In the previous post, I discussed the many meanings of the word shock.  In this post, I focus on the specific properties of shock waves as compression waves in air, and the expansion (rarefaction) waves that follow the shocks in order to bring the pressure back to ambient.  THIS IS A DRAFT ONLY, AND WILL BE PROOFED SHORTLY. Shock waves in air can be generated in a number of ways, e.g., by a supersonic aircraft, a speeding bullet, or an erupting volcano.  The general physics of such waves can be envisioned by considering a pipe that has a barrier (referred to as a diaphragm) sepa ..read more

   This is the first of a series of articles on shock waves in physical systems and, over time, it will be updated to cross-reference to a parallel set of articles by a colleague who works with human systems. I will add more posts that discuss shock waves in various other physical systems. Please stay tuned to GeologyInMotion.com in the future! The word "shock" has developed many meanings and uses since it's origin in about the 1560's A.D. At that time, "shock" was a military term meaning a "violent encounter of armed forces or a pair of warriors." It derives from the French word "c ..read more

 https://www.youtube.com/watch?v=LWywL3XWEbA ..read more

  La Soufriere St. Vincent last erupted in 1979 with a volcanic explosivity index (VEI) of 3, causing evacuation of 20,000 people. In 1902-1903 it had a VEI4 eruption that caused ~1500 deaths. Ironically, this eruption was somewhat overshadowed because it was one day before the catastrophic eruption of Mt. Pelee in Martinique, an eruption that destroyed St. Pierre.** There were also eruptions in 1718 and 1812, giving a rough cyclicity of explosive eruptions every 77-94 years. (left figure) Soufriere St. Vincent is shown at the north end of the island in brown shading. It rises to a heig ..read more

 A small volcano, Volcán Bárcena,  480 km off the west coast of Mexico, displays an unusual set of grooves that were carved during an eruption in 1952. The volcano came to life, grew to 335 m elevation, and ended eruptions all in the short span of 7 months.  There were three phases in this eruption: (1) formation of its base by eruptions starting on August 1; (2) creation of a large crater in the summit; and (3) eruption of lava at the base.  The eruption was only intermittently observed and those observations were documented by Adrian Richards, a scientist who was working ..read more

 For any reader who is watching the current impeachment proceedings in the U.S. Senate, I point to an earlier post that I did a year ago during the first impeachment proceedings. It was titled "The most interesting thing about the U.S. Senate impeachment hearings? THE ROCK!! (I should probably have titled it "The most interesting thing to a geologist about the...". See the link below: https://www.blogger.com/blog/post/edit/4706799725776420299/9021789599785857658   The rostrum is a veined marble from Italy or Turkey called Rosso Levanto, meaning "red from the Levant." The figure show ..read more

  Note added February 8, 2021: An example of a rare, high-consequence event occurred today in India: a chunk of a Himalayan glacier broke off and unleashed a flood that took out one dam and seriously affected another, took out two hydroelectric power plants and killed at least 14 with another 170+ missing. This is not only an example of a rare event, but also of a compound event: a piece of glacier fell off, created a wall of water and mud that barrelled down a valley, and destroyed dams and infrastructure. It is also a combined natural disaster and engineering disaster. More info here ..read more

Glacier mice in Iceland. Hotaling et al. In the 1950's an Icelandic researcher, Jon Eythorsson, described the features shown in the photo to the left as "rolling stones [that] CAN gather moss," and dubbed them "glacier mice." These balls of mass are not attached to anything and just rest on the ice...but they move around in a "coordinated herd-like fashion" (Hotaling et al., 2020 as reported here by NPR).    Hotaling et al., describe these as "soft, wet, squishy pillow(s) of moss" that seem to form out of different moss species nucleated around an impurity such as a rock or ..read more

   Cleveland Volcano, Alaska, 2006. NASA image. The COVID-19 pandemic is the focus of attention in many ways during 2020 and is likely to remain so for months, if not years, to come. Because of its long duration other disasters are likely to occur: some could be technological (e.g., electrical grid failures, computer network problems, nuclear reactor difficulties) and some will inevitably involve the natural world of which we humans are a part. These additional disasters are being referred to as "compounding events" by the media and agencies involved in responding to them ..read more

In the U.S. Senate hearings on the impeachment of President Donald Trump, the Chief Justice of the Supreme Court, John Roberts, sat high behind a dark rostrum of veined marble. It appears to be Rosso Levanto, a veined marble from Italy and/or Turkey (the name means "red from the Levant"). It is typically deep purple or cherry red (but appears black in the images I've seen on TV and on the WWW). In 1949-1950, the Senate Chamber was renovated and pilasters of Rosso Levanto replaced cast-iron originals, and the wooden rostrum was replaced with the same marble.      One of the ..read more