Geology of Seoul, Korea

The sediments are typically made up of a variety of materials , including silt , clay , sand , and gravel . It is also composed of mineral grains and rock fragments that originate from the granite and gneiss . This tells us that 1 .8 million years ago (and probably before that , the granite and its surrounding gneiss must have been exposed to erosion at the Earth 's surface Alluvial sediments continue to be deposited today , especially evident in Han River . The river also carries sediment to the Yellow Sea where it is dispersed into deeper water

by ocean currents . Here the sediments are slowly buried , compacted and eventually (over several million years turned into new rock that will preserve fossils of the marine life forms existing during the period of sediment deposition

And so the rock cycle continues . In its simplest form , the sediments become rocks with burial and with deep burial , they are deformed and recrystallized (metamorphosed ) at high pressure and temperature to form gneiss and schist . At some stage , these metamorphic rocks may be heated to a point at which they undergo melting to form granite magma and undergo strengthening or uplifting at a rate of a few millimeters per year . The uplifting causes the growth of mountains that in turn accelerates erosion of all the rock above the granite and gneiss Eventually the granite and gneiss are exposed at the Earth 's surface by this combination of uplifting and erosion where they are once again slowly destroyed by water , ice and wind and carried in bits and pieces back to the sea by rivers . The rocks that underlie Seoul have taken some 2000 million years to undergo the deep burial-deformation-recrystallization /melting-cooling and uplifting part of the rock cycle . They have been on their return journey since at least 2 million years...