Encyclopaedia

  When a thick lava flow  cools it contracts vertically but cracks perpendicular to its directional flow  with remarkable geometric regularity - in most cases forming a regular grid of  remarkable hexagonal extrusions that almost appear to be made by man. One of the  most famous such examples is the Giant’s Causeway on the coast of   Ireland (shown above) though  the largest and most widely recognized would be Devil’s Tower in Wyoming . Basalt also  forms different but equally fascinating ways when eruptions are exposed to air  or water.

  The mysterious moving  stones of the packed-mud desert of Death  Valley have been a center of scientific controversy  for decades. Rocks weighing up to hundreds of pounds have been known to move up  to hundreds of yards at a time. Some scientists have proposed that a combination  of strong winds and surface ice account for these movements. However, this  theory does not explain evidence of different rocks starting side by side and  moving at different rates and in disparate directions. Moreover, the physics  calculations do not fully support this theory as wind speeds of hundreds of  miles per hour would be needed to move some of the stones.  

  A circum-horizontal fire rainbow arc occurs at a rare  confluence of right time and right place for the sun and certain clouds.  Crystals within  the clouds refract light into the various visible waves of the spectrum but only  if they are arrayed correctly relative to the ground below. Due to the rarity  with which all of these events happen in conjunction with one another, there are  relatively few remarkable photos of this phenomena.

  True to their ominous  appearance, mammatus clouds are often harbingers of a coming storm or other  extreme weather system. Typically composed primarily of ice, they can extend for  hundreds of miles in each direction and individual formations can remain visibly  static for ten to fifteen minutes at a time. While they may appear foreboding  they are merely the messengers - appearing around, before or even after severe  weather.  

  While many see these  apparently perfect ice circles as worthy of conspiracy theorizing, scientists  generally accept that they are formed by eddies in the water that spin a sizable  piece of ice in a circular motion. As a result of this rotation, other pieces of  ice and flotsam wear relatively evenly at the edges of the ice until it slowly  forms into an essentially ideal circle. Ice circles have been seen with  diameters of over 500 feet and can also at times be found in clusters and groups  at different sizes as shown above.

Red tides are also known as  algal blooms - sudden influxes of massive amounts of colored single-cell algae  that can convert entire areas of an ocean or beach into a blood red color. While  some of these can be relatively harmless, others can be harbingers of deadly  toxins that cause the deaths of fish, birds and marine mammals. In some cases,  even humans have been harmed by red tides though no human exposure are known to  have been fatal. While they can be fatal, the constituent phytoplankton in ride  tides are not harmful in small numbers.

  Blue holes are giant and  sudden drops in underwater elevation that get their name from the dark and  foreboding blue tone they exhibit when viewed from above in relationship to  surrounding waters. They can be hundreds of feet deep and while divers are able  to explore some of them they are largely devoid of oxygen that would support sea  life due to poor water circulation - leaving them eerily empty. Some blue holes,  however, contain ancient fossil remains that have been discovered, preserved in  their depths.