tonnes of tangerines harvested in Jeju were flown to North Korea as a sign of appreciation for nearly 2 tonnes of North Korean mushrooms Kim gave to South Korea as a gift, following the September 2018 inter-Korean summit. Archaeology In November 2020, South Korean archeologists announced the discovery of a 900-year-old lost slipway off the coast of Sinchangli. Researchers also discovered bright objects, coins and ceramics belonging to the Northern Song Dynasty. Geography Jeju is a volcanic island, dominated by Hallasan: a volcano high and the highest mountain in South Korea. The island measures approximately across, east to west, and from north to south. The island formed by volcanic eruptions approximately two million years ago, during the Pleistocene epoch. The island consists chiefly of basalt and lava. An area covering about 12% () of Jejudo is known as Gotjawal Forest. This area remained uncultivated until the 21st century, as its base of 'a'a lava made it difficult to develop for agriculture. Because this forest remained pristine for so long, it has a unique ecology. The forest is the main source of groundwater and thus the main water source for the half million people of the island, because rainwater penetrates directly into the aquifer through the cracks of the 'a'a lava under the forest. Gotjawal forest is considered an internationally important wetland under the Ramsar Convention by some researchers because it is the habitat of unique species of plants and is the main source of water for the residents, although to date it has not been declared a Ramsar site. Formation About 2 million years ago, the island of Jeju was formed through volcanic activity. About 1.2 million years ago, a magma chamber formed under the sea floor and began to erupt. About 700 thousand years ago, the island had been formed through volcanic activity. Volcanic activity then stopped for approximately 100 thousand years. About 300 thousand years ago, volcanic activity restarted along the coastline. About 100 thousand years ago, volcanic activity formed Halla Mountain. About 25 thousand years ago, lateral eruptions around Halla Mountain left multiple oreum (smaller 'parasitic' cones on the flanks of the primary cone). Volcanic activity stopped and prolonged weathering and erosion helped shape the island. Climate Jeju has a humid subtropical climate (Cfa in the Köppen climate classification). Four distinct seasons are experienced on Jeju; winters are cool with moderate rainfall, while summers are hot and