1. Do people feel lighter when floating in the Dead Sea?
Photos of the Dead Sea often show people lying on the water reading newspapers or books. Japanese encyclopedias describe it as a lake where you can float and read. [7] Looking at these photos, it might seem like your body becomes lighter when you enter the water. However, your weight does not change just because you move to a different place. What changes is the density, or heaviness, of the water around you.
To understand this, let us first look at what happens to people in a normal ocean.
2. Do people float or sink in normal ocean water?
Materials for teaching swimming in clothes state that the specific gravity of the human body is about 0.98 when inhaling and about 1.03 when exhaling. [3] Specific gravity is the ratio of weight compared to the same volume of water. If the number is less than 1, the object floats; if it is greater than 1, it sinks. This means you float when you breathe in and sink when you breathe out.
What decides whether you float or sink is buoyancy. According to Archimedes’ principle, when you put your body in a liquid, you are pushed up by a force equal to the weight of the liquid you push aside. [4] If your body weighs less than the water you push aside, you float. Since a body with full lungs weighs almost the same as water, you float in the ocean with most of your body still under the surface.
There is a famous story about Archimedes discovering this principle while bathing and solving a mystery about a crown. However, this story is separate from the actual discovery of the principle. The first book to mention this story was written about 200 years after Archimedes, and its reliability is questioned. [4]
3. How much heavier is Dead Sea water than ocean water because of salt?
Dead Sea water contains a lot of dissolved salt. Ocean water contains about 35 g of salt per 1 kg, while Dead Sea water is measured to contain about 340 g of salt per 1 L. [8][1][2] This is nearly 10 times the concentration of ocean water. However, the salt content in the Dead Sea varies depending on the source, location, year, and definition.
Looking at density, ocean water is about 1.023 to 1.028 g/cm³. [9] The raw water of the Dead Sea, as measured in a paper, is 1.241 kg/L, or about 1.24 g/cm³. [2] For the same 1 L volume, ocean water weighs about 1.025 kg, while Dead Sea water weighs about 1.24 kg. This means Dead Sea water is about 20% heavier.
If you put these waters in a 1.5 L bottle, there is a difference of about 300 g between ocean water and Dead Sea water. Note that the chemical components of the salt in the Dead Sea are different from normal ocean salt. Therefore, density might not be determined by salt percentage alone. For now, we only use the fact that a lot of salt makes the water heavy.
4. How much of a floating person's body stays above the water?
When floating, the percentage of your body volume that is underwater can be calculated by dividing your body density by the water density. This is based on the idea that you float where the weight of the pushed water balances your body weight.
If you take a deep breath (body density 0.98) and float in ocean water (about 1.025), the calculation is 0.98 ÷ 1.025, which is about 0.96. This means about 96% of your body is underwater, and only about 4% is above the surface. In Dead Sea water (1.24), the calculation is 0.98 ÷ 1.24, which is about 0.79. This means about 79% of your body is underwater, and about 21% is above the surface.
The part of your body above the water increases from about 4% in the ocean to about 21% in the Dead Sea. This is roughly a 5 times increase. The feeling that your body sticks out higher in the water comes from this difference.
If you exhale (body density 1.03), you would sink in ocean water (about 1.025). However, in Dead Sea water, 1.03 ÷ 1.24 is about 0.83. This means about 83% of your body is underwater, so you still float. These are theoretical estimates based on density ratios, not measured values. Your actual floating position changes depending on the position of your head and lungs, and your body shape.
Do this experiment with an adult.
5. Why did so much salt build up in the Dead Sea?
The Jordan River flows into the Dead Sea, but no river flows out. [5] This means water is lost mainly through evaporation, though some is used for mineral extraction. When water evaporates, the dissolved salt does not evaporate and stays in the lake. [5]
The water that enters evaporates and leaves, but the salt remains. This cycle has continued for a long time, making the water very concentrated with salt. The geography of being a lake with no outlet is the background for why the water became so salty.
Because the salt concentration is so high, there are almost no fish or larger creatures in the lake water. Only very small microorganisms like bacteria have been found. [1] The name "Dead Sea" comes from these features.
6. What is happening to the Dead Sea's water level now?
The surface of the Dead Sea is about 430 m lower than sea level, making it the lowest place on land. [7] The elevation changes from year to year, and values vary by source, so dates are included. In 2019, it was −433 m. [7]
In recent years, the water level has dropped by an average of about 1 m per year. [6] The area of the lake has also shrunk from about 1000 km² in the 1960s to about 605 km² in 2016. [7]
There are two main reasons for this. First, water from the Jordan River has been used for irrigation (watering crops) since the 1960s, reducing the flow into the lake. Second, minerals like potassium are extracted from the lake water. Geologists estimate that mineral extraction causes about 30% of the water level drop. [6][5]
On the lake shores where the water has receded, sinkholes have formed. Since the 1980s, it is reported that up to about 5,000 sinkholes have formed. [6] These are caused by fresh water seeping into underground salt layers and causing them to collapse. The lake where you can float and read a book is still changing shape today.
7. How can you test floating with salt water and an egg at home?
If you want to investigate further, you can try this at home: Dissolve salt little by little into a glass of water and put a raw egg in it. Watch whether it floats or sinks, and see how it changes as you add more salt. Do this with an adult.
This is not an experiment to recreate Dead Sea water exactly. It is just to see one point: "Heavier water makes objects easier to float." Writing down how much salt you added will help you compare the results.
If you want to research more, look at a map to compare the location of the Dead Sea, the Jordan River, and the areas where the water level is dropping. This helps you imagine the shape of a lake with no outlet.