quake in one's boots
to be afraid, to shake from fear
I was quaking in my boots when my boss told me to come to his office.
Natural Wonders of the World
Jejudo is a volcanic island, 130 km from the southern coast of Korea. The largest island and smallest province in Korea, the island has a surface area of 1,846 sqkm. The island contains the natural World Heritage Site Jeju Volcanic Island and Lava Tubes. A central feature of Jeju is Hallasan, the tallest mountain in South Korea and a dormant volcano, which rises 1,950 m above sea level.