Korea has a diverse and interesting geologic history and owes much of its natural beauty to the rocks underneath the landscape. Bedrock that is resistant to weathering and erosion forms high rugged mountains, while less resistant rocks characterize the lowlands, basins, and valleys. Sites of particular geological significance have been preserved as twenty two National Parks, seven Geoparks, and nine Ecological Landscape Conservation Areas across the country. Although Korea does not currently have active volcanoes, vigorous volcanic activity occurred at various times in the past and so there are volcanic rocks and landforms in various regions. Ulleungdo and Dokdo islands, for example, are the exposed peaks of a submarine volcano. Other regions have a soluble rock, limestone, which can be dissolved to form caves and dolines (sinkholes).

  The geologic map shown in the next page has been simplified to show the locations of the three main rock types: igneous, sedimentary, and metamorphic. Any of these rock types can be transformed to any other type through the rock cycle. More than two thirds of the Korean Peninsula consists of igneous and metamorphic rocks. By studying rocks and their distributions, geologists can work out the ancient history of Korea as it was shaped by volcanism, tectonic plate movements, erosion, and a sedimentation history that goes back billions of years. The oldest rocks in Korea are about 2.5 billion years old.
 

  The geology of the Korean Peninsula is very important for interpreting the tectonic relationship between Korea, China, and Japan. As the East Sea was formed, it separated Japan from Korea and uplifted the eastern part of the Korean Peninsula. Due to the uplift, the eastern part of the Korean Peninsula was elevated higher than the western part, resulting in westward tilting. The Peninsula is relatively safe from earthquakes compared to Japan, which is located on the plate margin, but it is not completely safe. Although not abundant in most cases, many kinds of mineral resources have been found on the Korean Peninsula.

Igneous Rock forms by solidifying directly from a molten state. The most common igneous rock in Korea is granite, which solidifies while the body of molten magma is still underground. Many granite and volcanic rocks in Korea were formed during the Mesozoic period about 250 to 66 million years ago. Most granites are milk-white in color but alkali granites show a pinkish red color.

Sedimentary Rock is formed by the consolidation of sediments that have accumulated in an area. Many sedimentary rocks in Korea were deposited during the Tertiary period (66 to 2.5 million years ago) and the Quaternary period (2.5 million years ago until the present). The main sedimentary rocks are shale, sandstone, conglomerate, and limestone.

 

Metamorphic Rock is formed by applying heat and pressure to a rock to physically or chemically change it. Most metamorphic rock in Korea formed in the Pre-Cambrian period (more than 540 million years ago). In Korea, metamorphic rocks consist of mainly gneiss and include schist, phyllite, quartzite, marble, and amphibolite, which formed by the metamorphism of shale, sandstone, limestone and basic igneous rocks.