As you drive south from Riyadh, the capital of Saudi Arabia, toward al-Kharj, the rocky desert is dotted with large circular areas of lush green grass. Pivot-point irrigation makes it possible to grow fodder here, in the middle of the desert, for some of the world's largest dairy farms nearby. The water is "fossil water," pumped from vast natural underground reservoirs filled more than 7000 years ago, when Arabia's climate was wet and verdant. (See Aramco World, March/April 1980.) In some places near al-Kharj, this water comes close to the surface, and sinkholes (dahl in Arabic) measuring some 20 meters (65') in diameter have opened in the ground.
As a diver and adventurer, I had been fascinated with these holes for years. I had fantasized that a complex underwater cave system might lie here, waiting to be discovered. But the several sinkholes I had seen all had steep 60-meter (200') walls dropping down to the water—an impossible descent with SCUBA equipment.
In 1994 I was invited to visit some caves "discovered" almost 15 years ago by two American cavers, John Pint and Dave Peters. (In Saudi Arabia, every natural feature, even those that may seem quite insignificant to Westerners, has long been named by local bedouins.) Pint and Peters, then teachers in Dammam, had seen an aerial navigation map showing many holes near the little town of Ma'aqala, 75 kilometers northeast of Riyadh. Considering that very few limestone caves had been found in Saudi Arabia, they became very excited at the prospect that these holes might be the entrances of unexplored caves.
When they investigated on the ground in 1983, they found an area like Swiss cheese, with holes everywhere leading down to caves. Pint stumbled on the biggest cave—literally—when he tripped and fell on a tiny hole and felt a damp wind blowing in his face. The extent of that cave is still not known, though several kilometers of it have been explored, and Pint has named it Dahl Sultan, in view of its size. My interest in these caves, of course, was to find out if there was diving to be done there.
Pint and some of his friends and I located the caves again in 1994, and found in one of them camel bones, gazelle horns and ostrich feathers, indicating that ancient hunters might have lived or sheltered there.
The entrance to Dahl Sultan itself was only big enough for one person to squeeze through at a time, but it opened into a magnificent room with beautiful stalactites. Tunnels led on through a succession of rooms for as far as we dared to walk. This cave, created by running-water erosion of the limestone rock, did not extend very far below ground level. It apparently is regularly flooded in the winter, and its sandy floor was damp, but it was not deep enough to reach levels that might contain standing water. Diving would have to await the discovery of other caves.
Unfortunately, it was through a tragic accident that I learned at last of a cave that contained water and was also accessible to divers. At Ain Hit, the limestone wall of the Sulaiy Escarpment is punctuated by a huge hole known as Dahl Hit. This cave leads down to an underground lake 100 meters (330') below the ground. I read about it in a SCUBA club newsletter after a diver equipped only with mask and flippers lost his way in the underwater cavern and drowned. As far "as I could find out, however, nobody had tried to explore Dahl Hit using breathing equipment, so I began planning an expedition. Little did I know that it was the start of two years of incredibly hard, fascinating work.
Cavediving has grown, over the last 20 years, into a specialized sport in its own right. The cavediver's need for extended time underwater has spurred the use of techniques previously restricted to a small group of professionals. In particular, the use of mixed gases—various proportions of nitrogen and oxygen, or nitrogen-oxygen-helium "trimix"—with regular amateur diving equipment has considerably extended the time a cavediver can stay underwater. In the West, cavediving groups have probed several kilometers into underwater cave systems in Florida, the Bahamas and Puerto Rico, leading to fantastic discoveries. Unfortunately, however, some divers have been killed because of a lack of proper planning and equipment, and those unnecessary deaths have given the sport a bad reputation.
I gathered a group of six divers together and we set out to Ain Hit. The cave begins with a round opening some 15 meters (50') across beneath the porous limestone that makes up the Sulaiy Escarpment. At the base of the escarpment, the cave entrance penetrates a stratum of the blue-gray, veined Hit Anhydrite Formation—an important layer of rock both for cavedivers and for the oil business in Saudi Arabia. It was laid down on top of limestone beds by the evaporation of mineral-rich ocean brines during the end of the Jurassic Period 140 million years ago.
Anhydrite, a form of calcium sulfate, is a soluble mineral when near the surface, and water has been infiltrating here for many thousands of years, dissolving deep chimneys in it. Along joints or fractures, groundwater flow has dissolved horizontal expanses of the rock, creating, in some areas, dense networks of caves, caverns and tunnels. But deep underground the anhydrite is impermeable, and much less soluble. It thus forms a cap atop the limestone that oil cannot penetrate. Without this impermeable cap of anhydrite, it is almost certain that little of the oil now found so abundantly in Saudi Arabia would still have been there in our time.
The anhydrite formation was named after Ain Hit, where the oil explorers supposedly found the first surface outcrop of anhydrite in the kingdom when King 'Abd al-'Aziz Al Saud invited them to a picnic at the Hit spring. In fact, the discovery at Dahl Hit came in 1938, after oil in commercial quantities had been found in the Eastern Province, and what was discovered was a tar seep and an outcrop of the same anhydrite cap rock that covered the main oil-bearing sedimentary formation beneath the Eastern Province. This spurred the oil explorers to extend their search of these formations, and resulted in a considerable upward revision of the possible extent of Saudi Arabia's oil deposits.
The cave system, down to water level, is divided into three separate chambers. (See next spread.) The floor of the first cave, sunlit, descends at about a 45-degree angle for some 75 meters (250'). It is not really a difficult climb, but hard enough with diving equipment on your back! The floor is covered with sharp limestone boulders: These are pieces of the roof that collapsed into the original cave, which was formed as the anhydrite dissolved out from under overlying limestone.
To reach the second chamber we had to crawl through a small opening, and the diving equipment had to be lowered on ropes from a shelf hanging out over the chamber. Here the last sunlight disappeared, and we had to turn on the lights we had brought. This chamber, about 25 by 10 meters (80 by 32') and with a ceiling 10 meters high, led through a larger, steeply sloping opening into the third and last chamber, about three times as big the second one, where we found the water.
We rigged gas lamps to illuminate the cave. In my 30 years of diving, I had never seen such clear water. That clarity, and the utter stillness of its surface, made it hard to see where the water actually began, and refraction made it look far shallower than it actually was. The bottom shimmered light green, and we could see a black hole, the entrance to an underwater cave.
We put on our diving equipment. We would dive in pairs, with one diver connected to the shore by a lifeline; the other divers, the land team, would tend the line. We brought neutral-bouyancy chemical lightsticks to leave behind us as we swam; they would mark the way back in case we lost the lifeline. Both divers carried powerful flashlights and smaller extra lights.
We had no idea what lay before us. I thought about the powerful currents I had seen in the waterholes at al-Kharj and wondered if we would encounter a similar flow here, and perhaps be swept into the unknown depths. I instructed the line tender to keep the rope taut at all times, so we could signal by tugging on it. With my heavy diving gear and photographic equipment it was tricky to walk the few steps down to the water, but soon we were in it.
We went over a ledge and down into a house-sized underwater cave. The water was so clear that our flashlights could illuminate the entire room. The floor was covered with a silt of anhydrite, as fine as flour. When stirred by the gentle currents we created, it made the water as white and opaque as milk. We had to be very careful not to ruin our visibility.
Down in the silt I could see the glitter of beautiful gypsum crystals large enough to hang on a chandelier. We left lightsticks in our wake as we swam on to where the cave forked into two passages. One, straight ahead, narrowed into a black tunnel; the other, below, fell away in a narrowing canyon. We could see a black hole where it disappeared from sight. Fortunately, we could not detect any current.
We decided to explore the forward route first. My partner led with the lifeline while I followed, keeping one hand on the rope. The shapes of the walls were surreal, seamed with shelves of anhydrite and limestone strata that were covered with white silt, as if it had been snowing. Where our exhalation bubbles struck the roof, flakes of loose rock came down like fatter snowflakes, but they did not affect our visibility. The silt was a different matter, though. We had to move very carefully, gliding through the water with almost no movement. The tunnel narrowed more and more. Finally, after swimming about 150 meters (500'), we came to a dead end and turned back. The line tender was doing his job well, and we had no problem following the rope as we retreated.
Since the straight-ahead route was blocked, we decided to see if the descending canyon would lead us further. We swam down in a zigzag course that avoided the silt-covered shelves. We saw several side tunnels, but stuck to the main shaft as it became narrower and narrower, finally stopping at an opening only big enough to let one person through. I looked at my depth-gauge—it showed 17 meters (55')—then glanced back the way we had come.
What I saw made me uneasy: The lifeline had snagged on the rock in several places. That meant that we no longer had signal contact with the land team. And a cloud of white silt that we had kicked up now came rolling down toward us like a fog. If we lost visibility, our situation could become quite dangerous.
It did. Before I could signal my partner to turn back, he started to wriggle through the tiny opening, kicking violently. In an instant all visibility was gone, and we were groping in a milky soup. Weightless in the water, we had no way of judging direction. Only the rope leading upward offered a chance of returning safely—and we could see less than an arm's length of that, a whiter white in the flashlight's beam. Desperately signaling, I began a slow ascent, following the rope hand over hand. I saw the gleam of my partner's torch, and knew that he was following.
Fear, more dangerous than the loss of visibility, started to slow my thinking. I knew I had plenty of air left in my tanks, but I felt I was not getting enough with each breath, and I began to breathe heavily. I had to regain control of myself before I did something irrational and potentially fatal, like leaving the lifeline for an uncontrolled ascent. Without letting go of the rope, I sat down on the floor of the tunnel and concentrated on calming down.
Then I went on, hand over hand along the rope, until I came to the first point where it had snagged. I needed both hands to free it, and I had to put the light aside. In total darkness I loosened the rope by touch and went on. After several similar stops, the rope was finally free, we were back in touch with the line tender, and my feeling of security returned. Soon we found the lightsticks that we had left to mark the tunnel entrance.
When we climbed out of the water, we found that our land team had been very worried ever since losing contact with us. We were all shaken by the danger we had been in. After an exhausting climb back up to the main entrance, I was glad to see the sun again.
But my partner told me that, before we had turned back, he had peered through the hole he was trying to squeeze through and had seen the tunnel continue at least as far as the light beam reached. That hole presented an irresistible challenge to find out what was on the other side—but I had learned that we required better safety precautions. To push onward in this cave, I needed more expertise, as well as backup equipment. I was taking my first steps into serious cave diving.
It was a stroke of luck that I got a telephone call just a few weeks later that made those steps possible. The caller was Mike Gibson, an experienced cavediver who had explored the famous caves in Florida and Puerto Rico. He had just arrived in Saudi Arabia, and, on the remote chance there would be cavediving opportunities in the kingdom, he had brought all his advanced equipment. Mike was delighted to find a fellow cavediver, and I found his experience gave my confidence a big boost. Together we planned further exploration of Ain Hit.
I went back to the cave two months later with Mike and with Arlene Foss, an experienced diver who had been with me on my shark expeditions. (See Aramco World , March/April 1996.) Mike went down first, alone, to secure a permanent lead rope through the small passage where we had turned back. The cavediver's rule is to use one third of the available air swimming in and one third coming back, and to keep the last third in reserve; Mike planned to follow that rule, but he carried two independent breathing systems with a regulator on each tank. He had a hand-carried halogen light, two additional lights fixed to his helmet and two reels of rope, one of which would serve as the main-shaft guideline and the other to explore detours from the main passage.
Mike came back less than an hour later with an exciting report: There was indeed a continuation, and it looked big! But Arlene's and my exploration would have to wait until the following week, to allow the silt to settle and visibility to return.
The next week, Arlene led as we went down. We headed straight for the entrance to the second underwater chamber. Mike had done an excellent job with the rope, securing it to rocks so it passed half a meter or so (1½) above the silt. Even so, Arlene could not avoid stirring up a white cloud in the narrowest part of the four-meter-long (13') tunnel, so I had to pass through blind. Carefully, I pulled myself through, my tanks scraping the roof.
When I emerged, my light revealed a magnificent dome-shaped cave 10 meters (32') high. The water was flawlessly transparent and our light spread through the whole cave, which measured about 25 by 10 meters (80 by 32'). Arlene was hovering under the ceiling, as one might float weightless in a dream. The white silt layer gave the floor soft, rounded contours, whereas the walls and roof had shelves with sharp edges. There were no stalactites or stalagmites to indicate that this cave had once been dry. When I looked into a small hole in the wall, it was filled with the most beautiful small gypsum crystals, not unlike what might be found in an ice cave. We came to call this chamber "the Dome."
From our entrance hole the slope went on, and I could see another tunnel opening at the far side of the room. Near it I spotted tiny tracks in the silt, like the insect tracks you see in desert sand—evidence that there had been life in this eternally dark place! Like the footprint of an astronaut on the moon, however, the tracks might have been made long ago; it was impossible to guess how quickly the cave's slow silt-fall would finally cover them. But in fact I soon found the maker of the tracks alive: a tiny, transparent, shrimp-like crustacean called an amphipod. Our lights made his red hemoglobin visible through his transparent shell.
So far, this species does not fit any of the descriptions we have found, and considering the awful isolation of the place, it may well have evolved here and remained unknown to science. As there is no light in the caves, it is presumably blind. There is a minimal current in the water, and perhaps that flow carries in nutrients from areas exposed to sunlight. Or maybe these creatures are at the top of a food chain which starts with bacteria that draw energy not from sunlight but from chemicals such as sulfur and hydrogen, like the bacteria that are the base of the midocean hot-vent ecosystems.
I continued down the slope, following Arlene and the rope, and went through the next opening at a depth of 26 meters (85'). After a 90-degree bend and a smaller chamber with a choice of exits, we came upon yet another "cavescape."
The roof was lower here, but the cave extended horizontally in all directions, shaped like a big bubble in the limestone. This chamber was therefore probably not the work of running water, but had been formed instead by slow dissolution of the rock. It looked like the prayer hall of a mosque, with pillars and arches. Here the rope ended, but I explored around the perimeter of the chamber and found a narrow tunnel leading to the right. It was tempting to continue, but we were far inside the cave system, under 30 meters (100') of water. It was just too risky to penetrate this very narrow tunnel, at this depth, without a guide rope. We started our return.
On my way back I suddenly heard an eerie rumbling, echoing sound that made my blood freeze: It sounded like falling rocks. For a moment I expected the ceiling to collapse. I looked upward, and saw that the roof of the chamber was dotted with bubbles of our exhaled air that had filled small pits and irregularities in the rock surface. When we swam through the chamber on our return, the added bubbles started to run along the roof to higher points, and it was the movement of the bubbles that was making this otherworldly sound.
We continue to explore the Ain Hit cave system. After our first five trips, I set up a "permanent" camp at the site, so all we had to carry in was tanks of air. Nonetheless, it remains a difficult, lengthy task, since we can dive only once at each visit, because of the silt. To climb down to the water and, hours later, back up again, carrying a full load of diving gear, in temperatures that sometimes reach 45 degrees (113°F), is a real test of our endurance and enthusiasm, but both have yet to flag.
People often ask me about the fear that must accompany diving in narrow tunnels, in total darkness, in deep water, where there is no sunlit surface—and no air!—overhead. I usually answer that it is healthy to be a little bit afraid in such a place: I find that fear, kept in check, sharpens my instinct for self-preservation. People also ask why I like to dive in a black hole where there are no colorful fish or beautiful corals to see. The answer is, curiosity: to find out what is around the corner. When I pass through the small entrance of the inner cave at Dahl Hit, it is like stepping down from a spacecraft onto the moon. I hover in weightlessness in a surreal, silent place, a landscape that reveals shapes and spaces and colors to my lights, a place where nobody has been before. This delight is always coupled with anxiety about what could happen, but the sirens of the desert caves are singing their song to draw us in, ever farther.
Erik Bjurström, a consultant at tht King Faisal Specialist Hospital and Research Center in Riyadh, has lived in Saudi Arabia for 13 years, and has made more than 40 dives into Ain Hit so far. He extends special thanks to all his dive buddies and "sherpas" whi made this article possible especially Arlene Foss, Mike Gibson, and Alex at Sea and Sun dive shop in Riyadh.