MaryAnne Shults's Blog

March 15, 2011

Halong Bay: Forget the dragon tale, it's all about geology

p>One of my former geology professors said the best examples of geology existed in California and in the Western United States. Death Valley, with its mysterious sliding rocks, Mojave Desert offers “rock jocks” the chance to study all three rock types, and lastly, the Colorado Plateau contains three geological wonders – now national parks – the most well known is the Grand Canyon.

Halong Bay, VietnamJunk boats cruise through Halong Bay among the vast limestone pinnacles that jut from the teal-colored gentle water.

I have to thank my instructors who have passed on their passion to me as I’m more of a geology hobbyist. This week I experienced one of the most beautiful examples of the combination of plate tectonics, sedimentary layering I’ve ever seen, set in the beautiful Halong Bay in northeast Vietnam. The area is acclaimed as a UNESCO World Heritage Site of international geomorphological significance.

On the three-hour drive from Hanoi to Halong Bay on bus overcrowded with piles of luggage, 14 of us from Cal State Fullerton ventured to the Quang Ninh province, passing redundant hectares of rice paddies often being tended to by farmers in high black rubber boots in their traditional conical hats, often with the aid of a water buffalo hooked to a plow.

In the center of some of the paddies are large burial tombs. Because of beliefs tied to Vietnamese animism, it is traditional to bury loved ones on family-owned land, where the deceased becomes an ancestor whose spirit protects the family. Farmers also believe burying the dead on home soil helps discourage outsiders from buying their land.

Suddenly the landscape changes when large pinnacles of oddly shaped foliage-covered limestone peaks occur in the distance, almost ghostly from the constant fog. The once nearly-flat landscape morphs into a mountainous jungle of green.

The jungle gives way to scattered newly-constructed high-rise modern hotels, indicative of the expanding tourism of the area. The sharp air of the ocean permeates my nostrils signaling that Halong Bay is nearby.

The harbor is full of tourists and vacationing locals. We drag our luggage along a jetty with broken and somewhat threatening concrete steps that lead down to a flat boat that will carry us to one of the many multi-passenger junk-style ships anchored several hundred yards out into deeper water that would host our two-day cruise through the bay’s 1,769 islands.

Once on board our temporary home, we explored the ship. Old, yet sturdy, it was as though the clock had been turned back. The sleeping quarters consisted of two single bunks with a meager but freshly-painted nightstand. The tile-floored tiny bathroom had a sink and toilet, and the shower consisted of a hand-held shower head hanging on the wall; no shower stall. A bit odd, but completely functional.

As we headed out of the harbor and into the bay, and the tiny crew prepared lunch, most lounged on the front deck, the photographers ready with their talented eyes to catch the perfect shot. After over a week of overcast skies, the ghostly fog lifted, the clouds parted and the sun peaked through, its rays shimmering on the teal-colored, calm water. We were heading to Hang Sun Soon Cave, one of the area’s most spectacular geological miracles.

We passed a floating fishing village with children running along the dock, shouting as their parents quickly headed in our direction in small rowboats burdened with fruit, vegetables and fresh fish to hawk their wares.

Halong Bay, VietnamAs the sea rose and fell, over millions of years, shelled sea creatures died and sunk to the bottom, the weight of the layering compressing and eventually creating limestone. At one time, these were all horizontal layers, now lifted and folded due to movements (tectonics) of the Earth's continental crust.

Back to geology.

“Ha Long” means “where the dragon descends into the sea” and folklore says that the islands were created by a dragon plunging into the sea who whipped around his tail, cutting out the islands. Science debated legend; it’s all about geology.

About 500 million years ago this area of Vietnam was a deep sea, submitted to the constant activity of tectonic plates, which underwent periods of inverse-motion that created mountains deep under the water. The tectonic activity raised the entire region from the depths, and making the sea warm and shallow, for the next 100 million years or so.

The islands of Halong Bay are all cut in sequences of folded finely-grained limestone created about 300 million years ago when the area was covered by a warm, shallow ocean. Land masses were covered with lush, tropical jungle. Some are more than 1000 meters thick. This type of limestone is ideal for the formation of karst, or landforms shaped when water dissolves layers of this soluble bedrock.

Karst landforms are generally the result of mildly rain acidic water containing carbonic acid that begins to dissolve the surface along cracks or bedding planes. Over time, these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features.

Marine erosion has played a factor during its geological timescale. Repeated rising and falling of sea level, called regression and transgression, is when an area is covered by sea water, then dries up; rinse and repeat, so to speak. Currently, it is why one sees erosion at the bottom of the islands and pinnacles, hence some appear to be top-heavy, balancing precariously as the salty sea water undercuts through systems of cracks and fractures. While kayaking around the islands, we saw where rainwater had begun formation of small marine notch caves in their infancy that would never reach maturity as the sea would dissolve their adulthood.

Some of the caves are large and vast. We visited Hang Sung Sot cave, one of the largest on Bo Hon Island.

From the entrance, we entered the first chamber up a staircase cut into the rock under a lush canopy of green vegetation. At the side of the entrance, the rock seems to form the shape of a horse with a long sword. Legend has it that Thánh Gióng, dubbed a saint, chased away evil spirits and demons. After this feat, Saint Gióng flew to heaven, leaving a stone horse and sword to continue to keep the demons away.

Stalactites hang from the high ceiling, about 100 feet high, in a variation of forms and shapes. Multi-colored lighting take away from the natural beauty, giving it an almost Disneyland-like feel. Once into the second chamber, the ceiling appears more sandstone, filled with large concave dips.

These beautiful grottoes and the area in general make the photos in geology textbooks truly three dimensional – just enough to make just about anyone a “rock jock.”