The picture on the right is an example of clapotis. It comes from a book called Sea Kayak by Gordon Brown who teaches classes in Scotland where sea and surf are notoriously rough. White water and open sea kayakers are attracted to waves and love to study all their subtleties.
Clapotis is a nautical term for standing waves. It is French for lapping of water. According to English translators it is pronounced as clap-o-tee, like a long sounding “o”, as in toe. According to my Canadian French connection, it is pronouned more like clap-ah-tee, similar to the short sound of “o” as in copper. In either case, in French, the “s”, at the end of the word indicates that it is plural, meaning more than one wave, but it is silent.
Clapotis occur when waves clap together such as incoming ocean waves running into waves that have bounced off of objects such as rocky coasts or manmade seawalls. Clapotis can be explosive and sometimes roar from the rush of the water. Like the sound of the “s” on the end, sometimes they can be silent and gentle swells like those that occur between the land masses of a mainland and its barrier islands. The ocean waves are calmer but still reflect between these land masses.
As all sea faring people well know, however, silent or not, standing waves can be deceptive, destructive and even deadly. On the bottom side they scour and tear at the footers of manmade seawalls. They similarly severely undermine and damage coasts. On the top side they can toss and turn ships about like toys in a tub.
Rogue waves are a type of standing wave. They are also known as freak or killer waves because they suddenly spring up seemingly out of nowhere and significantly increase the height and strength of a wave. They often travel against prevailing winds and currents and are sometimes preceded by deep troughs that look like a hole in the ocean. Killer waves can run aground, wreck, roll and swallow unsuspecting ships, sometimes in a matter of minutes and sometimes only seconds. For centuries scientists scoffed at sailors and claimed the sailors were spinning tall tales from too much time spent isolated at sea. New evidence, however, has rocked their boat. Sailors were right, these waves do exist. As yet, we know very little about them or what stirs them up. What we do know is that fluids basically follow pressure gradients and the path of least resistance.
In physics, clapotis are considered to be transverse waves because they can rise up. In other words, they travel up and down in a two dimensional plane. Consequently, clapotis cannot occur in rigid containers, such as water pipes in homes, because rigid containers can’t expand and allow the wave to rise. Instead rigid containers cause longitudinal waves. Longitudinal waves are caused by alternating compression and expansion of fluids or air within a confined space. For example, longitudinal waves occur in muscial instruments that use pipes to make sound. In contrast to transverse waves, longitudinal waves travel in one plane.
Unlike standing waves, water hammers occur in rigid containers, such as pipes, when a forceful stream of moving water is suddenly stopped. The rapid change in velocity causes a collision similar to a standing wave but the outcome is different. Because the wave cannot increase in height it causes compression (a longitudinal movement), which increases pressure that travels back through the pipes. The stiff pipes absorb the energy, which causes them to shake along their course. Unlike the “s” at the end of clapotis, water hammers are not silent. They make a loud banging noise like someone hammering on the plumbing. Over time, water hammers can break pipe joints.
When it comes to standing waves and water hammers, the latest research is starting to connect faulty cerebrospinal fluid (CSF) flow with the cause of neurodegenerative diseases such as Alzheimer’s, Parkinson’s and multiple scleriosis, which is the subject of my book, “The Downside of Upright Posture”. I started looking into the role of CSF in neurodegenerative diseases about thirty years ago because of my background in upper cervical chiropractic and craniopathy, which led me to the subject of physical anthropology.
Upper cervical chiropractic taught me the importance of the upper cervical spine and base of the skull to human health. Craniopathy taught me about the design of the human skull and the movement of cerebrospinal fluid through the brain and cord. Because of craniopathy, I also became interested in the base and sutures of the skull. In particular, I became interested in the sutures that unite the membranous bones of the skull that form the cover over the cranial vault, which contains the brain.
The picture above on the left shows the sutures at the back and bottom of the skull. Like all bones, the sutures are a reflexion of the mechanical stresses that strained and shaped them. Early anatomists called them sutures because they thought they looked somewhat similar to surgical stitches. But to me they look more like waves and they are shaped that way for a reason. They are similar to a seismic recording of pressure fluctuations and movement in the skull and cranial vault. The pressure fluctuations come from a combination of neurological (electrical), circulatory and respiratory waves. Upright posture and bipedal walking further amplify those waves.
CSF is a watery fluid produced in cavities of the brain called ventricles. CSF flows out of the ventricles and into the cisterns and subarachnoid spaces of the brain and spinal cord. The role of CSF is to cushion, protect and support the brain to prevent it from sinking inside the cranial vault. It also carries waste out of the brain.
CSF is under constant fluctuating hydraulic pressures due to the pumping of the heart which increases arterial pressure in the brain when it contracts. Likewise, breathing causes changes in pressure inside the ribcage. During exhalation pressure inside the ribcage increases. Among other things this increases venous pressure which is transmitted to the vertebral veins. The vertebral veins are connected to the dural sinuses of the brain and like the dural sinuses, have no valves to prevent inversion (reverse) flows. Consequently, respiratory pressure changes are transmitted to the brain and exhalation increases intracranial pressure.
Because the cranial vault is a closed container, the increase in blood volume and intracranial pressure needs to be controlled. When things are working properly, any excess CSF volume and pressure is typically vented out of the cranial vault via the foramen magnum and down into the subarachnoid space of the spinal canal. Inherited (genetic) and acquired (aging and injuries) structural problems in the cervical spine can cause back pressure against the venting mechanism. If outgoing CSF waves meet resistance or inversion flows of blood and CSF waves coming up from the vertebral veins and subarachnoid space (contains CSF) in the spinal canal then clapotis (standing waves) or water hammers can occur.
In the sketch above on the right, the brain is like a landmass inside the cranial vault surrounded by a sea of CSF and venous blood in vessels with no valves to prevent inversion flows. The skull is a fairly rigid container. Consequently, the amplitude of any standing waves (clapotis) in the brain is limited. Thus the standing wave that occurs as CSF in the brain claps into CSF in the cord as it attempts to flow through the foramen magnum and out of the cranial vault becomes more like a water hammer.
In either case, the first areas of the brain to receive the brunt of either clapotis or water hammers are the basal cisterns that surround the cerebellum and brainstem. It is possible that over time, chronic clapotis (standing waves) or constant banging from water hammers in the basal cisterns weaken and eventually erode the soft tissues of the brain the same as rocky coasts.
Similarly, I suspect that standing waves and water hammers may also play a role in the formation of arachnoid cysts and empty sella syndromes, as well as the Dandy-Walker and Shy-Drager syndrome (a variant of Parkinson’s disease) type cysts seen in the ventricles and cisterns.
For a better understanding of the big picture read my book. For further information visit my website at www.upright-health.com.