Hang Son Doong

The World's Largest Natural Cave
Son Doong is the largest cave on Earth and also the most magnificent cave in Vietnam. Discovered by a local logger named Ho Khanh in 1990, the cave's entrance was explored by the British-Vietnamese Cave Expedition Team led by Howard Limbert in 2009 for mapping, surveying, and exploration. In 2009, the cave was declared the world's largest natural limestone cave by the expedition and National Geographic. In 2013, Hang Son Doong was officially recognized as the world's largest natural cave by the Guinness World Records.

Origin of the Name Hang Son Doong
According to cave exploration tradition, the discoverer has the privilege of naming the cave. After the expedition concluded in April 2009, Ho Khanh was proposed to name the cave, with suggestions to name it after him. However, Ho Khanh, along with the expedition members, decided to name the cave Hang Son Doong, a combination of two words: Son, meaning mountain, and Doong, the name of the valley where the Rao Thuong River flows, or interpreted as a cave within a mountain (limestone) with an underground river.

Unique Features of Son Doong Cave
Son Doong Cave has a total length of nearly 9km, a vast cave chamber, and a volume of up to 38.5 million cubic meters, making it the largest natural cave on the planet. The volume of Son Doong is over 5 times larger than Malaysia's Deer Cave, previously considered the world's largest natural cave (before Son Doong's discovery) with a volume of 9.5 million cubic meters. What sets Son Doong apart and captures the world's attention is its unique features inside the cave: gigantic stalagmites (over 80m tall), a thriving primary forest within the cave, an ecosystem, its own weather system, and an endless underground river yet to be fully explored by any expedition.

Many visitors describe Son Doong as entering another world, while ABC News' Good Morning America's MC Ginger Zee compared the cave's scenery to the movie Avatar. Below are the highlights and many unique aspects found inside Son Doong Cave.

Discovery Journey and Notable Milestones
The discovery of Son Doong, the world's largest natural cave, began with a local man named Ho Khanh, who grew up in the Phong Nha region in Quang Binh province, Vietnam. In 1990, during a routine trip to the forest to search for agarwood, Ho Khanh stumbled upon a small cave entrance hidden behind a limestone mountain wall. Approaching the cave, he noticed thick mist blowing out from the small entrance, accompanied by the sound of a rushing stream inside. Feeling the cold breeze from the cave, Ho Khanh decided to leave without further investigation, forgetting its exact location upon returning home.

In 2007, Howard and Deb Limbert, leaders of the British Cave Expedition Team, arrived in Phong Nha and began searching and surveying caves in the area. Based on the analysis of the limestone mountain terrain, river systems, and geological formations, Howard Limbert predicted the existence of a large cave beyond the region of Swallow Cave but did not know its exact location. During a conversation with Howard, Ho Khanh casually mentioned the cave he had seen with strong winds, dense fog, and echoing sounds. Howard and Deb were excited and urged Ho Khanh to try to remember the location and guide them to the area with this mysterious cave entrance.

Recognizing Howard Limbert's dedication and efforts, Ho Khanh continued his search for the mysterious cave entrance over the years. In 2008, during another hunting trip, Ho Khanh fortunately rediscovered the location of the seemingly forgotten cave entrance. He carefully noted the cave's location by orienting himself with the surrounding mountains and memorizing the route in his head before returning to find a way to contact the expedition team.

On April 7, 2009, Howard Limbert organized an expedition in collaboration with the Natural Sciences Faculty of Hanoi National University to explore and survey the cave, which was not yet named at the time. The first person to step inside the cave was Peter MacNab, a member of the British-Vietnamese Cave Expedition. This was also Ho Khanh's first time entering the cave due to the lack of safety equipment in previous visits. During this exploration, along with laser measurement results, the expedition team determined that Son Doong was the world's largest natural cave. Ho Khanh and the expedition members then discussed and named the cave Son Doong, combining the words Son (mountain) and Doong (the name of the valley where Rao Thuong River flows through Bản Đoòng, the home of the Bru Vân Kiều people since 1992). With the power of domestic and global media, Vietnam and the cave exploration team officially introduced Son Doong Cave to the world. Subsequent revelations about the world's largest cave, its dimensions, and the unique ecosystem inside left the world in awe.

Timeline of Son Doong Discovery and Surveys
Early December 1990: Ho Khanh, during a forest trip, discovered the cave later known as Son Doong.
April 7, 2009: Ho Khanh led the British-Vietnamese Cave Expedition, led by Howard Limbert, to survey and map the cave. Peter MacNab was the first person to step inside the cave.
April 14, 2009: The cave was named and declared the world's largest natural cave. National Geographic magazine announced it as the world's largest natural cave.
March 17, 2010: The expedition team climbed Vietnam's Great Wall to exit the cave, completing the survey and mapping of the entire 9km length and 38.5 million cubic meters volume of Son Doong. National Geographic TV declared it the world's largest natural cave.
2013: Son Doong Cave was officially recognized by Guinness World Records as the world's largest natural cave.
March 31, 2019: Howard Limbert, along with world-renowned cave divers such as Martin Holroyd, Rick Stanton, Jason Mallinson, Chris Jewell, conducted a cave diving expedition into the underground river inside the world's largest cave. After nearly a week of exploration, the team discovered an underwater passage at a depth of 90m. If this passage connects to Hang Thung, the volume of Son Doong Cave will increase by an additional 1.6 million cubic meters. Further expeditions are planned to explore this underwater section in the future.

Son Doong Cave Surveys
In 2008, after receiving a letter from Ho Khanh about finding a cave with a strange cold breeze and fog blowing from the entrance, which he had mentioned to Howard Limbert in 2005, Howard Limbert recognized that this could be a large cave with a disappearing underground river that he and his colleagues had been searching for since 1994 when surveying Swallow Cave.

April 2009: Howard Limbert, along with team members Helen Brooke, Peter MacNab, Jonathan Sims, Adam Spillane, Trevor Wailes, Deb Limbert, Sweeney, and some lecturers from the Faculty of Natural Sciences at Hanoi National University, conducted a survey of Son Doong Cave. However, the expedition had to stop at a massive rock wall without specialized equipment to overcome it, forcing them to retreat using the original path. Despite the halt, Howard Limbert, along with National Geographic magazine, announced the cave as the world's largest natural cave based on the obtained survey data."

In March 2010, Howard Limbert and the exploration team returned, equipped with specialized gear to overcome the massive barrier. Accompanying them were scientists and a film crew from the National Geographic TV channel to document the exploration of Son Doong Cave and the journey through the large barrier, later known as the Vietnam Wall. After overcoming the Vietnam Wall, the team continued for another 600 meters, reaching the cave entrance, completing the expedition. The exploration team determined the cave's volume to be 38.5 million cubic meters, more than five times larger than the Deer Cave in Gunung Mulu National Park, Sarawak, Malaysia, previously considered the world's largest cave at that time with a volume of 9.5 million cubic meters. The measurements and methods used were acknowledged by renowned geologists, including Dr. Tony Waltham. Son Doong was officially announced by National Geographic TV as the world's largest natural cave in the documentary film "The World's Biggest Cave," released in the same year.

Location and Map of Son Doong Cave
Located in the core area of Phong Nha-Kẻ Bàng National Park, in Tan Trach commune, Bo Trach district, Quang Binh province, Son Doong is a newly discovered cave explored by the British-Vietnamese Cave Exploration Team. To reach the cave, tourists must participate in an adventure tour organized by the Oxalis Adventure company, the only licensed entity permitted to bring tourists to explore Son Doong Cave.

World Records and Media Coverage of Son Doong
Upon completion of the survey, National Geographic Magazine (2009) and National Geographic TV (2010) declared Son Doong Cave the world's largest cave with a volume of 38.5 million cubic meters, surpassing the previous record held by Deer Cave in Malaysia with a volume of 9.5 million cubic meters.

Son Doong was officially recognized by the Guinness World Records as the world's largest natural cave in 2013. In 2015, Guinness reaffirmed its recognition of Son Doong as the world's largest cave by volume (38.5 million cubic meters).

In 2014, The New York Times voted the cave as one of the 52 most attractive tourist destinations in the world.

In 2015, the world's largest cave was featured in a live broadcast on ABC News' Good Morning America, marking the first time a cave of this size was shown live on television.

Also in 2015, National Geographic released a high-quality 360-degree photo series with sound captured inside Son Doong Cave.

In 2019, DJ Alan Walker created a music video titled "Alone P.II" filmed in Son Doong Cave, which gained 275 million views worldwide by October 2022.

In 2020, Business Insider recognized the cave as one of the 20 natural wonders breaking records.

In 2021, National Geographic's Son Doong 360 photo set became a virtual reality tour, gaining global popularity during the pandemic.

On April 14, 2022, in celebration of Son Doong being declared the world's largest cave, Google Doodle honored the cave on the Google search homepage in 18 countries, including Vietnam, Argentina, Chile, Costa Rica, Dominica, El Salvador, Greece, Guatemala, Honduras, Mexico, Moldova, Romania, Singapore, Sweden, Thailand, the Virgin Islands of the United States, the United Kingdom, and Brazil.

On November 26, 2023, Son Doong Cave appeared in episode 6 of Planet Earth III - Extreme, a renowned nature documentary by BBC.

Tourism Operations
Before 2011, cave tourism activities in Phong Nha-Kẻ Bàng mostly focused on general tourist caves such as Phong Nha Cave, Paradise Cave, Thien Duong Cave, alongside ecotourism areas like Mooc Stream and Dark Cave. These activities attracted around 500 thousand visitors annually, but most tourists returned to stay in major cities like Hue, Da Nang, and Dong Hoi after cave tours. Local residents had limited opportunities to participate in tourism activities, leading to ongoing difficulties in their lives, prompting some to engage in illegal logging and hunting.

In 2013, the provincial People's Committee of Quang Binh allowed Oxalis Adventure to operate adventure tourism with a 6-day and 5-night itinerary for Son Doong Cave. Test tours were conducted in August 2013, and by 2014, the official Son Doong Expedition tours were launched.

With a core value of ensuring safety for tourists and team members, preserving the cave landscape, and community involvement, Oxalis has been working to bring positive changes to Phong Nha - Quang Binh and Vietnam as a whole through Son Doong.

Son Doong's Tourism Impact
Son Doong has played a significant role in promoting the development of cave tourism in Quang Binh, putting the province on the global tourism map. It has provided employment opportunities and improved the lives of local residents. Due to the tourism boom, various tourism services have emerged, with hundreds of families establishing homestays to accommodate tourists. The Son Doong Expedition tours directly created jobs for 125 local residents in Phong Nha and indirectly generated employment for many more through additional services, food supply, and various other services. Tourism activities at Son Doong have contributed to the local economic development of Quang Binh.

Emmy Award-winning filmmaker Sid Perou visited Son Doong and Phong Nha, creating a 40-minute documentary titled "Son Doong, the Cave That Lifted a Village." The film gained international acclaim and attracted many tourists to Phong Nha, Quang Binh. Today, Phong Nha-Kẻ Bàng is a captivating destination for both domestic and international tourists, and the lives of local residents have gradually improved.

Geology, Topography, and Ecosystem of Son Doong Cave
Geology and Topography
Son Doong Cave is situated in the limestone mountain range, the largest in Southeast Asia, formed over 400 million years ago. The limestone blocks were created through both chemical and biological processes. Chemical limestone formed as a result of the precipitation of CaCO3 from the solution of Ca(HCO3)2 in seawater. Biological limestone, also known as biogenic limestone, primarily formed from the skeletons and shells of organisms containing CaCO3. Shells of clams, snails, corals, and most types of coral skeletons could be the initial materials for biogenic limestone. After the Earth's crust movements, accumulated layers rose to form limestone mountains as seen today.

Son Doong, considered the world's largest cave, is estimated to have formed around 2-3 million years ago. It developed on a fractured section of the Truong Son mountain range, eroded by the Rao Thuong River over millions of years. The river, containing carbonic acid, infiltrated or flowed through the limestone, causing the dissolution of calcium in the limestone, forming a massive underground passage beneath the limestone mountain. Large collapses in the ceiling occurred where cracks were extensive, creating magnificent sinkholes in Son Doong as we see them today. The ongoing processes of movement and cave formation in Son Doong continue.

"Ecosystem Inside Son Doong Cave

Son Doong is currently the largest cave in the world, with a length of 9km. Inside Son Doong Cave, there is a cavern with a height of over 200m and a width of more than 150m. Some sections of the cavern have collapsed, forming sinkholes (skylights) that allow light to penetrate inside the cave, creating conditions for plants and various vegetation to thrive. Scientists have discovered over 200 plant species inside the world's largest cave, including moss, algae, some climbing plants on rock walls, shrubs, small trees, and large trees exceeding 30m in height. Inside the cave, there is an underground river with large flows, areas with deep water pools, and habitats for various fish species that have adapted to the perpetual darkness inside the cave.

As of now, researchers have identified more than 7 new species inside Son Doong Cave, including some fish species, cave crickets, millipedes, spiders, and beetles, all characterized by the absence of eyes and transparent bodies.

Son Doong Cave has a massive volume, capable of accommodating skyscraper-sized structures, with sections wide enough for a Boeing airplane to fly through. Inside the cave, there are streams, waterfalls, and even primeval forests. With such immense size, the world's largest cave has its own weather system, with temperatures inside ranging from 22 to 25 degrees Celsius in the summer and 18 to 22 degrees Celsius in the winter. During the summer, the cave's interior temperature is generally lower than the outside temperature, ranging from 8 to 12 degrees Celsius, due to the influence of the underground waterfalls and the air pressure difference between the inside and outside of the cave, creating clouds (mist) inside the cave.

Nature has created a unique and fascinating ecosystem inside Son Doong Cave that cannot be found anywhere else.

Unexplored Mysteries of Son Doong Cave

Despite the 2010 Vietnam Wall expedition helping explorers find an exit and complete the mapping of Son Doong Cave, there are still many unexplored mysteries. During expeditions from 2010 to 2022, Howard Limbert's cave exploration team discovered and surveyed many caves around the Son Doong area. Notably, during the mapping of Hang Va in 2012 (discovered by Ho Khanh in 1994) and integrating it into the current cave system map, the exploration team found that Hang Va is located right below the entrance to Son Doong, about 50m from the Vietnam Wall.

During surveys, the exploration team discovered an underground river inside the world's largest cave suddenly disappearing at a water pool called Doline 1, about 4.5km from the cave entrance. Cave experts suspect that this underground river may connect to Thoong Cave (Hang Thung) about 600m away. In 2019, Howard Limbert, along with experts Martine Holroyd, Chris Jewell, Rick Stanton, and Jason Mallinson, who participated in the cave rescue team in Tham Luong Cave in Chiang Rai, Thailand, conducted a dive. They discovered an underground river at a depth of 60m, but due to inadequate diving equipment at that time, the team decided to use a survey to announce the discovery of the underground river at a depth of 60m. If the survey is successful and connects Son Doong to Hang Thung, the volume of Son Doong could increase by 1.6 million cubic meters. The world's largest cave still holds many mysteries waiting for explorers to uncover. In March 2023, Howard Limbert's cave diving team, including cave diving experts John Volanthen and Martin Holroyd, will continue to dive and survey from Hang Thung to search for a connection to Son Doong.

Phong Nha - Ke Bang National Park, a World Natural Heritage Site

Phong Nha - Ke Bang National Park
Son Doong Cave is located in the core area of Phong Nha-Ke Bang National Park, a UNESCO-recognized World Natural Heritage Site in 2003 and 2015.

Phong Nha - Ke Bang National Park was established in 2001, inheriting from the Xuân Sơn special-use forest (1986) and the Phong Nha nature reserve (1993). Phong Nha - Ke Bang National Park covers an area of ​​123,326 hectares, including 03 zones: strictly protected zone (100,296 hectares), ecological restoration zone (19,619 hectares), and administrative-service zone (3,411 hectares).

In 2003, Phong Nha - Ke Bang National Park was first recognized by UNESCO as a World Natural Heritage Site for its outstanding global geological, geomorphological, and geographical values. In 2009, it was recognized by the Vietnamese government as a special national monument. In 2015, Phong Nha - Ke Bang National Park was recognized by UNESCO for the second time as a World Heritage Site with new criteria for outstanding global biological diversity.

Phong Nha - Ke Bang has the largest limestone mountain range in Southeast Asia, with a dense system of caves, including more than 400 caves of all sizes that have been discovered and surveyed. Inside the pristine forests are the habitats of the Arem ethnic group, who once lived in the stone caves for many years. Phong Nha - Ke Bang possesses rich and diverse values ​​and resources.

The name Phong Nha - Ke Bang is a combination of the names of the Phong Nha village located at the forest entrance and Ke Bang, the name of an ancient village deep in the western limestone mountains of Quang Binh province. The merging of these two names symbolizes the vast coverage of this national park.

Phong Nha - Ke Bang Cave System

During the war, many caves in the Phong Nha - Ke Bang area were used by the Vietnamese military as storage for weapons and supplies, and some served as living and hiding places during air raids. However, the cave system in the Phong Nha - Ke Bang area only became widely known when the cave exploration team from the UK, led by Howard Limbert, collaborated with the geography department of the University of Natural Sciences, a branch of the Hanoi National University, to conduct dozens of surveys from 1990 to the present.

As of 2022, after 32 years of exploration, the expedition has discovered, surveyed, and mapped more than 404 caves, with a total length of all caves reaching 220km. Despite discovering and surveying many caves in the past 32 years, cave experts estimate that only about 30% of the area of limestone mountains in Phong Nha - Ke Bang has been surveyed. Surveying work is still carried out annually to find new caves.

The limestone caves are formed along three main river systems inside the limestone mountains, including the Phong Nha Cave System - with caves such as En Cave, Lanh Cave, Khe Ry Cave, Son Doong Cave, Thung Cave, Va Cave, Water Crack Cave, and finally, Phong Nha Cave. The Vault Cave System - Ruc Ca Roong Cave, 35 Cave, Pygmy Cave, About Cave, Tiger Cave, Dai Cao Cave, Ba Cave, Tron Cave, Sang Cave, Vinh Dai Cave, Vault Cave, and Paradise Cave. The Water Mooc System - Khe Rung Cave, Ky Vuc Cave, Ha Hai - the Water Mooc system has a large flowing water source, but explorers have yet to find caves connecting the Mooc Water to valleys deep in the limestone mountains, such as Hung Xuong and Hung Tri."

Source: https://oxalisadventure.com/vi/cave/hang-son-doong/
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