Most hexagonal volcanic rock columns in other regions of the world are usually basic basaltic lava. By contrast, the hexagonal columns in Sai Kung are acidic silica-rich rhyolitic volcanic rock. This
extraordinary composition makes them particularly interesting. Their large coverage of over 100 km2 (including sea area) and average diameter of 1.2 m also made them outrival similar columns
in the world. More amazingly, the volcanic rock here has both the features of tuff and lava, and how they have come about has been a topic of debate among geologists to the present day.
High Island
Well arranged hexagonal volcanic columns are well exposed along the coast of High Island. The magnificent hexagonal volcanic column wall at the High Island Reservoir East Dam is like a “Natural Hexagonal Column Mural”, where geographical phenomena like faults, folds, twisted rock columns and dyke intrusions are best appreciated at close quarters. The Tai Long Wan coast nearby showcases a breathtaking coastal landform of volcanic rocks, and justifiably rated
as No. 1 of “Top Ten Hong Kong Natural Attractions” many times.
Ung Kong Group
Together known as the Ung Kong Group, Wang Chau, Basalt Island and Bluff Island consist of hexagonal columns, which are well exposed along the coast. The southeast-facing coastlines, attacked by the relentless waves and wind, showcase some spectacular columnar joints and precipitous cliffs. The 30m-high long sea arch at Wang Chau, the 45m-high sea arch at Basalt Island and the Tiu Chung Arch at Jin Island have entered the list of top four sea arches
in Hong Kong.
Ninepin Group
The Ninepin Group is made up of three larger islands, namely East Ninepin Island, South Ninepin Island and North Ninepin Island, and several small rock islets. Imposing hexagonal columns of North Ninepin Island are particularly breathtaking. Long-term wind and wave erosion of rocks with joints has resulted in many peculiar abrasion landforms. The hexagonal
rock columns here are measured over 2 m in diameter, ranking first in the region.
Sharp Island
Located on the western edge of the Sai Kung caldera, Sharp Island is covered by various volcanic rocks formed earlier than the hexagonal columns, including lava and eutaxite.
In the west it is connected to a small island Kiu Tau by a tombolo made up of cobbles.
For detail information, please visit http://www.geopark.gov.hk/en_landforms.html
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