The Pitch Lake of Trinidad and Tobago

BY AWAKE! WRITER IN TRINIDAD

WHAT do Hong Kong’s Cross Harbour Tunnel, Austria’s Transalpine Highway, and England’s Jubilee Way Viaduct have in common? They have all at some time been paved with a mixture containing a unique asphalt *​—one that comes from the Pitch Lake of Trinidad and Tobago.

The great Pitch Lake is a natural surface deposit of asphalt. In 1814 one geographical dictionary described it as “a most wonderful phenomenon.” See for yourself as we pay a visit to its location near the southwestern coast of Trinidad.

 A Walk on the Lake

As we enter the village of La Brea (Spanish for “the pitch”), we notice that sidewalks appear to be sinking into the ground. Even some houses are strangely misaligned, as if they were buckling under their own weight. We have little time to wonder why this is the case, for stretching before us is something that looks like an immense abandoned parking lot. We have reached the Pitch Lake. Our guide informs us that the lake covers approximately 115 acres [47 ha] and is about 250 feet [80 m] deep at the center. “Let’s have a closer look,” he suggests.

We gingerly take our first steps on the lake and find that its surface is unexpectedly solid, although uneven. In fact, the lake can easily support the weight of a truck and other heavy machinery! (These would, however, slowly sink if left for a long time in one spot.) We must watch our step, though! In the midst of this terra firma, there randomly occur small patches of sticky bitumen that can present the unsuspecting visitor with an unpleasant and gooey surprise.

Since our arrival, we have caught occasional whiffs of a pungent odor. “Hydrogen sulfide,” we are told. Small amounts form in the lake, together with methane, ethane, and carbon dioxide. Our guide breaks open a lump of asphalt, and we see that it looks like Swiss cheese​—full of holes formed by trapped bubbles of gas.

The Pitch Lake is also an important wildlife habitat. Some pools of water that collect on its surface and in the grassy fringes around it are home to the rare masked duck (Oxyura dominica). Likely, we will not see this small bird today, as it often remains motionless or silently submerges when approached. When we walk past some chest-high grasses, up flashes another bird, the wattled jacana (Jacana jacana). Its dark body is a contrast to the pale yellow beneath its wings. The purple gallinule (Porphyrula martinica) and other marsh-dwelling  species are also found here. Small freshwater fish inhabit the aquatic areas, and caimans are occasionally seen.

Used for 400 Years

Pointing toward the coast, our guide relates that in 1595, British explorer Sir Walter Raleigh anchored in this area. At that time the lake, which now lies in a low depression, was a level plain with streams of asphalt reaching to the coast. Raleigh used the asphalt to caulk his leaking ships and declared it to be “most excellent good,” noting that it “melteth not with the sunne as pitch of Norway, and therefore for shippes trading south portes very profitable.” *

In 1846, Canadian Dr. Abraham Gesner, later dubbed the Father of the Oil Industry, distilled a new illuminating oil from Trinidad’s asphalt. He called it kerosene. Unfortunately, the sulfur in this asphalt gave the oil a rather disagreeable odor. Gesner later found another source of asphalt that was essentially odorless.

Trinidad’s lake asphalt really came into its own when its value for paving roads was discovered. In 1876, engineers suggested that it be used to pave Pennsylvania Avenue in Washington, D.C. Despite heavy traffic, the pavement reportedly remained in excellent condition for 11 years. This helped to establish the reputation of Trinidad’s asphalt.

In recent years oil companies have been able to produce cheaper bitumen as a by-product of petroleum refining. Yet, engineers have continued to use Trinidad’s natural asphalt in building highways, bridges, airports, and seaports. Why?

A Unique Blend

When included in paving mixtures, this asphalt is known to impart strength, durability, stability, and nonskid properties to the paved surfaces​—not to mention a mat-gray finish that enhances visibility for night driving. Lake asphalt has been successfully used for road surfaces where temperatures exceed 100 degrees Fahrenheit [40°C] in summer and fall below minus 20 degrees Fahrenheit [-25°C] in winter. Airport runways built with this asphalt have performed well, in spite of the stresses placed on them by the constant takeoff and landing of heavy aircraft. These pavements are also resistant to degradation from deicing fluids as well  as fuel and oil leaks. Many of these paved surfaces have lasted more than 20 years with little or no maintenance.

The characteristics of Trinidad’s lake asphalt have been attributed to its special composition. The bitumen in it is composed of 63 to 67 percent malthenes and 33 to 37 percent asphaltenes. Malthenes are a class of sticky petroleum chemicals that give bitumen its adhesive properties. Those present in this lake asphalt have been described as “extremely sticky and cementitious rather than oily, as in the case of certain [refinery-] derived bitumens.” Asphaltenes are another group of hydrocarbons that help to make bitumen a thermoplastic material​—one that softens and flows when heated and hardens as it cools. The character and relative proportions of all these components give the asphalt properties that are not easily duplicated by refineries.

Mining and Refining

The rumble of heavy machinery draws our attention, and we turn to see mining equipment driving onto the lake. This is basically a huge tractor fitted with strong metal tines, or prongs, that rip asphalt from the lake’s surface. The fragmented asphalt is then loaded into cable-drawn railcars for transport to a nearby factory. Well over nine million tons of asphalt have been mined from this site since the late 1800’s! At the current rate of consumption, the estimated ten million tons that remain are projected to last another 400 years.

After several tons of asphalt has been removed from the lake, the hole that was formed shrinks and disappears within a few weeks. This gives the impression that the lake replenishes itself. However, the “solid” asphalt is really a very viscous fluid and adjacent material simply flows into the depression. The entire lake is thus in a state of constant but imperceptible motion.

Do you remember those tilted houses that we saw earlier? Their displacement is partly due to subterranean veins of asphalt that extend outward from the lake. People who build in this area must choose their location carefully.

“Let’s go up to the factory,” our guide suggests. The refining process is really quite simple. The raw asphalt is dumped into large vats, each with a capacity of over 100 tons. Here the asphalt is melted by coils of pipe carrying steam that is heated to about 330 degrees Fahrenheit [165°C]. This liberates trapped gases and drives off the excess water that constitutes about 30 percent of the raw asphalt’s weight. Next, the asphalt is screened to remove bits of wood and other vegetable matter. Finally, the hot asphalt is drawn off into fiberboard drums lined with silicone paper. The drums are made right here at the factory, and each holds about 530 pounds [240 kg]. The entire refining process takes approximately 18 hours.

“The purified asphalt is called Epuré,” says our guide. It blends readily with refinery bitumen and other materials to produce high-performance paving mixtures. In recent years it has also been used to make a variety of paints, as well as cementing, insulating, and waterproofing products. Thus, it has found its way into many homes and buildings around the globe.

One author summed matters up well when he wrote: “There is something of a peculiar . . . interest which seems to hover over this wonderful work of God, filling the student of nature with awe and admiration.” Yes, the Pitch Lake of Trinidad and Tobago is truly a fascinating place to visit!

[Footnotes]

Petroleum, or crude oil, when evaporated leaves a residue composed almost entirely of bitumen. Petroleum-derived bitumen is also called asphalt. However, in many places “asphalt” refers to bitumen mixed with mineral aggregates like sand or gravel, often used in the paving of roads. For the purpose of this article, “asphalt” refers to either the crude or the refined product from the Pitch Lake.

[Picture on page 24, 25]

The Pitch Lake is a natural surface deposit of asphalt

[Picture on page 26]

An asphalt refinery

[Picture on page 26]

Mining asphalt from the lake