A bird's eye view of Thailand's topography and how it was shaped over time.
The physical and political divisions of Siam, later named the kingdom of Thailand (in 1939), as charted on the Indo-China map by Edward Stanford in 1904. Image credits: David Rumsey Historical Map Collection.
Dear Reader,
I’m sure some of you have travelled to Thailand to partake of its rich culture, incredible cuisine, vibrant nightlife, and tourist destinations.
As a tourist, you would have researched the sights and sounds, the tastes and treasures that the country has to offer, and perhaps, even the history of the only uncolonised Southeast Asian nation. I wonder how much geography surfaced during your research. In so many ways, the geography has profoundly influenced its history and culture. Thailand’s strategic location at the crossroads of trade routes facilitated the exchange of goods, ideas, and cultures. The Malay Peninsula connecting to the South China Sea enabled Thailand to be a maritime hub. Fertile plains irrigated by the Mekong and the Chao Phraya rivers supported extensive rice cultivation, and enabled the rise of a powerful kingdom — which traces its ancestry to India, and the country’s traditions stem from the Ramayana lore.
Last month, I had the chance to travel to Bangkok for work. As with work trips, there was little time to read about or appreciate the finer details of the country. I’ve caught up since, and this edition hopes to distil how Thailand’s geographical features have presented opportunities and challenges in shaping the little nation.
Thailand’s Topography
From the air, the deltaic capital of Bangkok appears like a flat, colourful tapestry of farms and factories, with an intricate network of shimmering canals, interspersed with urban infrastructure such as residential complexes, massive flyovers and bridges. On a clear day, one can see the Chao Phraya river snaking across the landscape, towards the Gulf of Thailand. As you approach the airport, especially if you’ve been flying from the west, you might see the ornate spires of temples that embellish the capital.
To the west, Thailand is bound by Myanmar (formerly Burma), its bitterest enemy through history — from the 16th - 19th CE, the multiple invasions, sieges and retreats of the armies of these Indo-Chinese territories, have gone down in history as the Burmese-Siamese or the Yodian wars. To the west and east lies Laos, a territory ceded to the French, in a strategic compromise to maintain sovereignty. (For a more detailed historical note, read The Uncolonized: Thailand by Geoff Gibson.) To the southeast lies Cambodia — a territory that shared Thailand’s history under the Khmer Empire, writ large in the incredible, concentric-walled temples strewn across both countries. The southwestern corner of Thailand is part of the Malay Peninsula, hemmed in by the South China Sea. The Malay Peninsula is also close to the Andaman archipelago.
A shaded relief map of Thailand clearly shows the folded mountains, the vast flat river plains, and part of the Malay Peninsula stretching into the Gulf of Thailand. The textured portion to the right is the Khorat Plateau. Image credits: Miguel Valenzuela, MappedOut.
Thailand’s topography is defined by five distinct features: folded mountains dividing Thailand from Myanmar and Laos, the Khorat plateau — a low tableland irrigated by rivers to the northeast, the braided, sinuous Chao Phraya river basin at the centre, the Gulf of Thailand, and the Malay Peninsula. Interestingly, the fold mountains along the Thailand-Myanmar border were created during the same uplift processes that gave rise to the Himalayas. The upliftment continues further south and ends in northern Malaysia. Thailand’s long granitic ridges formed when molten rock pushed through old sedimentary layers.
Thailand’s farmlands are largely irrigated by the Mekong and the Chao Phraya rivers. The Ping, Yom and Nan rivers carve out narrow valleys before merging with the Chao Phraya, and carry rich alluvium from the mountains to the plains, making them fertile. Some of the rivers also serve as navigation channels. The Chao Phraya braids its way to the Gulf of Thailand and creates a series of tidal flats and mangrove swamps along the southern coast.
Karst Landscapes & Lakes
Between 286-245 million years, during the Permian Period, light-grey, fossil-bearing limestone was deposited along the southern peninsula of Thailand. Over time, rainwater has sculpted this limestone into a variety of spectacular features from stalactite and stalagmite-rich caves, coastal towers and stacks, and bright turquoise lakes.
Thailand’s major tourist attractions, like Khao Sok National Park with the beautiful Cheow Lan Lake, Phang Nga Bay, Krabi and Phuket islands, are located in karst topography — a landscape defined by limestone, formed when calcium carbonate is precipitated by chemical processes. I’ve written about karst formations from India, and the Philippines in previous editions, as also how these landscapes are etched by the rain.
The distinct jagged landscape that belies a karst topography, as seen from the Ratchaprapha lake at the Khao Sok National Park. Image credits: BerryJ, CC BY-SA via Wikimedia Commons.
The Tiger Cave monastery in the province of Phang Nga, I hear, has a Buddhist temple built under a karst overhang, accessible only via a near-vertical stairway perched on a limestone ridge, surrounded by a tropical rainforest. The Buddhist monks place offerings and statues in smaller caves — another example of geological formations that inspire veneration.
There is no soil in karst caves. Over the years, insect and fruit-eating bats dwelling in these dank caves leave a rich layer of poop — this nitrogen-rich guano forms the base nutrient for karst ecosystems.
This unique aspect of karst limestones has resulted in a high degree of endemism — species that are geographically restricted and exist nowhere else on the planet. Endemism is an ecologically interesting phenomenon, where species evolve in unique, often adverse conditions. Yet endemism is often the quickest path to extinction.
The world’s only known amphibious centipede, Scolopendra cataracta, was discovered near the Khao Sok National Park in 2001, and declared as a separate species in 2016.
Original image: Warut Siriwut, Gregory D. Edgecombe, Chirasak Sutcharit, Piyoros Tongkerd, Somsak Panha; crop by EdChem, CC BY via Wikimedia Commons.
Thailand’s karst landscapes host over 100 endemic species across taxa; cave crickets, centipedes, whiptail spiders, blind caecilians, near-blind fish, rodents, and many more species than we can imagine. The labyrinthine cave network often isolates species, which radiate into numerous others. For instance, a 2011 study documented six highly differentiated genetic lineages of a particular rodent, Leopoldamys neilli, each corresponding to a particular region of Thailand. Over time, these lineages have been isolated, and the genetic flow between them slowed down. This is particularly surprising as geographically, these populations were sampled very close to each other.
Geopolitically, Thailand’s bid to be seen as a progressive state meant a period of rapid modernisation. Yet in 1988, Thailand realised just how detrimental their timber logging operations had been to their fragile rainforests. The Kingdom of Thailand issued an absolute ban on logging, and the industry turned from timber to concrete.
A key component of concrete is limestone, preferably with a good magnesium content. Carbonate rocks are prone to a process known as dolomitization, where calcium ions are replaced with magnesium. The resultant feature is known as a dolomite. Since then, numerous karst landscapes across Thailand have been dynamited for construction, and one can only imagine, how many unique cave ecosystems have been lost.
Ko Tapu (Tapu Island) in the Phang Nga Bay, in Thailand, may seem familiar. It was the location that featured in the James Bond film, The Man with the Golden Gun. Image credits: Diego Delso, CC BY-SA via Wikimedia Commons.
Karst landscapes are not only vital ecosystems for endemic biodiversity but also massive reservoirs of water. Rainwater, not only carves limestone into wondrous shapes, but it is also stored with fractures, holes, and caverns. Sometimes, collected rainwater bursts out of caves as underground rivers. I’d written about karst’s ecosystem function when I wrote of such landscapes in the Philippines. Yet what’s more incredible is that by soaking up excess rainwater like a sponge, karst landscapes can also prevent flooding. The stored rainwater is gently released throughout the year and can help mitigate droughts.
Not just in Thailand, karst landscapes are under threat in so many geographies, their ecosystem services unappreciated, and the biodiversity understudied. I can only hope that through sensitive, community-centric tourism initiatives, and more research, we can better preserve this fragile, invaluable geoheritage.
Further reading: The 1999 paper by Vermeulen and Whitten has recommendations for limestone quarrying management, with insights on how to conserve isolated structures versus larger stretches.
River Systems & Bangkok Clay
Around two hundred kilometres north of Bangkok, the Ping, Wang, Yom and Nan rivers join together to form the Chao Phraya river, Thailand’s most important watershed. The Chao Phraya river network irrigates nearly 35% of the country and is integral to the country’s economy, as it passes through major urban cities and the rice bowls of Thailand such as Chainat, Angthong, Sing Buri and Suphan Buri. A languid, meandering river, the Chao Phraya makes its way across a flat, featureless plain, forming an extensive delta of marshy tidal flats, before draining into the Gulf of Thailand.
Interestingly, none of the tributaries of the Chao Phraya river, extend beyond the country’s present-day geographical limits, indicating how crucial the watershed was in the politico-geographic history of the nation. Image credit: Kmusser, CC BY-SA, via Wikimedia Commons.
In the late Pleistocene (between c. 129,000 and c. 11,700 years ago), the Chao Phraya River and its tributaries shaped the central part of the country by bringing in sand and clay, which settled and hardened over time. The surface of this layer even has iron-oxide patches that show it was once part of a flowing river environment.
During the Holocene period, the last 10,000 years or so, when the Chao Phraya river had eroded the basin almost to the level of the sea, its interaction along its salty margins changed. Roughly 6,000 years ago, the sea level was about 4 meters higher than today. It wasn’t until about 1500 years ago that the sea dropped to its current level. This changing sea level helped create the delta, an area rich in soft marine clay, known as Bangkok Clay. At present, the city of Bangkok sits just about 1.5-2 meters above sea level. Yet it lies over rich clay deposits, some of which are as deep as 2000 meters!
These soft clay deposits play a big role in land subsidence and cause the ground to slowly sink into the sea. Land subsidence is further exacerbated by excessive groundwater extraction — for the past few decades, Bangkok’s development has relied heavily on deep well water. As the city lies close to the sea, excessive pumping of its groundwater reserves also leads to saltwater intrusion - where seawater infiltrates land-based aquifers and contaminates freshwater reservoirs. Along the Chao Phraya’s deltaic fringes, coastal erosion is also a major concern, as land is being gradually worn away by the tides.
The Chao Phraya river has been a mixed blessing in shaping the country’s landscape, economy, and environment, and is undeniably Thailand’s key geographical feature.
Bangkok’s skyline of temple spires and high-rises as seen from the Chao Phraya ferry. Image credits: Devayani Khare.
There is so much to write about the Malay Peninsula, bounded by the Strait of Malacca, where some of the world’s most dangerous pirates sail, which acts as a geographic barrier for marine organisms between the Indian Ocean, and the South China Sea. Yet I fear this edition has gotten too long to hold your attention, and I will need to draw a line somewhere, with the hope that I can give these tantalising topics the space they deserve soon.
Khàawp khun kha (thank you in Thai),
Devayani