High Island's Hexagonal Columns: Hong Kong's Sea-Only Wonder
High Island's Shore of Hundred Thousand Columns: The World-Class Geological Wonder You Can Only See from the Sea
・ Author name: Hansley Tam
・ Publish date: 9/11/2026
The Name Is Not an Exaggeration
“Shore of Hundred Thousand Columns” sounds like marketing hyperbole. It isn't.
Along the coastline of High Island (Leung Shuen Wan) in Sai Kung, you'll find the world's largest group of hexagonal volcanic rock columns—a formation so significant it was selected as one of the First 100 IUGS Geological Heritage Sites in 2022 . These aren't ordinary rocks. They're the cooled, cracked remnants of a supervolcano that erupted roughly 140 million years ago, and they stretch across an estimated 100 square kilometres of land and sea .
You can't hike to most of them. You can't drive there. The best—arguably the only proper—way to see the Shore of Hundred Thousand Columns in its full scale is from the water.
What Makes These Columns So Special
They're Not Basalt. They're Rhyolite.
Most hexagonal rock columns around the world—think the Giant's Causeway in Northern Ireland—are made of basalt, a dark, low-silica volcanic rock. Hong Kong's columns are different. They're rhyolitic, meaning they're rich in silica (around 76%), light in colour, and globally rare .
This isn't a small geological footnote. It's why the High Island Formation stands out internationally. The columns are large—averaging 1.2 metres in diameter, with some reaching 3 metres—and exposed sections can rise up to 100 metres high .
The Scale Is Hard to Process
The High Island Formation isn't a single cliff. It's a sprawling network of columns distributed across Sai Kung's coastline and islands, covering roughly 100 square kilometres . When you cruise past the Shore of Hundred Thousand Columns, you're not looking at one formation. You're looking at the edge of a volcanic system that once reshaped this entire region.
It Survived a Supervolcano
Geologists believe a massive volcanic eruption around 140 million years ago ejected ash and lava across the region. The volcano eventually collapsed, forming a caldera about 20 kilometres in diameter. The volcanic material inside cooled slowly and contracted, cracking into the hexagonal columns you see today . The Shore of Hundred Thousand Columns is one of the most accessible places to witness that ancient process up close—from a safe distance on the water.
How to See It (And Why a Boat Is Best)
By Boat: The Full Picture
The Shore of Hundred Thousand Columns is a signature stop on Splitdyboat's Geopark tours. On the speedboat edition, you cruise directly past the shoreline, getting a panoramic view of the columnar cliffs that you simply cannot replicate from land . The boat slows down, the guide explains what you're looking at, and you have time to photograph the sheer scale of the formation before moving on to the next stop.
Because the columns extend along the coast and into the sea, a boat tour lets you see sections that are otherwise inaccessible. No hiking required, no scrambling over rocks. Just you, the water, and 140 million years of geology.
By Land: A Partial View
If you're determined to see the columns on foot, the High Island Geo Trail along the East Dam of High Island Reservoir offers close-up views of the rhyolitic columns . But that's a different experience—more focused, less panoramic, and it doesn't cover the Shore of Hundred Thousand Columns in the same way a boat tour does. The East Dam is worth a visit, but it's not a substitute for seeing the formation from the sea.
Practical Details for the Splitdyboat Tour
Tour: Geopark Four Sea Arches Volcano Sightseeing Tour (Speedboat or Yacht Edition)
Stop: Shore of Hundred Thousand Columns, High Island
Departure: Sai Kung Pier
Duration: 2 hours (speedboat) or 4–7 hours (yacht)
Price: From HKD $480 per person (speedboat edition)
Suitable for: All ages on the yacht edition; speedboat edition is not recommended for pregnant women, people with back problems, or those prone to seasickness
What to bring: Hat, sunscreen, camera, water, comfortable clothes
FAQ
Can I visit the Shore of Hundred Thousand Columns without a tour?
You can view a very small part of the High Island Formation from the East Dam area on foot, but the Shore of Hundred Thousand Columns itself is best accessed by boat, joining Splitdyboat Guided Hong Kong UNESCO Global Geopark Tour. There is no Public transport to the area, and the coastal sections are not easily reached by land.
Is Hong Kong really home to the world's largest hexagonal column group?
Yes—by area. The hexagonal rock columns stretching between Sharp Island and High Island are estimated to cover more than 100 square kilometres, making the Sai Kung column group the largest known in the world by scale . For comparison, Northern Ireland's famous Giant's Causeway is a celebrated but far more compact formation.
Are the columns really hexagonal?
Yes. The cooling and contraction process created polygonal—most commonly hexagonal—columns. You'll see the pattern clearly from the boat, especially on the exposed cliff faces.
Is this the same as the Giant's Causeway?
No. The Giant's Causeway is basalt. Hong Kong's columns are rhyolitic, which makes them geologically distinct and internationally significant.
How do Hong Kong's columns compare to the Giant's Causeway?
Two things set Sai Kung apart. First, scale: Sai Kung's columns span roughly 100 km², while the Giant's Causeway is a much smaller coastal site . Second, rock type: almost every famous column formation on Earth—including the Giant's Causeway—is made of dark basalt. Sai Kung's columns are rhyolite, a pale, silica-rich volcanic rock that rarely forms tidy columns at all, let alone on this scale . As one geological guide puts it: "the world has many basalt causeways; it has only one Sai Kung"
How tall are the columns, and how wide?
Individual columns average around 1.2 metres in diameter, with some reaching up to 3 metres. Heights can reach tens of metres, with the tallest coastal cliffs at places like Fa Shan rising to about 100 metres . These dimensions dwarf the roughly 0.5-metre diameter columns at the Giant's Causeway .
Why are they called "acidic" columns, and why does that matter?
Rhyolite is an acidic, high-silica volcanic rock. Silica-rich magma is thick and sticky, so it usually erupts explosively as ash rather than flowing as lava. That makes well-formed rhyolitic columns globally rare—and Sai Kung's are considered the world's only large-scale acidic rhyolitic column formation . The columns formed from welded ash from a supervolcano that erupted around 140 million years ago .
Has the site received international recognition?
Yes. The Sai Kung rhyolitic columnar rock formation was selected as one of the First 100 Geological Heritage Sites by the International Union of Geological Sciences (IUGS)—an inaugural global list of the most scientifically important geological sites on the planet . That places Hong Kong's columns alongside sites like the Giant's Causeway in terms of scientific significance.
Will I get wet on the boat?
The speedboat edition may involve some spray depending on conditions. The yacht edition offers a more stable, enclosed ride with air-conditioned seating.
Final Thoughts: The View You Can't Get Anywhere Else
The Shore of Hundred Thousand Columns isn't a photo stop you tick off and forget. It's a reminder that Hong Kong's landscape was shaped by forces most of us can barely imagine—and that some of the best views in the Geopark are only available from the water.
👉 Book your Splitdyboat UNESCO Global Geopark Tour at splitdyboat.com — daily departures from Sai Kung Pier, with the Shore of Hundred Thousand Columns waiting on the route.
This blog post is sponsored by Splitdyboat
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