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. 
A circumhorizontal 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.
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. 
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.
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.Amazing Natural Phenomena
