Rivers and mountains of Korea

About 70 percent of the Korean Peninsula is mountains, yet its average height is only about 448 metres.

A land of old, worn mountains

The NGII national atlas says mountains cover about 70 percent of the Korean Peninsula. Even so, the average height of the peninsula is only about 448 metres, well below the 910 metre average of East Asia as a whole. The atlas explains why: the peninsula has been weathered and eroded for a very long time. Its high mountains are not spread evenly. They lean toward the north and east, along the Taebaek, Nangnim and Hamgyeong ranges, because the north and east were lifted more than the south and west. Geographers call this tilt east-high, west-low.

Baekdusan, Hallasan and the Baekdudaegan

The highest mountain on the peninsula is Baekdusan at 2,744 metres, with a caldera lake, Cheonji, about 3,550 metres across at its summit. It is the source of both the Amnokgang (Yalu) and the Dumangang (Tumen), the rivers that form the border with China (and, for the Dumangang, with Russia). The highest mountain in South Korea is Hallasan on Jeju, 1,947 metres, a UNESCO World Natural Heritage site with the crater lake Baengnokdam at the top and about 370 small volcanic cones, called oreum, around it. On the mainland, the highest summit in the south is Cheonwangbong, the main peak of Jirisan, at 1,915 metres.

Korea also has an older way of mapping its mountains. In the eighteenth century the scholar Sin Gyeong-jun set out a system in a book called Sangyeongpyo, in which all mountains are linked lines branching from one great spine, the Baekdudaegan, running from Baekdusan to Jirisan. The NGII atlas explains the difference from a modern map of mountain ranges. Ranges are drawn from geology, from how the rock formed. The traditional mountain-line map is drawn from divides, the ridges that separate river basins, so it shows where water and people’s lives were divided. In the language of the first unit, the Baekdudaegan is a map of drainage divides.

Rivers that run west and south

Because the land tilts east-high, west-low, most Korean rivers flow to the Yellow Sea or the South Sea. The NGII atlas describes the difference clearly. Rivers that flow into the East Sea are short and steep. Rivers that flow west and south are longer, gentler and have wider basins, so they carry more water. The model above has the same shape; compare a drop on each side. The longest river on the whole peninsula, with the largest basin, is the Amnokgang, 803.3 kilometres long according to the Encyclopedia of Korean Culture. In South Korea the longest river is the Nakdonggang, 510.3 kilometres, and the one with the largest basin is the Hangang, 494.4 kilometres long, whose basin covers 25,953 square kilometres in the South and 35,770 including the North.

Korean rivers also change a lot through the year. Most of the rain falls in summer, so the gap between the highest and lowest flow is very large. The NGII measures it with a coefficient of river regime, the ratio of the largest flow to the smallest. Among the five major rivers the Seomjingang has the largest, 270, nine times the Nile’s 30, a river famous for its floods. Before its dams were built, the Hangang reached 390. That is why Korea has built dams, reservoirs and weirs to hold water for dry seasons, and levees to protect towns from floods.