain and through Johnson Shut-Ins in about 12 minutes. The campground was destroyed, but fortunately no one was hurt because it was a week-night in December. The park superintendent’s home was destroyed, but he and his family survived by clinging to trees. The area was stripped down to the bare rock in the area of the scour; many large boulders of granite, rhyolite, and dolomite were deposited in some areas. The park was closed for several years and finally re-opened to full use again in 2009. The Taum Sauk reservoir is a pump-storage hydroelectric plant that pumps water up at night, consuming electricity, and uses the water during the day to generate electricity. The plant was rebuilt and began producing power again in April of 2010. Its two pump-turbine units each are capable of producing 225 MW electrical power.

#energy #geology #science #johnsonshutins #MOStateParks #TaumSaukReservoir
Photo
Add a comment...

Post has attachment
Dikes at Homestake Mine

The yellow rocks cutting through are rhyolite dikes of Tertiary age, intruding through various Precambrian metamorphic rocks that are much, much older. There are many shallow intrusive Tertiary igneous rocks like this in the northern Black Hills, including famous locations such as Bear Butte and Devils Tower. The dikes begin to spread out laterally at the top of the land surface as sills. On the left side of the quarry, not pictured here, this level is roughly even with the boundary with the overlying Cambrian sandstones. So the dikes probably began to spread laterally when they encountered this boundary. The scale in this photo can be a bit difficult to understand at first: there is a road that cuts diagonally that would easily hold large hauling trucks going in and out of the mine. Each cut in the rock between benches would be several tens of feet high. The Homestake mine was the largest and deepest gold mine in N. America until it closed in 2002, and produced more than 40,000,000 troy ounces of gold in the span of its operations. The mine is much, much larger underground than the substantial open pit that is pictured here. It is so deep, in fact that after it closed it was selected as the location for the Deep Underground Science and Engineering Laboratory by the National Science Foundation to conduct scientific investigations of solar neutrinos, tiny sub-atomic particles that can only be studied in extremely careful experiments that block out all other forms of possible interference.

#geology #mining #homestakemine #rhyolite #igneous #neutrinos
Photo
Add a comment...

Post has attachment
Here's a close-up of the Shell Canyon Monocline for today's #FridayFold.

#Geology #GeologicStructure #ShellCanyon #BighornMountains
Photo
Add a comment...

Post has attachment
Bedrock-Constricted River

As the East Fork Black River enters Johnson Shut-Ins, the bedrock changes to a much more resistant layer, and the stream transitions from broad, sandy meanders to a narrow, rough channel in rock. The stream splits into many small segments. Small falls, potholes, and pools dominate. In SE MO, this kind of feature is referred to as a shut-in, where the bed of the river is constricted down to a narrow channel due to a change in the bedrock.

#Geology #Shut-Ins #StatePark #Geomorphology #Rivers #PostMoreRocks #Waterfalls #WaterfallWednesday #longexposure
Photo
Add a comment...

Post has attachment
Cool Contact

When hot magmas intrude into older, cold rocks, they freeze fairly quickly on their margins. As a result, they are finer-grained right next to the contact, and coarser-grained inside this thin rind. Here a pink-white-gray granite (lower left) intruded a greenish gray rhyolite (upper right) and developed this texture quite nicely. The minerals in the granite such as K-feldspar (pink), plagioclase (white), and biotite (black) are all much smaller in size at the contact with the old volcanic rock. This feature is called a chilled margin, and it allows us to determine which rock of the two is the youngest, and which is the oldest. In this case, the granite is younger and the rhyolite is older. By using clues such as these, geologists put rocks in a sequence and determine their relative histories.

#MagmaMonday #Igneous #StFrancoisMountains #granite #rhyolite #geologyrocks
Photo
Add a comment...

Post has attachment
#FridayFold - Small, inclined open folds in silver-gray phyllite from near Devil's Lake State Park, WI.

#GeologicStructure #Science #Nature #Phyllite #DevilsLake #Baraboo
Photo
Add a comment...

Post has attachment
Fossil Meteorite with Cephalopod at the Field Museum

Meteorites that are found have generally fallen out of the sky in the not to distant past. That doesn't mean that they haven't fallen throughout Earth's history, of course, and old meteorite impact sites are well known in the rock record. But the meteorites themselves that fell millions of years ago are pretty rare, because they weather away fairly easily at Earth's surface. A few, however, have been preserved in the ancient rock record as "fossil" meteorites. This one on display at the Field Museum is preserved in a Devonian limestone. The weathering rind is pretty thick, even being encased in the limestone. Some minerals in meteorites, like the spinels, are much less susceptible to weathering and last longer than the olivine, iron, and pyroxenes that dominate chondrites. This one is also special in that it also preserves a beautiful, large cephalopod.

#Geology #Paleontology #Meteorites #FieldMuseum #Science #Nature
Photo
Add a comment...
Wait while more posts are being loaded