SINKHOLES MAKE FLORIDIANS NERVOUS

OBSERVATIONS FROM NORTHERN FLORIDA
On March 1, 2013, the tragic story of Jeff Bush, a 37 year old local man who was tragically swallowed up in a sinkhole, near Brandon, in Hillsborough County, near Tampa Florida, hit the press. Since then, similar fearful stories have abounded here in northern Florida and across the nation. Sinkholes, the collapse of overlying rock and debris into unknown and virtually unpredictable subterranean voids caused by chemical solution of basement rock, are surprisingly very common, here in Florida and around the world wherever limestone beds occur below the surface. Some stories are more bizarre and frightening than others, and some, like the process itself, go back to into ancient times.

One of the most bizarre stories of sinkholes and human reaction to them, was recorded early in the First Century by the Roman historian Livy. Titus Livus Patavinus, (Livy) 58 BC to 17AD was a Roman historian whose masterwork was a history of Rome, entitled, "Ad Urba Condita”, (or “From the Founding of the City”). Livy lived during the period of the Roman Republic into the reign of Augustus. In the early books of "Ad Urba Condita", Livy tells of a “chasm” that opened up in center of the Roman Forum in 362BC. The feature seems to have characteristics of what we would call today a sinkhole. (However, since there is no limestone or significant other carbonate rocks in the Forum region, the chasm was NOT a true sinkhole). Livy's historic aim was to teach moral lessons to his Roman readers, and often padded his stories to that aim, so he may have transposed the elements of one story into another in the process changing the venue of the story to that of the Roman Forum.

According to Livy, the "chasm" formed in the very center of the Roman Forum, the heart of Rome's religious and commercial center. The depression continued to collapse and grow, quickly widening so as to threaten the foundations of a cluster of sacred and commercial buildings nearby. The citizenry were understandably terrified. Based on the minimal knowledge of the physical world at that time, they could only conclude that the gods were angry with Rome (perhaps due to the recent wars of aggression it had waged) and with its citizenry and must be propitiated with votive offerings. To please the angry deities, the people tossed various belongings into the hole, jewels, gold, brass trinkets, and they made animal sacrifices at the near-by Temple of Vesta. Their offerings and prayers were to no avail, the hole continued to grow wider and deeper. The frightened populace sought out augurs or priestly soothsayers to interpret the will of the angry gods. The augurs, who each carried a short wooden wand curved at its end into a spiral, and used these wands like divining rods as they studied the flight of flocks of birds, or the twists and turns of the the entrails of a sacrificed animal to make their predictions and pronouncements. Shortly, the priests announced the results of their divinations, stating,”the gods will be satisfied with only ’the most precious thing of all’". The citizenry puzzled over the statement. Entreaties went out to the city's wealthy elites, for more meaningful and worthy sacrifices and more valuable goods to satisfy the tastes of the Roman pantheon. Some of these wealthy worthies gathered their families then slunk off to their retreats in Campania, or Naples, to get away from the City and the angry gods, while others less willing to retreat, reluctantly gave up new offerings which they claimed to be “the most valuable of all". But nothing stopped the sinkhole from widening and collapsing, as earth continued to slip down into a large void beneath the heart of the City.

It was at that point that a young equite, Marcus Curtius, came forward with is own interpretation of the augurs’ divinations. Marcus was a member of the privileged class who went into battle mounted on a horse (hence the term "equite") and bore the name of a famous and ancient Sabine family. The Curtius family (or gens) was one of the founding one-hundred families of Rome. Young Marcus reasoned that the augur's statement, "the most precious thing of all" was clearly the strength and courage Rome's soldiers, who defended the City from its enemies and were responsible for its very existence. “We would not be here were it not for our courageous fighting men”, explained Marcus. “They are the most valuable of all.” The very next day, the young man dressed himself and his mount in their finest military equipment, preparing himself and his favorite stallion as a human and equine sacrifice for his native City. Then, with the morning sun reflecting brightly off his polished brass cuirass, his greaves and plumed helmet, he urged his horse into a galloped his down the center of the Sacred Way of the Forum. Reaching the edge of the sinkhole, he pulled back on his beautiful steed’s mane, and drove his heels hard into its soft flanks as they both leaped into the great sinkhole. Horse and rider disappeared almost instantly. As Marcus’ plumed helmet disappeared below the shifting, pale-yellow sand, the walls of the sinkhole stopped collapsing and the earth stopped moving.

The amazed citizenry rushed to the very edge of the depression and stared down into the vacant, now stable abyss. Nothing stirred at the bottom. There was no sign or sound of Marcus or his horse. The bottom remained stable. But slowly, during that first day water percolated up from far below to soak the loose bottom sand. In time, the depression slowly filled with water to form a lake, eventually known as Lacus Curtius, named after the young man who sacrificed himself and his horse for his City. Later, as is a normal part of the natural progression of lakes, the lake edges became lined by sedges and marsh grasses which slowly grew toward the center as the lake evolved into a marsh. That part of the Forum remained as a low marshy area with a pool of fresh water in the very center until near recent times. Note that there are several other myths and ancient accounts regarding how Marcus Curtius died, this is one of them.

The history of Rome and Livy's recounting of Marcus Curtius' sacrifice and the Roman Forum is little known here. But when "In The News” (ITN) reported the events surrounding Jeff Bush's tragic death on March 1, many in Florida listened listened attentively. ITN recounted how Jeff's older brother, who lived in the same house, was awakened around 11 PM by anguished screams coming from his brother's bedroom. When the elder Bush reached his brother's bedroom door, he found it ajar. Inside he was shocked to find nothing there, no floor, no furniture, no bed, only a deep churning earth-filled hole in the center of the room. In the dim light, he recounted how he could see his brother, entangled in bed-linens and mattress as he was being dragged downward, with other room debris, sucked into a dark, growling, sandy abyss. Bush tried to reach his sibling, but the sand gave way under his feet as the sinkhole widened. When emergency services arrived, they were able to extract the elder Bush from a portion of flooring on the edge of the still growing hole, but Jeff Bush was no longer visible. Emergency crews working from outside the building cautiously dropped cables with listening devices into the widening hole in an attempt to hear the buried man, and ascertain if he was still alive, but the only sounds they detected was the grinding of rocks and debris and the flow and swirl of moving sand, as the sinkhole continued to enlarge and deepen. Very quickly the depression widened to encompass an area 100 feet wide, threatening to swallow up the entire Bush house and possibly neighboring homes as well. Jeff Bush was not heard from again and is presumed dead. (See “In The News” http://inthenews.biz/2013/03/01/florida-man-Jeff-bush-trapped-inside-sinkhole-is-presumed-dead/).

Sinkholes are collapse structures common in areas underlain by limestone rock. About 20% of the nation has basement rock of this variety. Limestone is formed mostly as a result of biochemical processes under sea water and is composed of calcium carbonate. Limestones react with slightly acidic groundwater to produce calcium salts and carbon dioxide. When this reaction occurs it alters the solid crystalline rock into a tiny pinch of soluble salt and a belch of carbon dioxide gas, thus creating an empty space where solid rock had formerly existed. Naturally acidic rainwater (its acidity is the result of falling through air laced with carbon dioxide), seeps through the porous overlying rock to dissolve limestone and to eventually produce large voids or empty spaces in the formerly solid rock. These are known as “dissolution” cavities. Over long periods of time, these voids expand and coalesce into larger spaces which may further enlarge into caves and eventually into massive caverns such as those of world-famous Carlsbad Caverns in News Mexico, and other similar caverns found world wide. The final phase of the solution processes, when much of the underlying limestone has been dissolved away, leaves an irregular pock marked form of topography with isolated hills and elongated valleys known as "karst topography". Karst topography is found over wide areas of southern, central and western Florida, and many other states in the nation. In Florida, many large urban developments have been built directly over these areas, and so we can expect to continue to hear more of sinkholes swallowing cars, people and houses in the future.

If the limestone beds with their caves and caverns are close enough to the surface, as in most of Florida, where typically, the limestone bedrock is covered with between sixty to one hundred feet of friable rock or loose sand and shelly gravel, sinkholes can and do form at the surface. This collapse process occurs when, for one or more reasons, the roof of the subterranean cave, cavern or empty space underground can no longer support the overlying rock and it collapses down into the subsurface carrying down with it the overlying sand and gravel--and any man-made structures perched on it or located nearby. The presence of these deep, hidden,underground features which can lie undetected beneath a seemingly solid, placid, earth surface which without notice or warning can collapse bringing down with it man made structures which we imagine to be solid and unmoving in a wink of an eye. Thus the formation of sinkholes remain mysterious, unpredictable and frightening events.

Almost every state has some areas of this rock type and so the encounters described above are more common than most of us suspect, in part as a result of the fact that more and more of the nation's land is occupied by housing, parking lots, roadways, factories, shops, etc., making the likelihood of humans or their structures being affected by a subsurface collapse or sinkholes more and more likely. Furthermore, long term droughts, something we have been suffering from here in Florida, and the heavy pumping of groundwater reserves, or the “mining” of groundwater ( i. e. for “spring water”) for commercial bottling plants for example, and for other purposes can lower ground water tables and exacerbate the collapse process by reducing internal water pressure in the rock structures underground. It is also possible that increased groundwater acidity, and other human activities may also be part of the cause.

Get the picture?
rjk