Evidence of Catastrophic Geology: Case 7

Rifting of tectonic plates can occur much faster than understood by many laymen.  As reported in the journal Nature in 2006, the crust on the side of the Red Sea rift moved apart by 26 feet over a period of just 3 weeks.

Magma entered the crack forming new crust.  Images from the European Space Agency's Envisat radar satellite were used (before and after) to validate the measurement.

A series of small earthquakes had occurred in east Africa the previous year, separating the rift in Ethiopia along a 37 mile long segment (East African Rift).  The Red Sea Rift can be seen in the illustration below.

(image from Saudi Arabian Geological Society)


Satellite monitoring technology has only been recently available to track movement of land masses, and many more events will be examined with keen interest.

Difference between "fracture" and "fissure"

The terms "fracture" and "fissure" are used in my geotechnical engineering reports for Central Texas geology (i.e. limestone formations typically).  These are two different terms and not synonyms.  Both are "discontinuities" in a rock mass.  Discontinuities can be categorized as:

- Fractures
- Joints
- Bedding planes
- Cleavage or foliation
- Faults

When a crack forms along a rock cleavage plane, some prefer not to associate the term fracture with this type of discontinuity.  But joints are also fractures.

A fracture develops mechanically in rock due to a failure of structure under tensile stress (the initial stage of a crack) or stress-strain conditions due to environmental or man-made conditions.  When shear stresses parallel to the plane of the crack are out of equilibrium, sliding may occur (i.e. fault).

A fissure is a specific shape of fracture, one that is long and narrow.  It is also a discontinuity dividing an otherwise continuous rock material without separation in 2 of 3 dimensions (i.e. no sliding has yet occurred; separation in 1 dimension).  A fissure may be void or may have been filled in.  A fracture or a joint with a visible opening (aperture) and a long or deep alignment can be called a fissure.

Empirical Evidence of Catastrophic Geology: Case 6

Glaciers in the early 21st century have generally been losing mass (melting) and "retreating" due to changes that occur in the climate.  Glaciers can experience cycles of growth and retreat.  The "Fox" glacier in New Zealand for example retreated 985 feet horizontally in 2014.  As glaciers in valleys retreat, the toe of the side slopes loses resistance (buttress) that permits shallow to deep slope instability failures.  The landslides add notable "sediment" to the valley and deposit variable thicknesses of sediment in an instant.  In addition, the glacier water collects more loose sediment from the side slopes from rainfall runoff and shallow slides, causing fast sediment building in the stream valley.  At the "Fox" glacier valley for example, valley sedimentation is occurring at a rate of more than 3 feet per year (another example of a relatively fast rate of buildup for a sedimentary deposit).  A photograph of the "Fox" glacier is provided below.

Empirical Evidence of Catastrophic Geology: Case 5

Contrary to typical layman belief, marine deposits on or near a continental shelf are not commonly formed by slow, gradual, consistent sedimentation from near the surface from soil particles derived from river deltas or continental runoff (terrigenous) or from organic byproducts (i.e. coccolithophorids - planktonic algae - debris that forms part of chalk, i.e. biogenetic ooze).  Much of the sedimentation and the geologic features are created by deposition by massive debris flows, turbidity currents, and slumps (slope failures).  These are in addition to overall "fan" valley and channel complex features from currents originating from the river sources.  A conceptual image of a rapid debris flow and turbidity current (by Mike Clark) is provided below.  Debris flows can be hundreds of meters high and move as rapid as 30 mph.  Turbidity currents, debris flows, and slope failures can also be instigated by earthquakes and volcanic activity.

Erosion features are also commonly formed by high velocity underwater flows and include gulleys on the upper continental slope (tens of meters to hundreds of meters deep!) and canyons several km wide and hundreds of meters deep.  Sub-marine fans can be a few km to several thousand km wide.

Large thicknesses of sedimentation therefore occur in marine environments near continental shelves or submarine volcanoes and mountain ranges within a matter of minutes, hours, and days, and not "millions of years".

Rapid deposition by debris flows, slumps, and sediment dense turbidity flows will cause rapid burial of organisms (plant and animal life) and permit fossilization.

Sub-marine geology and sedimentation is highly complex as discovered by advanced studies performed with every passing year.  More and more literature is available describing these processes and there is still much to be learned because much is still hypothesized (i.e. debate over coarse turbidity deposits).

Empirical Evidence of Catastrophic Geology: Case 4

The Ricobayo dam is a 320-ft tall concrete arch dam constructed in 1929-1933 in northwest Spain.  The original spillway was originally a simple 1300-ft long channel cut in the rock (unlined channel) that discharged over a rock cliff.  Floods (high water levels) occurred in 1934-1936 and scour (loss of rock mass) was observed within the spillway channel and plunge pool.   100 meters of granite rock along the spillway was scoured away during this time (80 ft in 1935 and 100 feet in 1936 to start), creating an entirely new downstream valley profile.

  

(Photo was reproduced from an article by George Annandale, P.E.).  The Ricobayo spillway consisted of granite with vertically dipping joints and 10 to 20 degree off horizontal joints.  The plunge pool of the spillway was relatively stable after a certain depth of scour had occurred (80 feet), due to the presence of harder rock starting at a certain elevation, although the concrete lining was destroyed by forces from a flood in 1939 and again in 1962.  The fractured/jointed condition of the rock permitted water infiltration and a reduction of effective stresses within the joints that facilitated loss of rock mass.  This case history reminds us of the power of water and the ability to alter topography and geologic profile very quickly.  A more recent photo of the dam is provided below.  Note the huge vacant rock space.

Paleontology: Dinosaur Footprints in Leander, Texas

In Leander, Texas, along the stream bed of the South Fork of the San Gabriel River, dinosaur (extinct reptile) footprints are evident in the exposed limestone.  This location is west of the US183 and San Gabriel River intersection right at the first bend in the stream valley.

The geology consists of inter-bedded limestone rock, marly (clayey) limestone, sandy clay-marl, weak limestone material, and nodular limestone sedimentary deposits categorized as the "Walnut Group" geologic formation that includes "Cedar Park Limestone", "Bee Cave Marl", and "Bull Creek Marl" members.  The layers of marl and weak limestone materials are erodible, so the currently exposed dinosaur footprints are in a limestone rock layer (resistant).  The stream valley walls show evidence of inter-bedding as the overlying layers have eroded while the currently exposed rock layers have remained more resistant to stream flood water erosion and weathering.

The photo shows the largest tracks, assumed to be from a theropod or ornithopod type dinosaur.  There are some other smaller tracks scattered around also from 3-toed (tridactal) dinosaurs.  This geologic formation was either deposited during the ascending phase of one creationist geologic model when footprints would have been made in soft (yielding) soil and quickly buried and preserved by the next event of sedimentation, or during the Cretaceous age of the uniformitarian model of millions of years, depending on which paradigm someone is working under. If working under the creationist model this strata was likely buried under subsequent sediment layers but then subsequently exposed after the abative geologic phase eroded off alot of the overlying strata and river floods finished off the rest to expose the site in its current condition.

Chert vs Flint

Chert rock is common in the "Edwards" geologic formation here in central Texas.  A more common layman term is "flint".  Chert is a rock (not a mineral) composed of microscopic quartz crystals (microcrystalline).  Chert has a smooth surface and fractures with a conchoidal shape.  Chert is found as nodules (subrounded mass) or layers of limited horizontal extent within limestone rock.  Chert occurs in many colors such as white, yellow, red, brown, green, blue, gray, and black.  The yellowish, red, and brown chert is commonly called "jasper", while the dark gray to black chert is commonly called "flint".

The conchoidal fracturing is what made "flint" a popular rock type for carving an otherwise very hard material and making arrow heads, spear tips, or knives.  The image at right includes an arrowhead made of chert found in Georgetown.  The other two items are very dark gray to black chert rock fragments (flint).