Jeju-The volcanic island

I'm from South Korea so I will introduce our largest island Jeju. People who live in Korea, they would go to Jeju island because this place is so famous to Korean people. The second picture is a whole part of Jeju island. Jeju island is consist of a lot of basalts. The first picture is called columnar joint that we don't learn yet. This geographical feature is generated by the process that the thick larva is cooled at very fast speed. So if you go to Jeju island, you can see the basalt everywhere.