Situated in northeastern Vietnam, Halong Bay covers an area of approximately 1,553 square kilometers, with nearly 2,000 islands and islets scattered across the bay. Located on the edge of the Gulf of Tonkin, Halong Bay’s geography is defined by its complex system of limestone karsts, sea arches, and lagoons, making it one of the most breathtaking seascapes in the world. 

• Lagoons: Many islands feature enclosed lagoons accessible through narrow sea passages or limestone tunnels. These secluded areas, surrounded by towering cliffs, offer a serene and mystical experience, perfect for exploration by boat or kayak. 

• Marine Lakes of Karsts: Ha Long Bay’s marine lakes are enclosed bodies of seawater nestled within limestone formations, supporting unique ecosystems and salt-tolerant plants. These hidden treasures showcase the diverse Halong Bay landscape and offer a peaceful escape into nature. 

• Tùng (Narrow Sea Inlets): Tùng are deep, narrow inlets carved into limestone islands. These sheltered, fjord-like passages wind through karst formations, providing calm waters and microhabitats for crabs, small fish, and mangroves. Ideal for kayaking, the tùng landscape offer a tranquil escape and a chance to see Halong Bay’s hidden side. 

• Caves and Limestone Pillars: The constant erosion by sea and wind has shaped several islands into towering limestone pillars and caves. These formations are some of the most photographed in the bay, adding a dramatic element to the landscape.

The Halong Bay landscape has been shaped by geological processes over millions of years, with each era contributing to the stunning topography we see today. 

Paleozoic Era – Marine Sedimentation (500 – 250 Million Years Ago) 

During this period, the area was submerged under a shallow sea. Sediments gradually formed thick layers of limestone, which became the foundation for the Halong Bay geography that developed later. 

Mesozoic Era – Tectonic Uplift (250 – 66 Million Years Ago) 

Tectonic movements lifted these limestone beds above sea level, creating the mountainous landscape. Warm and humid conditions during this era intensified the erosion of limestone, setting the stage for karst formation. 

Cenozoic Era – Erosion and Karst Formation (66 – 2.5 Million Years Ago) 

Acidic rainwater further eroded the limestone, carving caves, sinkholes, and underground rivers. Sea-level changes, caused by glacial cycles, helped shape the current Halong Bay landscape, with iconic features such as the Sung Sot and Thien Cung caves. 

Quaternary Period – Rising Sea Levels and Final Shaping (2.5 Million Years Ago – Present) 

The Quaternary period saw the landscape take its final shape, with sea levels rising and carving out the current layout of islands and islets. During the Ice Age, lower sea levels exposed limestone for further erosion, while rising sea levels from melting glaciers isolated limestone peaks as islands. Today, Halong Bay’s karst islands tower above emerald-green waters, enhanced by sunlight reflecting off the shallow seafloor. 

Present Day – Erosion and Preservation 

While major phases of Halong Bay’s evolution are complete, ongoing erosion by rain, wind, and seawater still affects the islands and cliffs. Rainwater continues to dissolve limestone surfaces, contributing to the growth of stalactites and stalagmites in caves. Conservation measures aim to protect this fragile ecosystem from human activity, tourism, and climate change to preserve the bay’s natural beauty for future generations. 

Emerald Green Color: The bay’s waters have a vibrant emerald hue, resulting from factors like mineral content, algae presence, and the shallow depth (averaging around 10 meters), which enhances the color as sunlight reflects off the seafloor. 

Calm Waters: The bay’s sheltered position, surrounded by limestone islands, protects it from strong waves, creating gentle waters ideal for activities like kayaking, swimming, and cruising. 

Tidal Fluctuations: The bay experiences tidal fluctuations of 3 to 4 meters, supporting a diverse ecosystem that includes over 200 species of fish and 450 species of mollusks, further highlighting the richness of Halong Bay geography. 

Ideal for Exploration: The combination of calm, shallow waters and stunning color makes Halong Bay a serene and inviting location for travelers seeking both relaxation and adventure amidst breathtaking scenery. 

The mesmerizing landscapes of Halong Bay are a testament to the power of natural forces that have shaped this area over millions of years. Its towering limestone karsts, tranquil emerald waters, and intricate cave systems make it a geological marvel and a captivating destination for travelers worldwide.

Beyond its beauty, Halong Bay is a living record of the earth’s geological evolution, offering a unique glimpse into the past. From its geological evolution to the gentle emerald waters, Halong Bay is a natural treasure that showcases the grandeur of Vietnam’s landscape. 

So, next time you visit, take a moment to appreciate not just the view but the incredible history and natural processes that have crafted this wonder of the world.