Initially, bodies will likely sink to the bottom, but as bodies decompose and gasses are released in the body, the corpse will rise back to the surface as a result of buoyancy.
Imagine that you’re going for a swim down at your local watering hole. The summer sun is shining and the weather is perfect for a dip in the lake. However, when you arrive, to your absolute horror, you find a dead body floating in the middle of the water.
As terrible as this series of events would be, it does raise some interesting questions. First of all, when human beings try to float in water, it takes a bit of effort, or concentration, but that doesn’t seem to be the case with dead bodies. Whether you spy a corpse in your nearby lake or your favorite TV detectives find a body in the bay, it always seems to be floating… but why? Why do dead bodies seem to naturally float?
Dead in the Water
When a body is found floating in a body of water, it doesn’t immediately mean that they drowned. Just think about all those mobster movies when they dump bodies into rivers and shipping lanes. In fact, if a person drowns, it will probably take even longer for the body to return to the surface of the water. See, when a dead body first enters the water, it does sink to the bottom. Water will eventually fill up the lungs, expel any excess air, and bring the corpse to the bottom.
The reason that living human beings naturally float is because of the air in our lungs. The air acts as a buoyant force for the body, making it impossible for you to simply lie down at the bottom of a swimming pool. In the case of a corpse, however, they have no control over whether their lungs fill up or not. If the corpse falls in the water facedown, they might never sink to the bottom, as there will be no real chance for the air to escape from the lungs. However, if a corpse is put into the water on their back, air can escape, water can take its place, and the body will quickly sink.
If a person drowns, they don’t necessarily die because water fills up their lungs; often, the body will asphyxiate itself because the windpipe closes up against the presence of water. In this case, a body could potentially float for longer periods before eventually sinking to the bottom. However, given that almost every dead body falls beneath the surface eventually, once all the air is expelled from the lungs, why do they always seem to be “popping up”?
Back From the Depths
When someone dies, their body is unable to maintain a stable environment, and the immune system is obviously not helping any longer. Thus begins the long process of decomposition, in which bacteria both inside and outside the body begin to break down the integrity of the body’s cells. This body is also known as putrefaction, which is the series of physical, chemical and biological processes that will eventually fulfill the whole “ashes to ashes, dust to dust” destiny of the human body.
Just because the body dies, however, that doesn’t mean that the bacteria inside the body have also perished. All they need is a food source, and can even operate anaerobically in the absence of oxygen. The sugar and protein found in the body’s gut, soft tissues, muscles and other decomposable areas will be consumed gradually by this bacteria, but there is an output to this process – gas. Ammonia, hydrogen, methane and carbon dioxide are all released by these bacteria as they slowly break down a body. This gas has nowhere to go, however, and will begin to fill up other parts of the body.
As the body slowly begins to swell and rot, that newly formed gas develops the same penchant for buoyancy as oxygen, which eventually raises the corpse back to the surface of your favorite swimming hole. The volume of the body will notably increase, but the person’s weight will not, thus making it easier for the body to float. After initially sinking, the body will return to the surface within a few hours, or it could take days – even weeks!
When the corpse does come back up, packed with gas and often bloated beyond recognition, the fresh gas buildup can be relieved. The corpse may rupture because of the air pressure inside, or the gas will simply escape in a more normal way. At this point, the body may sink for a second time, only to have the decomposition and putrefaction process to continue, filling the body with gas and eventually sending it up – a (somewhat) endless cycle.
To press this morbid subject a bit further; most dead bodies are seen floating face-down, and there is actually a good reason for that. Since the gut and chest cavity have the most bacteria, the most bloating will occur there, and any float back to the surface will be led by these buoyant areas of the body. Based on human anatomy, the limbs and head tend to fall/bend forward, rather than backward, so dead bodies in water seem to naturally orient themselves in the face-down position, in the majority of cases, unless you’re an otter, of course.
While decomposition is almost inevitable for anyone who dies, the process occurs even slower underwater, and is particularly sluggish at extremely cold temperatures. This means it would take longer for the gas to re-fill the cavities and raise the body to the surface. So, if you are ever in the unfortunate position of having to dispose of a body, and you don’t want it popping back up within a few days (or even sooner), be sure that the water body is as cold as possible – and maybe even add some “cement shoes” for good measure!