Gangdong Hwaam Columnar Joint
A compact coastal outcrop in northern Ulsan where roughly 20-million-year-old basaltic-andesite columns lie horizontal, vertical and inclined across the shore
Coastal geology, columnar joints, Miocene volcanism, polygonal rock structures, short geological stops and combining the site with Ulsan’s Gangdong coast
A compact open shoreline with exposed columnar-jointed rock, pebble coast and close views of columns running in several orientations rather than one continuous cliff face
Hwaam is small, but its geology is unusually easy to compare at close range: the columns change direction, and broken faces expose the polygonal pattern that gives columnar joints their name
Character
Gangdong Hwaam spreads columnar joints across a low coastal outcrop. Formed about 20 million years ago, the rock appears in horizontal, vertical and inclined columns, with pentagonal and hexagonal cross-sections visible where individual joints break open
The columns average roughly 20 metres in length and around 50 centimetres across. Their orientation changes over a short stretch of shore, so the same cooling structure can be read from the side as long parallel rock bodies and from the end as polygonal faces
The rock is basaltic andesite rather than simple basalt, with comparatively large plagioclase crystals distributed through it
The experience
The geosite is compact. The main formations sit directly beside the sea, with the strongest views from the shore and the edge of the exposed rock
The changing orientation is the useful thing to watch for. Some columns run almost sideways, others stand more upright, and inclined sections interrupt both patterns. On broken surfaces, five- and six-sided outlines make the cooling geometry much easier to recognize than it can be on a distant cliff
The site remains part of an open coast. Pebbles, exposed rock and the waterline sit close together, and conditions near the formations change with waves and wet weather
History
The rock formed during Miocene volcanic activity roughly 20 million years ago. As lava cooled and contracted, fractures developed perpendicular to the cooling surface, dividing the solidifying rock into long polygonal columns
Later erosion exposed those joints along the present Gangdong coast. Because cooling surfaces and lava geometry differed across the outcrop, the columns now appear in several orientations instead of forming one uniform vertical wall
Hwaam differs from columnar-joint sites at Guryongpo in Pohang and Yangnam in Gyeongju. Its rock is sub-alkaline basaltic andesite, with predominantly pentagonal-to-hexagonal joint cross-sections and plagioclase crystals several millimetres to about one centimetre across
Ulsan designated the site Metropolitan City Monument No. 42 on April 24, 2003. It is the oldest known lava columnar-joint formation on Korea’s East Coast
Before you go
The formations occupy a short exposed coastal section. Public parking and toilets are nearby, and the closest bus stop is only a short walk away. Wet rock and wave conditions can change how comfortably the shoreline itself can be approached
- Hours
- The outdoor geosite is accessible year-round; no fixed daily gate hours are listed
- Access
- Public parking and toilets are available near the coastal outcrop
- Transit
- Hwaam bus stop is a short walk from the geosite and is served by Ulsan buses 722 and 742