Geohistory - Rocks from Volcanic Islands Period
Scoria is a porous rock formed when splatters of lava with a high amount of gas keep piling up. As it came in contact with air, the iron particles it contains reacted with oxygen at high temperature, resulting in the red colour of the rock. Formations made with piled-up scoria by the volcano craters are called scoria cones.
Recurring volcanic eruptions created the striped pattern. Lava that flew slowly rather than being violently ejected, did not oxidate to any significant degree. That is why it is black, despite having the same chemical makeup red scoria. We can see this phenomenon best at the Sekiheki Cliff on Chiburijima Island and Akiya Coast on Nakanoshima Island.