Hin Muang

Hin Muang (Purple Rock) — Andaman Sea, Southern Thailand

Hin Muang — 'Purple Rock' — is a submerged seamount in the southern Andaman Sea, 50 km southwest of Koh Lanta, paired with the adjacent Hin Daeng ('Red Rock') two kilometres away. The two sites are always dived together on a day trip or liveaboard stop, and they represent the most dramatic diving in southern Thailand.

Why 'Purple'

The name comes from the purple soft corals (Dendronephthya) that blanket the seamount walls from about 15 meters to beyond recreational depth. At its best — on an incoming current when the polyps are fully extended — the seamount walls look like a vertical garden of purple and white, fluorescent against the blue. Few reef environments in Thailand match the colour density of Hin Muang in peak condition.

The Depth and the Pelagics

Hin Muang is significant partly because it is genuinely deep. The seamount descends below 70 meters on its outer faces, and the shallower zone (20–40 meters) where most recreational diving occurs sits within range of pelagic species that don't appear at shallower Andaman sites.

Manta rays — both reef mantas and oceanic — appear at Hin Muang with reliable frequency from November through May. The mantas here are often feeding rather than cleaning, spiralling through plankton concentrations in the mid-water. Whale sharks pass through from February through April, using the seamount as a navigation marker in open-ocean transit. Grey reef sharks and silvertip sharks patrol the deeper sections.

Conditions

Hin Muang is exposed — there is no shelter from current or swell on the seamount's outer faces. Spring-tide dives here can involve powerful currents, and the 70-meter depth means gas management requires attention for divers who descend below 40 meters. Most operators brief a maximum recreational depth of 40 meters and stick to the well-colonised middle sections of the wall.

Best season: November through May (Andaman open season); closed during monsoon (June–October) as the site is too exposed to dive safely.

Practical Info

• Depth: 15–70m | Difficulty: Advanced — strong current, depth, exposed location
• Access: Day trips from Koh Lanta or Koh Phi Phi (2–3 hrs by speedboat); liveaboard
• Best season: February–April for mantas and whale sharks; November–May overall
• Marine life: Manta rays, whale sharks, silvertip sharks, grey reef sharks, purple soft coral walls