More than 60 million years ago, a vast sea rolled where today Saudi Arabia's central deserts lie. In that sea, with each cycle of birth and death, the shells and bones of countless creatures slowly sank to the ocean floor. Over eons they solidified into limestone and dolomite, beds of rock which today make up the Arabian Peninsula's Umm er Radhuma formation, which stretches from Iraq and eastern Syria south to Oman. In those truly ancient times, the Peninsula was separating from Africa, moving eastward, pivoting counter-clockwise around a point somewhere between Amman and Beirut. The Great Rift Valley was forming all the way from Jordan to Mozambique, bringing the Red Sea into being, and the Peninsula as a whole developed a tilt toward the northeast.
Through subsequent epochs, there were both wet times and dry times. In the pluvial periods, rain would sometimes pick up enough carbon dioxide from the atmosphere to become slightly acidic. When runoff flowed into the cracks in the limestone and dolomite, this "acid rain" slowly ate away at the rock, leaving patches of eroded limestone called karst. Over time, cavities formed, and still more runoff from the surface filled them. Eventually, some of these cavities contained underground lakes and rivers. In the alternating dry periods—such as the one that began in the Peninsula some 18,000 years ago—only a little water percolated down, and the underground water levels slowly dropped, allowing some caverns to fill with air. In them, one mineral-laden drop at a time, stalactites and stalagmites formed. Today, some of those formations have been dated to more than 270,000 years ago, while others are geological youngsters only about 11,000 years old.
To the people of Saudi Arabia, the Umm er Radhuma region has been known for its water-holes. The vast body of rock, one of the seven major geological formations that make up the eastern portion of the Arabian Peninsula, holds water that percolated into it during the last pluvial period, some 18,000 to 30,000 years ago. Further to the east, thanks to the Peninsula's northeastward tilt, this fossil water actually gushes to the surface as springs, where it sustains a number of modern agricultural projects.
As a cave explorer, I was intrigued by this gradually falling water table in a karst region: Might some of the numerous sinkholes in the area (dahl in Arabic, plural duhul) lead to limestone caverns, perhaps even caverns of great size or beauty? In the early 1980's, I began my search in an area of about 500 square kilometers (200 sq mi) around Ma'aqala, a small town several hours' drive north of Riyadh. Here, the Umm er Radhuma limestone is especially well-exposed, and dotted with hundreds of natural vertical dahls— evidence of substantial karstification and, hence, caves. Biologist David Peters, my wife Susana and I spent eight days camped atop the hardpan, guided by a Ma'aqala old-timer named Sultan.
The initial results were discouraging. In the first holes we climbed down, we found the few horizontal passages filled with fine red sand, which had either blown or washed in. But one day I chanced on a small hole no wider than a dinner plate. As I leaned over it, to my surprise, my face was suddenly bathed in a rush of warm air so humid that it fogged my glasses. Its strength suggested extensive chambers, and we were soon busy chipping away at the rather soft, marly limestone about that unassuming little dahl until it looked as though we could fit through.
We did, but just barely. After squeezing through one shoulder at a time, and feeling about for the unseen rungs of our free-swinging cable ladder, we found ourselves in a bell-shaped room about nine meters (30') deep. To our delight, the floor was covered with only a little sand—perhaps thanks to the diminutive opening above. On one side of the room, a jumble of large rocks had long ago fallen from the ceiling. Through these, we felt the current of air, and so, on our bellies, we wriggled through an opening down into a low tunnel that branched off in two directions. As we cautiously made our way into chamber after chamber, we came upon majestic displays of stalactites and stalagmites, as well as a microcosm of tiny, sparkling mineral formations: delicate gypsum "flowers" and eccentric calcite helictites that twisted and turned in all directions in apparent defiance of gravity. We named the series of rooms Dahl Sultan, after our guide. It appeared to go on yet further, perhaps for kilometers, with no sign of a second entrance. Clearly, the Ma'aqala karst promised wonderful surprises: There were discoveries to be made beneath the surface of Saudi Arabia.
We returned frequently on weekends, and Bedouins and villagers who came to see what we were doing nearly always asked if we'd found any water. At Dahl Sultan and other holes in the area, our answer was always negative, but it was apparent that there had been water there in the past: Some caves had deep grooves in the entrance lip worn by bucket-hauling ropes, which indicated that the cave had dried out relatively recently. Further evidence of past water was the horizontal bands of color on the walls of some caves, left by the interaction of water and air.
Bedouins of the region often told us of their belief that the dahls were home to jinn, spirits best left alone by humans. I was reminded of this belief when I squeezed down into one very tight hole 13 kilometers (8 mi) from Dahl Sultan. I was halfway down the cable ladder, swinging to and fro inside a large, almost round room, when I heard what sounded like a distant moan. I traced the disconcerting sound, crawling through a small opening on my hands and knees into a long, low tunnel with smooth, almost white, walls and a floor of soft red sand. The farther I made my way into it, the louder that strange wailing grew and the more beautiful the passage became, until it seemed that every bit of the ceiling was covered with delicate helictites of an ivory hue. It somehow looked like an upside-down stage crowded with hundreds of beautiful but unsynchronized ballerinas. In the last room was a sort of alcove, and in the wall above it a small hole about eight centimeters (3") in diameter through which air was blowing furiously—a natural whistle. (Later, we learned it only whistled when the pressure difference between the inside and outside air was sufficiently great.)
I poked my smallest flashlight through the hole and looked over it into a bizarrely decorated room that we now call "the closet of the jinn." It appeared that the cave continued, but there was no passage to the other side of the wall. I returned to the entrance room to report my find to my fellow cavers, but at the top of the cable ladder, I ran into a problem that constitutes one of the many hazards of caving. The ceiling of this room was nearly two meters (6') thick, and once I was inside the tight tube leading up through the ceiling, I was no longer able to raise my knee to take another step up the ladder. Try as I might, I couldn't advance! Fortunately, my plight was noticed by two Bedouin men who had been watching our day's expedition out of a mixture of curiosity and—now well-founded—concern. They reached down, grabbed the one arm that was above my head and pulled me out like a cork from a bottle.
Eventually, we managed to tunnel through the soft sand under the wall of the "closet of the jinn" to gain entrance, but we could go no farther. The strong airflow entering this last chamber was coming out of an opening too small for even a child to enter, and we could only dream of the wonderful passages that might lie beyond.
Because the Umm er Radhuma formation is tilted towards the east, its western edge appears on the surface as an escarpment running north and south along a line some 30 kilometers (19 mi) from the town of al-Majma'ah in central Saudi Arabia. One day I heard from a geologist that he had seen an unusually large and deep hole in this area, one that local people had told him might lead to an underground river that ran eastward some 300 kilometers (185 mi) all the way to Hofuf. Led by one of my English-language students, Abdulaziz Al-Agili, we packed for al-Majma'ah, where we were received by several town officials who said no one had ever found the bottom of their mysterious hole. Hospitably, they asked how we were fixed for provisions. We showed them our food box and our camp stove, which they insisted was inadequate, and they hastily assembled a too-generous package of meat, tomatoes and onions, along with a rectangular barbecue grill and several bags of charcoal. Luckily, it all fit atop our Land-Rover.
When we got there, the pit was impressive indeed. Leaning over the rampart that surrounded it, we could see a crater-like floor, in' the middle of which was a nearly square hole that looked more menacing than inviting. We hitched a rope to our truck and made our way down to the edge. We lowered our longest rope—100 meters (328')—and I tried to see if it reached the sunlit bottom, but it was so far below that I couldn't make it out. Hoping for the best, I leaned back over the maw, attached only by my rack, a descending device that feeds the rope around six aluminum bars to provide just the right amount of friction required for the free rappel.
I slowly slid down into the shaft, which was about 12 meters (39') wide, still unable to see the bottom. After a short distance, the four walls around me opened out, and the hole I had dropped through became a tiny skylight at the top of a huge, single chamber with a rounded, dome-like ceiling. I guessed it was some 100 meters (328') across and the same distance high—the biggest cave room I had ever entered. I felt very small, and I still couldn't see the floor.
My rope reached to the bottom with scarcely a meter to spare. I landed at the crest of a great heap of dirt in the center of the room. All around me, rock doves soared in and out of the sunbeam down which I had seemingly descended. I could see their countless nests resting on what looked like shelves running all around the curved walls. I soon realized that each of these ledges was actually the top of a layer of earth that sooner or later would separate from the wall.
Amazingly, there was no sign of limestone, nor rock of any kind. It was like being in the hollow center of an onion made up of layer after layer of earth. I wondered what was holding up the roof. I felt none of the confidence one has when surrounded by the solid walls of a limestone cave.
I disconnected the rope and stared at the hole I had just come through, almost hypnotized by its tiny luminosity and the sound of the fluttering, chattering doves. Then I remembered how easily I could be hit by a stone falling from the surface, and I moved toward the wall, looking for side passages. I found none, but as I walked I did frighten numerous doves that had confidently built nests directly on the ground. At one end of the nearly circular room, I found mud, but there appeared to be no drain—nor any sign of an underground river to Hofuf.
Suddenly, I heard a tiny peep far above me. My companion, Ron Kummerfeldt, a survival instructor from Kenya, had just begun his descent. Seeing him dangling there brought home the true dimensions of the cave. His rope looked like a silk strand, and Ron a spider dropping through a trapdoor in a dome bigger than any in a mosque or cathedral. I watched in awe.
Together we did little better than I had alone at finding any following passages. We did find bits of hedgehog remains, suggesting that owls might nest here, and the remains of a snake about as long as my arm, perfectly preserved right down to its teeth.
In the center of the room was just about enough debris to plug the hole in the roof, a reminder that another layer of earth could detach itself from the ceiling at any moment and end our exploration abruptly. The climb out was long and hot, and we each felt a surge of joy to be standing under the sky once more.
It was only after the climb that Al-Agili told us the local name for what was really as much a pit as it was a cave: dharb al-najim, "the place of the fallen star." No one was certain where the name came from. Since that conversation, geologists have told me there's no way a meteorite could have been involved in the formation of that hole, and that, more likely, a limestone deposit was dissolved below it, deep under the earth, causing a partial collapse. But there is a sense of mystery there, and there are moments still when I wonder whether something more interesting might not lie buried beneath the hill of rubble at the bottom of that hole.
In the winter of 1986, scientists from Dhahran's King Fahd University of Petroleum and Minerals (KFUPM) and partners from the Austrian Academy of Sciences began a systematic study of the caves near Ma'aqala and the nearby community of Shawyah. Their 600-page study is a definitive scientific document, and their calculation that some 45 percent of the area's rainfall reaches the aquifer via the many dahls is of great consequence for understanding the replenishment of the Umm er Radhuma's water resources.
One of the largest and most complex caves they discovered was a three-level system given the name UPM Cave; its largest chamber is known as Dabbagh Hall, in honor of Abdallah E. Al-Dabbagh, then director of the KFUPM Research Institute. From the high ceiling of the 45-by-80-meter (150' x 250') room hang several "live"—that is, growing—stalactites. Below them, small pools of water have created the rare conditions required for the development of "cave pearls," tiny pebbles that slowly receive coating after coating of crystalline calcite until, like their nacreous marine cousins, they become almost perfectly round. No less remarkable was a nearby pool of water that might have come out of a fairy tale. The splashing of single drops falling from the ceiling had created around the pool an ever-growing wall of delicate pastel colors that shimmers with countless tiny, sparkling crystals. These delicate formations may be unique in all of Saudi Arabia, and visitors must bear in mind that one misstep could destroy them.
One of the most unusual caves the KFUPM team found was B-7, which some local residents proposed calling Dahl Shawyah. While other caves in the area are hot and humid, Shawyah's deepest chambers, some 40 meters (130') down, are cool and dry; also unlike other caves, it is accessible through a wide, walk-in entrance. And many creatures have indeed walked in: Its dry chambers have preserved a huge quantity of bones carried in by centuries of predators, some of them bearing the tooth-marks of hyenas. Carbon dating put the oldest remains—which included bones of camels, horses, gerbils and gazelles—at about 1000 years old. On a recent visit of our own to B-7, we found that the hyena's den also held at least two human skulls, as well as a carefully folded blanket made of animal skin.
Dahl Shawyah also hosts the living: In its darkest and most remote reaches lives a small colony of shy, insect-eating trident bats (Asellia tridens). Owls and a baby fox have also been spotted inside the cave, as well as sparrows, finches, hoopoe larks and rock doves. The latter are so fond of nesting underground that a sudden rising of doves in the distance usually means there's a dahl nearby. In the occasional pools of water are often tiny fairy shrimp, whose eggs have been known to hatch after a 15-year wait for water to activate them. In the twilight zone, just inside the cave's entrance, one can sometimes find monitor lizards, spiny-tailed lizards known as dhabs, and camel spiders—large, hairy Solifugids that have the largest mandibles, in proportion to their body size, of any land creature.
Since then, I have been part of several caving teams that discovered three significant new caves in the Ma'aqala karst zone, each a showcase of diverse underground beauty. Mossy Cave rewarded its first visitors only after we had wriggled through tiny spaces where fingers of rock caught at clothing, belts and straps, while high humidity left us soaked in sweat. Two of the most impressive features of this cave are an imposing set of stalactites resembling organ pipes and a sinuous stalagmite that looks like a cobra preparing to strike. Friendly Cave, as its name suggests, is not difficult to enter. It has a smooth red-sand floor and could easily be turned into a "show cave" because so many of its formations are located in one large room. Finally, Surprise Cave requires a slide through its small entrance and a squeeze past tons of broken rock to enter spacious rooms filled with large, impressive decorations, many of which are still growing. There are curious formations such as "the chandelier," whose stalactites are entirely coated with a wax-like, translucent layer of calcite that ends not in points but in flat "duck bills," many of which are set at an angle of roughly 45 degrees. More than 500 meters (1650') of this cave have now been mapped, yet much of it remains to be explored.
Sometimes, luck plays the leading role in discovery: The entrance to Mossy Cave was found when someone took a shortcut back to where he thought he had lost a flashlight. But Friendly and Surprise caves were located through the methodical efforts of Lars Bjurström, who spent many a weekend checking hole after hole on the Al-Sulb plateau northwest of Ma'aqala.
The coming of the Internet and e-mail has changed the nature of cave exploration since we descended into our first dahls. Cave explorers previously isolated from colleagues have been able to find each other and pool their knowledge. Dramatic evidence of the resulting synergy came at the end of last year when Qurian Al-Hajri, a Saudi Aramco driller, a Bedouin, discovered an enormous pit in a plain where cavers believed nothing of interest could possibly be found. But within days, news of the discovery was posted on the World Wide Web, and a digital photograph was under simultaneous scrutiny by speleologists kingdom-wide. Several of us organized an expedition to the remote spot, which happened to lie alongside the Ghawar oil field, the largest in the world.
Al-Hajri took us across 50 kilometers (31 mi) of perfectly flat, apparently featureless desert, straight to the edge of a great scar that suddenly appeared, its blackness a dramatic contrast to the shimmering white hardpan. In classic desert-navigator fashion, he accomplished this with neither a Global Positioning System receiver nor even a magnetic compass. ("They gave me a GPS receiver years ago," he explained, "but I put it away, because I need to keep a fine edge on my senses.")
The hole measured some 20 by 30 meters (65 x 100'), and it appeared to be about 60 meters (200') deep. As we began rigging for our first descent, a group of visitors appeared. They seemed delighted we had come from as far away as Jiddah to see this local curiosity, which they informed us was named Abu al-Hol. This is the name in Arabic of the Great Sphinx of Giza, and its literal meaning—"Father of Fear"—gave us pause enough to check our ropes very carefully.
Mike Gibson and I attached our longest ropes to one of the trucks and prepared a parallel rappel into the belly of Abu al-Hol. As we slowly leaned back, the taut rope began to slide through the bars of our racks, and then we were hanging free, with a dramatic view of the enormous room above which we were now suspended. Sunlight was pouring into it at this time of day, giving us an appreciation of depth unlike what I experienced in al-Majma'ah. Rock doves soared all around us as we glided down to the top a large hill of sand.
The bottom of the cave was actually about 70 meters (230') down, and the room was easily 100 meters (330') across. Much of it was filled with enormous chunks of rock that had fallen from the limestone ceiling. We began to check the perimeter wall for possible side passages and eventually discovered a narrow crack that led us to a long, tight, straight crawlway dotted with countless tiny footprints. It was a well-traveled road for some small creature. Ahead I could see that the passage opened into a large room, but the crawl-way was too tight, and we had to leave without learning what the mysterious interior chamber would look like. A future expedition, however, may be able to excavate the sand floor of the crawlway and gain access.
When we returned home, we posted pictures of the exploration of what we called Dahl Abu al-Hol on the Web. Almost as soon as they were up, reports began to reach us of similar impressive pits near Hafr al-Batin and Khamis Mushayt, areas speleologists have almost entirely ignored to date. The exploration of Saudi Arabia's underground wonders is clearly only in its infancy.
John Pint (left) is a member of the us National Speleological Society, and with his wife, Susana, has explored and written about caves in Mexico and Saudi Arabia. He lives in Jiddah, where he teaches English and operates www.saudicavcs.com.
Lars Bjurstrom has lived in Riyadh for two years, where he practices dentistry and pursues his love of wildlife photography and—more recently—caving.