Geohistory - Rocks from Volcanic Islands Period
Scoria is a porous rock formed when splashes of lava with a high amount of gas pile up. As it comes in contact with the air, the iron particles it contains react with oxygen at a high temperature, resulting in the red color of the rock. When scoria piles up around a volcano crater, it is called a scoria cone.
Striped patterns were created by recurring volcanic eruptions. Lava that flowed slowly rather than erupting violently did not oxidize to any significant degree. That is why it is black, despite having the same chemical makeup of red scoria. You can see this phenomenon best at Sekiheki (Red Cliff) on Chiburijima Island and Akiya Coast on Nakanoshima Island.
