This is part two of a five-part series on the natural wonders of Mulu.
Mulu National Park is a geological marvel, featuring extensive karst landscapes and unique cave ecosystems. Responsible management is essential to balance tourism and conservation, ensuring that these natural wonders are preserved for future generations while educating visitors about their ecological importance.
Mulu’s Karst Wonders and the Future of Cave Conservation
For a geologist, Mulu National Park is a natural marvel where Earth’s processes are vividly on display, revealing secrets shaped over millions of years.
Mulu’s intricate limestone caves, towering karst pinnacles, and sprawling underground rivers are not just breathtaking — they are a rare and invaluable geological record of the planet’s history.
Associate Professor Dr Dominique Dodge-Wan, Programme Coordinator of Applied Geology at Curtin University, describes Mulu as an extraordinary intersection of geology, climate, and biology.
She said the park’s limestone formations, which are both thick and pure, combined with abundant year-round tropical rains and lush vegetation that produce carbon dioxide, create an ideal environment for karstification.
Karst is a type of landscape formed by the dissolution of soluble rocks — most commonly limestone, dolomite, and gypsum.
On another note, karstification is a process that slowly transforms solid rock into elaborate cave systems and dramatic landscapes.
“For geologists, Mulu offers an unparalleled field lab where the complex interactions of water, rock, and time can be studied in a setting largely untouched by human activity.
“In Mulu, we see karst at its most extreme — a living example of geological forces at work, preserving ancient climates, delicate ecosystems, and spectacular landforms,” she told Sarawak Tribune.
Karst Formation Fundamentals
Dominique said karst formations refer to unique landscapes shaped by the dissolution of rock both above and below the ground.
Scientifically, the process of karstification begins when rainwater absorbs carbon dioxide from the atmosphere and soil, thus forming a weak carbonic acid.
When this slightly acidic water seeps into the ground, it gradually dissolves soluble rocks, particularly limestone, through a process called chemical weathering.
“Over time, this dissolution creates underground voids, forming distinctive landscapes featuring sinkholes, disappearing rivers, and extensive cave systems.
“In typical karst regions, most streams and rivers flow underground rather than on the surface, eroding the bedrock over thousands or even millions of years, thus forming complex networks of caves and underground drainage systems,” she explained.
Dominique pointed out that the term “karst” originates from “Kras”, a plateau in the Dinaric Karst region along the Adriatic Sea, spanning from Italy in the northwest through Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, and Kosovo to Albania in the southeast.
This area, known as the “classic karst”, became a pioneering study site for karst landscapes where geologists first defined and categorised these landforms and processes.
“The Kras Plateau exemplifies a limestone landscape with an extensive sequence of carbonate rocks, which allows the rock to withstand extensive dissolution and form monumental cave structures,” she said.
Dominique highlighted that climate influences karst landscapes, particularly in tropical regions like Mulu, where rainfall occurs frequently and often exceeds 2,500mm annually.
“This high and constant rainfall drives the intense karstification seen here in Mulu, feeding the acidic water that shapes Mulu’s limestone, thus creating expansive and intricate cave systems,” she said.
Scientific Importance of Karsts and Caves
Caves represent unique ecosystems, hosting specialised fauna and flora adapted to varied conditions of temperature, lighting, humidity, and limited food sources — species often found nowhere else.
Dominique said these are environments unlike any on the surface.
“The diversity within a single cave — from the entrance to the dark zones — creates microclimates that allow unique life forms to thrive,” she said.
From a geological perspective, Dominique said that caves serve as time capsules, preserving sediments and speleothems that record ancient climates, rainfall patterns, and volcanic activity, sometimes dating back millions of years.
Sediment refers to solid material that is moved and deposited in a new location, whereas a speleothem is a geological formation created by mineral deposits that accumulate over time in natural caves from dripping or slowly flowing water.
“These natural archives offer us an invaluable glimpse into Earth’s past, as karsts and show caves serve as critical laboratories for studying ancient conditions. There is still so much to discover, as caves hold complex ecosystems and geological records that have barely been touched by science,” she said.
Uniqueness of Mulu’s Karst and Epigene Caves
Mulu’s karst landscape is classified as “extreme karst”, a term developed by Tony Waltham in 2005 to describe the highest degree of karstification found exclusively in wet tropical environments.
Dominique said that several factors contribute to Mulu’s exceptional nature, particularly its extensive cave passage length and remarkable cave sizes.
“This uniqueness stems from a combination of geological, climatic, and biological factors that support one of the world’s most complex and vast karst systems.
“Mulu features limestones that are over 2,000 metres thick and characterised by remarkable purity, meaning they contain minimal impurities and fewer bedding planes. This purity and structural strength allow the rock to withstand extensive dissolution, enabling the formation of monumental cave systems,” she explained.
Mulu’s unique geological setting includes the famous Mulu Pinnacles, which are tilted rock formations — an image that can be found on the RM100 note alongside the iconic Mount Kinabalu summit.
Mulu’s limestone cave system also receives surface water flowing in from the adjacent sandstones to the southeast.
At the same time, Dominique said that Mulu’s karst landscape features prominent landforms such as tower karst and cone karst.
“Tower karst develops with isolated, vertical cliffs and complex cave networks, often containing expansive chambers, tall pinnacles, and extensive dissolution at various levels.
“As the karst landscape’s base level lowers, these systems become rejuvenated, forming a layered, three-dimensional cave structure. While large chambers exist in other climates, Mulu’s tropical karst is particularly known for its scale,” she said.
Dominique said that Mulu’s caves exhibit fascinating interactions between biological and geological processes.
Large cave entrances create extensive twilight zones with gradual changes in light and temperature, promoting the growth of phototropic stalactites and the formation of photokarren — sharp rock projections created by cyanobacteria in low-light areas.
Additionally, rare crayback stalagmites develop under similar conditions, influenced by light-dependent microorganisms.
Stalagmites are generally shaped like mounds or tapering columns rising from the floor of a cave, formed from calcium carbonate crystals deposited by dripping water and often uniting with a stalactite above to form a column.
“This dynamic interplay of biological and geological processes in Mulu’s caves provides an extraordinary area of study, with significant research potential still untapped,” she said.
Dominique pointed out that Mulu represents the pinnacle of tropical karst, showcasing an incredibly complex cave system, giant skylights, towering pinnacles, and expansive twilight zones where rare photokarren and crayback stalagmites may be found.
“It stands as a world-class example of tropical karst, with many more discoveries awaiting in its depths,” she added.
Developing and Managing Show Caves Responsibly
As interest in eco-tourism and natural wonders grows worldwide, show caves like those in Mulu National Park are attracting increased numbers of visitors.
However, managing access to these ancient landscapes requires a careful approach to avoid damage and preserve their beauty and significance for future generations.
Dominique explained that responsible show cave management must balance conservation with public access.
“Caves are fragile environments and we need to protect both the inside of the caves and the surrounding karst and non-karst landscape. Mulu’s caves, known for their dramatic limestone formations and underground rivers, are situated within a complex and sensitive karst system.
“The surrounding environment, including cave entrances and surface areas, needs as much protection as the cave interiors. This includes safeguarding the extensive drainage systems, which support the unique ecosystems above and below ground,” she said.
To manage the impact of tourism, Dominique suggested that visitor numbers be carefully controlled, as each cave has a unique carrying capacity.
By limiting visitor numbers, the park can reduce wear on the cave floors, walls, and delicate formations, which might otherwise suffer from damage such as graffiti, breakage, or litter.
“Another critical aspect is maintaining the cave’s natural microclimate. In sensitive caves, even slight changes to temperature, humidity, or airflow can disturb the ecological balance.
“For instance, the renowned Lascaux caves in France suffered when the introduction of humidity and carbon dioxide disrupted the delicate fungal and microbial populations. Artificial lighting can also cause plants to grow in dark cave zones where they are not naturally found.
“In Mulu, lighting is kept to a minimum and is used only for short durations to enhance visitor safety and experience while minimising alterations to the cave’s natural conditions,” she said.
In addition to these precautions, Dominique stressed the importance of education, as well-informed guides play a key role in communicating conservation efforts to visitors.
She said that information panels, brochures, and trained guides help visitors understand how they can minimise their environmental impact while enjoying the caves.
“Tour guides are more than just storytellers — they are stewards of the caves,” she said.
At the same time, Dominique pointed out that infrastructure must also be thoughtfully planned and maintained.
She said that essential facilities, including gates, paths, railings, and lighting, must be installed with the cave’s preservation in mind.
“Periodic maintenance helps reduce long-term environmental impacts and keeps the experience enjoyable for tourists. Continuous environmental monitoring is also important to track changes in parameters like temperature, humidity, and carbon dioxide levels,” she said.
The involvement of the local community in show cave management is another essential factor.
Mulu’s caves hold cultural significance, and collaboration with nearby communities ensures that the benefits of tourism flow back to the locals who have historically depended on the land.
“We must remember that caves like Mulu’s are not just geological formations; they are part of the local culture and history. Involving the community helps us protect both the land and its legacy,” she said.
With visitor interest on the rise, Dominique stressed that a thoughtful and science-backed approach is essential for sustainable tourism.
“Through proper management, we can share these incredible natural wonders with people from all over the world while still preserving their beauty and integrity for generations to come,” she explained.
The Road Ahead
The journey to balance conservation with increasing tourism in Mulu’s caves is complex but crucial.
With visitor interest rising, safeguarding these delicate ecosystems without restricting public access requires innovative approaches and dedicated management.
Dominique reiterated the importance of careful management in welcoming large numbers of visitors while protecting these sensitive environments.
“For fragile caves, advanced solutions such as virtual tours can offer a meaningful alternative, using 3D filming and scanning to replicate the experience without physical impact. These virtual visits could not only bring the cave’s beauty to a broader audience but also make it accessible to those with mobility limitations or who are unable to physically visit the caves,” she said.
As gateways to learning, Dominique said, Mulu’s show caves present an invaluable resource for educating the public on the importance of conservation.
In these spaces, quality signage, educational materials, and multilingual guides highlight the ecological value of the caves and the interconnected biological systems they support.
For younger generations, she said, educational outreach through field trips and school programmes fosters an early appreciation for the intricate balance between preservation and exploration.
“The impact of starting these conservations early can’t be overstated. It shapes the next generation’s view on conservation and how we interact with natural environments,” she said.
Despite these conservation efforts, the world’s karst landscapes still face external threats beyond visitor numbers.
Dominique said that changes in land use, limestone quarrying, water pollution, and climate change are among the most significant risks.
She said the effects of such factors could extend far beyond the caves themselves, impacting local watersheds, flora and fauna, and even the stability of surrounding rock formations.
“Responsible land use and legislative protection are essential to safeguarding these unique environments against irreversible damage. Additionally, climate change brings concerns over temperature shifts, altered rainfall patterns, and the potential for flooding — all of which could disrupt the delicate ecological balance within the caves,” she said.
Noting that the future for Mulu’s karst systems is both exciting and challenging, Dominique said it calls for a commitment to both innovation and preservation.
“Our goal must be to prioritise awareness over profit. Cave conservation isn’t just about the physical preservation of these spaces; it’s about fostering public understanding and respect for their fragility,” she said.
With a combination of scientific research, sustainable tourism practices, and community collaboration, the future for Mulu and other karst regions holds promise. These extraordinary caves and karst formations can continue to inspire awe and wonder, standing as a testament to the power of nature and everyone’s role in protecting it.
