Precariously balanced rocks such as spires, hoodoos, and stacked rocks make interesting scenery.  They also may provide a valuable tool for assessing the seismic stability of an area according to a study by geologists from Arizona State University. (Report referenced below.) They studied balanced rocks in the Granite Dells near Prescott and devised a method of calculating how much ground shaking it would take to destabilize the rocks.   In this post, we will take a look at several types of precariously balanced rocks and see how they form.

The photo above was taken at the Texas Canyon rest stop on I-10 between Benson and Willcox, Arizona.  It shows the weathering pattern and pedestal rocks in the Texas Canyon quartz monzonite (a granite-like rock).  The development of this geomorphology begins underground with chemical and physical weathering along joints in the rock and removal of material to make the joints wider.  Erosion eventually exhumes the rocks.  The photo below from the Chiricahua Mountains shows the results of this process  in somewhat softer volcanic rocks.

Hoodoos, such as these in the Chiricahua Mountains contain a hard capstone over softer material.  The capstone prevents complete erosion of the underlying material.

Perhaps the most spectacular rock spires in Arizona are those in Monument Valley, seen in the photo below on a misty day.  Here, hard sandstone occurs between softer siltstone and shale layers.  The spires are remnants of differential erosion by wind and water.

The Arizona State University study goes into great detail on methodology and technology about proposed analysis of precarious rocks for usefulness is accessing the seismic stability of a region.  One wonders, however, if these rock formations are really as precarious as they appear because the hoodoos and balanced rocks in Texas Canyon and in the Chiricahua Mountains survived the 1887 Sonoran earthquake.

According to the Arizona Geological Survey (Fieldnotes, summer 1987): “On May 3, 1887 Arizona and the Southwest experienced a major earthquake that had an estimated magnitude of 7.2 on the Richter scale.  The epicenter was in Sonora, Mexico approximately 40 miles south of Douglas, Arizona.  The earthquake caused several dozen deaths, damaged buildings as far away as Phoenix, generated rock falls and fires triggered by rock falls in the mountains, and caused panic among the population.”

Reference:

Haddad, D.E., and Arrowsmith, J.R., 2011, Geologic and geomorphic characterization of precariously balanced rocks, Arizona Geological Survey Contributed Report CR-11-B.

See also:

Earthquake hazard near Flagstaff assessed, Video

Where the Next Big American Earthquake and Tsunami Might Occur

Spanish Scientists Find Technique to Predict Earthquakes Claiming 80% Accuracy

The Measure of an Earthquake

Local atmospheric changes may foretell large earthquakes

A recent post from Physicians for Social Responsibility, a historical and sometimes hysterical anti-nuclear activist group, alleges that tritium leaking from nuclear reactors poses a “Threat to Drinking Water” and we should, therefore, get rid of those nasty nukes and replace them with wind turbines and solar panels.

So let’s see if the boogeyman is as dangerous as alleged.  First some background.  Tritium is a form of hydrogen.  Normal hydrogen consists of a proton and an electron.  Tritium has two neutrons in addition.  Tritium can replace one of the hydrogen atoms in water (H₂O) to produce tritiated water (HTO).  Tritium is unstable and decays with release of a very weak beta particle and has half-life of 12.3 years.  Beta particles are rapidly neutralized in the air and cannot penetrate your skin.  However, they can cause soft tissue damage if inhaled or ingested.

Tritium is produced naturally in the upper atmosphere as a result of bombardment by cosmic rays and falls to earth in rain and enters the natural hydrological cycle.  It is also produced as a byproduct of nuclear power generation and some has leaked into the environment.  We all ingest small amounts of tritium when we drink water.  It is rapidly distributed throughout the body in about two hours (hence is not concentrated) and is eliminated in about nine days according the Idaho State University Radiation Information Network.  The Idaho folks say “While not impossible, a large enough dose to cause any significant harm to a person is unlikely.”

The Argonne National Laboratory estimates the lifetime cancer mortality risk from tritium is about 4 in 100 trillion (Link).

The U.S. Nuclear Regulatory Commission keeps track of tritium releases from nuclear reactors.  They say, “these releases either do not leave the power plant property or involve such low levels of tritium that they do not pose a threat to public health and safety.” (Link)

The NRC says also:

•The tritium dose from nuclear power plants is much lower than the exposures attributable to natural background radiation and medical administrations.

•Humans receive approximately 50% of their annual radiation dose from natural background radiation, 48% from medical procedures (e.g., x-rays), and 2% from consumer products. Doses from tritium and nuclear power plant effluents are a negligible contribution to the background radiation to which people are normally exposed, and they account for less than 0.1% of the total background dose.  As an example, assume that a residential drinking water well sample contains tritium at the level of 1,600 picocuries per liter (a comparable tritium level was identified in a drinking water well near the Braidwood Station nuclear facility). The radiation dose from drinking water at this level for a full year (using EPA assumptions) is 0.3 millirem (mrem), which is at least two thousand to five thousand times lower than the dose from a medical procedure involving a full-body computed tomography (CT) scan (e.g., 500 to 1,500 mrem from a CT scan); one thousand times lower than the approximate 300 mrem dose from natural background radiation; fifty times lower than the dose from natural radioactivity (potassium) in your body (e.g., 15 mrem from potassium); and twelve times lower than the dose from a round-trip cross-country airplane flight (e.g., 4 mrem from Washington, DC to Los Angeles and back)”

If Physicians for Social Responsibility were really socially responsible, they would not trot out these fake scares in pursuance of a political goal.  But perhaps Mencken was right when he wrote, “The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary.”

This 215 minute long DVD presents four episodes from the Discovery Channel.

Episode 1: Amazing Earth

This episode, narrated by Patrick Stewart, is a good introduction to earth history.  It discusses plate tectonics, earthquakes, and the history of life.  It has great cinematography and interesting animations.  It suffers from a somewhat melodramatic narration script.  The background music makes parts of the narration hard to hear.  The episode features great photos of erupting volcanos and buildings shaking during an earthquake.

Episode 2: What Lies Below

This episode follows three female scientists as they explore caves in Iceland.  Once again the cinematography is great.  They explore lava tubes and ice caves and have quite an adventure getting to the last cave.

Episode 3: Wild Weather Ahead

This episode is speculative fiction which dramatizes climate scenarios produced by the Earth Simulator, a super computer in Yokohama, Japan. Al Gore would like this episode. The scenarios are interspersed with scenes from the aftermath of hurricane Katrina to add to the drama. This episode qualifies as a B-grade science fiction movie. It demonstrates that even with super computers its junk in, junk out.

Episode 4: Earth, the Sequel

This episode is essentially an infomercial for the alternative energy industry.  The narrator says in the video that government action is necessary to accelerate development of alternative energy schemes (probably because they could not compete in the free market), and that a cap & trade system for the fossil fuel industry is necessary.  Although this DVD has a 2012 date, this infomercial is made partially obsolete by events such as the failure of Solyndra and other solar companies.   The rosy picture painted in the story has been tarnished by reality.

My overall opinion is that the first two episodes are worth watching; the second two episodes are propaganda and not worth your time.  You have to decide if the DVD is worth your money.

The DVD is available from the Discovery Store here for $14.98 or on Amazon here for $13.49.