The physics of scuba diving

Photograph: Lewis Mulatero/Getty Images

From Wired by Rhett Allain

A deep dive into the science of staying alive underwater.

I used to scuba dive way more than I should.
I pretty much did everything: open-water dives, technical dives, spearfishing, and cave diving.
It's a fun sport that allows you to see some incredible things, but there’s also tons of science that goes into the process of safely putting a human underwater.
So let’s discover what scuba diving can teach us about physics.

Pressure

Perhaps the first thing a scuba diver thinks of when dealing with pressure is tank pressure.
Scuba tanks contain a lot of air in a relatively small volume, and the only way to do this is to compress the air, producing high pressure.
A diver can determine the amount of air left in a tank by using a pressure gauge.
Usually, a full tank has a pressure of 3,000 pounds per square inch (psi).
If you get below 200 psi, you should be out of the water.

Normal air—the stuff that blankets the Earth—is mostly nitrogen molecules, which make up about 79 percent of it.
The rest is oxygen, at around 21 percent.
We can imagine that these molecules are like super-tiny balls moving at different speeds and in different directions.
If this gas was in a container, some of the molecules would collide with the wall, bounce off of it, and change direction.
This change in motion means that each molecule exerts a small force on the wall.
(A bigger wall or container will experience more collisions and a greater overall force.)

One way we describe the motion of gas molecules is to think about the force per unit area.
This is the pressure of the gas:

Illustration: Rhett Allain

If you measure the force in pounds and the area in square inches, you get pressure in pounds per square inch, or psi.
That's the most common unit for tank pressure in the United States.

Another unit is the bar, where 1 bar is equal to 14.5 psi.
The value of 1 bar is very close to the pressure of air on Earth.
The atmospheric pressure of the air that surrounds you right now is probably 14.5 psi.
(Yes, I said "probably" because I don't want to judge you.
Maybe you are reading this from the top of Mount Everest, where the pressure is just 4.9 psi, because there is less air above you pushing down.
If so, send me a picture.) In terms of force and area, it is equal to 100,000 newtons per square meter.

Water is also made of tiny moving molecules that act like balls, and those molecules collide with underwater objects (like people), producing pressure.
Water has many more molecules than the same volume of air, which means there are more collisions to produce a greater pressure.
But just like going to the top of Mount Everest decreases the air pressure, going deeper in water increases the pressure, because gravity pulls downward on the molecules of water.
For every 10 meters of depth, the pressure increases by 1 bar, or 14.5 psi.
That means that on a dive 20 meters (around 60 feet) below sea level, there would be a water pressure of 43.5 psi, three times greater than the air pressure at Earth’s surface.

(The fact that pressure increases with depth prevents all the ocean’s water from collapsing into an infinitely thin layer.
Since the pressure is greater the deeper you go, the water underneath pushes up more than the water above it pushes down.
This difference compensates for the downward gravitational force, so the water level stays constant.)

It might sound like 43.5 psi is too much for a person to handle, but it's actually not that bad.
Human bodies are very adaptable to changes in pressure.
If you have been to the bottom of a swimming pool, you already know the answer to this pressure problem—your ears.
If the water pressure on the outside of your eardrum is greater than the pressure from the air inside your inner ear, the membrane will stretch, and it can really hurt.
But there is a nice trick to fix this: If you push air into your middle ear cavity by pinching your nose closed while attempting to blow air out of it, air will be forced into this cavity.
With more air in the inner ear, the pressure on both sides of the membrane will be equal and you will feel normal.
This is called "equalization," for hopefully obvious reasons.

There's actually another air space that you need to equalize while diving—the inside of your scuba mask.
Don't forget to add air to it as you go deeper, or that thing will awkwardly squish your face.

There is one other physics mistake a diver could make.
It's possible to create an enclosed air space in your lungs by holding your breath.
Suppose you hold your breath at a depth of 20 meters and then move up to a depth of 10 meters.
The pressure inside your lungs will stay the same during this ascent, because you have the same lung volume, and they contain the same amount of air.
However, the water pressure outside of them will decrease.
The reduced external pressure on your lungs makes it as though they are overinflated.
This can cause tears in lung tissue, or even force air into the bloodstream, which is officially bad stuff.
 

Buoyancy

There's another problem to deal with when you are underwater: floating and sinking.
If you want to stay underwater, it’s useful to sink instead of float—to a point.
I don't think anyone wants to sink to such depths that they never return.
Also, it’s nice to be able to float when you’re at the surface.
Luckily, scuba divers can change their "floatiness" for different situations.
This is called buoyancy control.

Things sink when the downward-pulling gravitational force is greater than the upward-pushing buoyancy force.
If these two forces are equal, then the object will be neutrally buoyant and neither rise nor sink.
It's like hovering, but in water, and it is essentially what you want to do when scuba diving.

Water actually has neutral buoyancy.
Yes, water floats! Suppose you have a cubic volume of water that’s 1 meter on a side, and it’s in the middle of more water.
We know that this water will just stay there, which means that the upward buoyancy force and the downward gravitational force must be equal.

Now replace that cubic meter of water with a rock of the same shape and size.
Since the buoyancy force is due to the interaction between the object and the water surrounding it, this rock will have the same buoyancy as the cube of water.
However, since it has a greater mass (and therefore weight) than the water, the total force on it will be downward and it will sink.

We can expand this to any generic object to say that the buoyancy force on something is equal to the weight of the water that it displaces (some volume V).
It's useful to think about the mass per unit-volume of water.
We call this the density.
(Physicists like the symbol ρ for density.)

Illustration: Rhett Allain

Since the weight of the displaced water depends on the density of water (ρw) and the gravitational field (g), we get the following expression for buoyancy:

Illustration: Rhett Allain

The weight of an object depends on the density, too.
If the density of that object is less than water, then the buoyancy force will be greater than its own weight and it will float.
Most wood has a density lower than water, so it floats.
A metal boat can float because it's not solid metal—the air inside makes its density lower than that of water.
Also, very small rocks, a great gravy, and cider might float.
(If you don't know that quote, I won't judge you.) On the other hand, an iron nail has a density that’s greater than water’s, so it will sink.

But now we have an idea of how a scuba diver can control buoyancy.
If you increase your volume (and your mass stays the same), then your density will decrease.
This will increase your buoyancy force and you will rise.
Decreasing your volume will decrease your buoyancy force, and you will sink.
You can actually change your volume underwater just by breathing.
Inhaling from a scuba regulator will make your lungs expand, which increases your volume and your buoyancy.
Exhaling does the opposite.

Scuba divers also wear an exterior device to change their volume.
It's basically an inflatable bag that you wear on your back called (not surprisingly) a buoyancy control device.
It connects to a scuba tank so that you can add or remove air to change your buoyancy.

Thermal Conductivity

When the air has a temperature of 72 degrees Fahrenheit, it feels quite nice.
But have you ever been in water at the same temperature? Oh boy, that stuff feels super cold.
Really, the difference is not the temperature, but rather how fast thermal energy transfers from your body to something else.
That’s called thermal conductivity, or the rate that thermal energy can transfer between two objects.
(In this case, from your body to the colder water.)

Here's another example: Suppose you have a wood block and a metal block sitting at room temperature—they’re not in direct sunshine nor sitting on a heater.
If you touch both blocks, the wood will feel warmer than the metal, even though they are actually at the same temperature.
This is because metal has a higher thermal conductivity than wood.
The hand touching the metal will decrease in thermal energy faster, making that one feel colder.

The exact same thing happens with scuba diving.
Since water is a much better thermal conductor than air, the rate that thermal energy moves from your body—which is almost always warmer than the water—to the water is faster than the same process in the air.
In fact, you can lose energy so fast that it's very possible to decrease your core body temperature, which can cause problems like loss of muscle function and even respiratory and heart failure.

The most common solution to this water problem is to wear a wetsuit, which is usually made of a material like neoprene with a very low thermal conductivity.
This decreases the rate at which the human body loses thermal energy.
It's called a wetsuit because you still get wet: Exterior water gets trapped in between your skin and the tight-fitting suit, and your body warms it up.

If you don't like being exposed to water, you could get a dry suit, which has watertight seals on the wrists and neck, and built-in boots, so that water doesn't get in at all.
(OK, maybe just a few tiny leaks.) This does add an extra task for the diver, though.
As you descend to greater water pressures, the air inside the suit will decrease in volume, causing a “shrink-wrap” effect on the body, so that there is no space inside of the suit to bend your arms and legs.
You can fix this by adding air to the suit at greater depths—but you also have to let that air out when you go back up toward the surface.

Underwater Vision

I've been on some dives in murky water where I really couldn't see much.
Spoiler alert: It wasn't very fun.
The point of diving is to see cool stuff underwater.
But even in clear water, you need a mask in order to really see anything.
The mask creates an air space between your eyes and the water, which is what they need to properly focus.
Here's how the lens in your eye works when you're on land, as humans are meant to be, compared to what happens in water:

Illustration: Rhett Allain

A lens bends light based on its shape, as well as the difference in the speed of light in both the lens material and outside of it.
(We can describe the speed of light in a material with the index of refraction.) The speed of light in water is only 66.7 percent the speed of light in air.
That's a problem, as it makes the lens in your eye less able to bend the light to focus on your retina.
The result is blurry vision.

When you put on a mask, you once again have air in front of your eyes, which allows your lens to bend the light the proper amount.
But light is still traveling through the water at a slower speed than it does through air.
When light goes from one medium (like water) into another medium (like air), the light's path bends.
We call this refraction, and it can make things underwater appear closer than they actually are.

How does this work? It's important to remember that we see things because light reflects off objects and then into our eyes.
Take the example of a fish you spot on your diving trip.
Rays of light bounce off the fish, travel through the water and then into the air inside the scuba mask.
Because of the difference in the index of refraction between air and water, the light rays bend.
But our eyes and brain don't know that the light changed directions.
They just assume that it traveled in a straight line, as it does in the air.
This makes it appear that the light came from a spot that is closer than where the fish actually is.

This diagram should help:

Illustration: Rhett Allain

There's another issue with seeing fish (and especially coral) underwater: color.
Although we like to think that water is transparent, it's only sort of transparent.
If you have pure water, visible light will be absorbed as it travels through it.
After 300 meters, essentially none of the light will be left.
That means even in the clearest water, it would be as dark as night at a depth of 300 meters.
(You shouldn't be scuba diving that deep, anyway.)

The absorption of light isn't the same for all colors.
Almost all red light will be absorbed after only 5 meters of water.
As you go deeper, you will only see light that is more blue than red.
Without red light, red things, including fish and coral, will seem to be dark gray.

But you can fix this problem with a simple trick: Bring a flashlight.
The light from your flashlight doesn't have to travel as far as light from the surface before it reflects off that pretty fish, so you can still see the red parts.

Partial Pressure of Gases

Recall that air is normally a mixture of 79 percent nitrogen and 21 percent oxygen at a pressure of 1 atmosphere (1 ATM).
But we need to think about oxygen and nitrogen differently, since they interact with the body in different ways.
We can deal with gas mixtures using the idea of “partial pressure.” Air at 1 ATM (with a mixture of oxygen and nitrogen) is the same as oxygen at a pressure of 0.21 ATM (21 percent of the mixture) and nitrogen at 0.79 ATM.

Let’s look at how both of these gases impact the body.
I’m going to start with the partial pressure of oxygen, which we often just call PPO2.
People need oxygen, but not too little or too much.
Say you’re traveling in a plane at high altitude, where the air pressure is lower.
If you get to a PPO2 below about 0.17, it’s just not enough oxygen for your brain to function.
You won’t be able to think straight, and you might even pass out.
(This is why high-altitude aircraft have pressurized cabins; if they don't, people have to wear supplemental oxygen masks.
It’s also why the flight attendants in a commercial airliner go over safety procedures in the event of a decrease in cabin pressure.)

But underwater, the problem is likely to be too much pressure.
If the partial pressure of oxygen gets around 1.6 ATM, it can cause people to have convulsions.

How do you get a PPO2 that high? Consider the following case: You have a tank with pure oxygen (and no nitrogen) and you dive to a depth of 10 meters.
In order to actually breathe from a scuba regulator, the pressure delivered to your lungs must be equal to the ambient pressure, or you wouldn't be able to inhale.
That means the pure oxygen will be at 2 ATM.
(Remember, you get 1 ATM of pressure for every 10 meters of depth.) Breathing this would produce a PPO2 of 2.0—which is greater than 1.6 ATM.
So, don’t do that.

This is why scuba divers don't use pure oxygen and instead use normal air that’s only 21 percent oxygen.
Its PPO2 at that same depth would be 0.42 ATM, which is not likely to cause problems.
Also, it's much easier to just pump regular air into tanks.
Using other mixtures involves complicated stuff like compressions and the kind of oxygen tanks you see in hospitals.

Now suppose you put a custom mix of gas in your tank.
How about 40 percent oxygen and 60 percent nitrogen? (Note: This is real stuff, it's called Nitrox.) This increases the ratio of oxygen to nitrogen, above what’s in air.
If you breathe this gas at a depth of 20 meters, which is 3 ATM, the oxygen would be at PPO2 of 0.4 × 3 ATM, which equals 1.2 ATM.
This is getting close to a PPM of 1.6 ATM, so maybe you shouldn't go any deeper than that with this gas mixture.

What is the advantage of adding extra oxygen to your tank if you can't go as deep? The answer is that increasing the oxygen decreases the nitrogen.
Although your body doesn't use nitrogen gas, it does get absorbed by your tissues.
When you go to lower pressures (like when coming up to the surface), this nitrogen comes out of your tissues, which is called outgassing.
If too much nitrogen comes out too fast, it will form bubbles that get in your blood and cause serious medical problems.
This is commonly called decompression sickness, or the bends.
Using less nitrogen will mean your tissues absorb less, giving you a lower chance of decompression sickness.

You can also prevent decompression sickness by moving to shallower depths very slowly.
For recreational dives, the goal is to only absorb an amount of nitrogen that can be safely outgassed in the time it takes to swim back to the surface.

The actual calculation for the time you can stay at a certain depth is complicated, and it relies on rough estimations about the average human body.
This is why most modern scuba divers use small dive computers that constantly calculate the time they have remaining based on the depth and time.

That’s not enough physics for you to actually go on a scuba dive, but it's enough to give you a sense of what's going on.
If you’d like to try it out, a dive instructor at a scuba shop can help you learn the rest.
Just remember to bring your flashlight.

3 weeks, 15 unmanned systems: Navy launches ‘Digital Horizon’ exercise in Middle East

From Breaking Defense by Justin Katz

Various unmanned systems sit on display in Manama, Bahrain, Nov. 19, prior to exercise Digital Horizon 2022.

(U.S. Army photo by Sgt. Brandon Murphy)

 

The event will feature 15 unmanned systems, 10 of which will be operating with the Navy in US 5th Fleet for the first time.

 

The US Navy is launching today a three-week event in the Middle East focused on employing artificial intelligence and 15 different unmanned systems, many of which the service will operate in the region for the first time.

 

One spot for the test with the GeoGarage platform

The event, called Digital Horizon, is being hosted by Task Force 59, a group established by US 5th Fleet in September 2021 and tasked to experiment with how the service can incorporate unmanned systems into operations.

Vice Adm. Brad Cooper, the officer leading 5th Fleet and overseeing the task force, has said he aims to have 100 unmanned surface vessels operating in the region by next summer.

The exercise in its current form has taken place at least once before in December 2021.

 

“By harnessing these new unmanned technologies and combining them with artificial intelligence, we will enhance regional maritime security and strengthen deterrence,” Cooper said in a Navy statement about Digital Horizon.
This year’s exercise will feature 17 companies that collectively bring 15 “different types of unmanned systems, 10 of which will operate with US 5th Fleet” for the first time, according to the Navy statement.

Some of the systems participating include Aerovel’s Flexrotor and Shield AI’s V-BAT unmanned aerial vehicles as well as Elbit Systems Seagull, MARTAC’s T-38 Devil Ray and Saildrone’s Explorer unmanned surface vessels.

 

courtesy of Martac in Bahrein

The latter USV became a point of international contention earlier this year when Iranian military and paramilitary forces temporarily pulled some US-owned Saildrones out of the water, accusing the US Navy of abandoning the “spying” vehicles.

Following both incidents, a spokesman for the US Navy dismissed Iran’s claims, saying the Saildrones kept appropriate distances from other vessels and were unarmed and taking unclassified photos of the environment.

The service was ultimately able to recover the drones.

In addition to contributing vehicles, several companies involved in the exercise will also incorporate artificial intelligence and data analytics systems.

“Industry partners Accenture Federal Services and Big Bear AI will also employ data integration and artificial intelligence systems during the event, and Silvus Technologies will provide line-of-sight radio communications while an unmanned surface vessel from Ocius participates from off the coast of Western Australia,” according to the Navy statement.

Capt. Michael Brasseur, commander of Task Force 59, added that industry is working with the service in “one of the most difficult operational environments… I am extremely proud of the entire team, including our many partners across government, academia, and industry for their commitment to Digital Horizon, as we discover new capability together.”

Links :

• Maritime Executive : U.S. Conducts Exercise Preparing for First Unmanned Surface Fleet

Great Lakes extruded bathymetry

Mapbox's William B Davis has created an awesome demo map showing the bathymetry of the Great Lakes in 3D.

His Great Lakes Extruded map actually allows you to virtually dive in and out of Lake Superior, the largest freshwater lake in the world.

source : GoogleMapsMania

 

Building Bahrain

August 17, 1987

 

August 17, 2022

From NASA

Bahrain is a small country with a big population.

Both have been growing larger in recent decades.

Since the early 1980s, the population of this island nation in the Persian Gulf has quadrupled. In 2022, it reached 1.5 million.

As population density has increased and urban development has spread, the need for land has grown.

“Like other countries in the [Persian] Gulf, rapid population growth and the simultaneous increase in urbanization, along with land scarcity, has pushed Bahrain to invest in mega land reclamation projects to extend its coastline,” said Eman Ghoneim, a physical geographer at the University of North Carolina Wilmington.

 

Visualization with the GeoGarage platform (UKHO raster map)

 

These images show changes across 35 years.

The first image was captured by the Thematic Mapper on Landsat 5 on August 17, 1987.

The second image, captured by the Operational Land Imager (OLI) on Landsat 8, shows the same area on August 17, 2022.

In 1987, Bahrain Island had just recently been linked to Saudi Arabia via the King Fahd Causeway, which opened in 1986.

In July 2022, a record 2.5 million motor vehicle passengers traveled on the 25-kilometer (16-mile) stretch of road, according to news reports.

 

August 17, 1987 - August 17, 2022

 

Change is most apparent in the country’s north, where shallow coastal waters have made it technically and economically feasible to build new land from the seafloor.

Notice the areal expansion of existing islands, as well as the addition of new ones.

Sabah Aljenaid, a geographic information systems and remote sensing scientist at Arabian Gulf University, used Landsat images to classify changes to the land between 1986 and 2020.

Aljenaid and colleagues found that built-up (urban) areas dominated the changes during this period, increasing on average by 7.5 percent each year.

 

GB303790 ENC The Gulf - North Eastern Qatar and Ra's Tannurah(1:90,000)

 

BH51501B ENC  Mina' Salman and Approaches (1:12,0000)

 

BH51504B ENC  Approaches to Port of Sitrah (1:12,000)

The growth came primarily at the expense of vegetated land and wetlands.

Aljenaid pointed out the dramatic expansion of Muharraq Island, which now spans more than 60 square kilometers (23 square miles) northeast of Manama, the capital city.

She also pointed to changes on the island of Nabih Saleh, which has lost its agricultural areas.

While urban expansion has been focused in the north, parts of the southern coastline have undergone change, too.

Dredging for the artificial islands of Durrat Al Bahrain began in 2004; by 2007, about 5 square kilometers (2 square miles) of land had been added to Bahrain’s southeast coast.

“A decade ago, I wrote that 11 percent of the island of Bahrain is reclaimed land, and the growth continues today,” said John Burt, a marine biologist at New York University Abu Dhabi.

The shape of Bahrain in 35 more years remains to be seen.

“There was on-and-off again talk of building a bridge across Fasht Al Adhm to Qatar,” Burt said.

“It has not come to fruition, but it may be a future mega-development to watch out for.”

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen.

NASA Study: rising sea level could exceed estimates for U.S. coasts

In the next few decades rising sea will lead to increased storm and tidal flooding for millions of Americans in coastal communities.
Norfolk, Virginia, is pictured here with an inundated roadway.

Credits: City of Norfolk

From NASA by Jane J. Lee

New results show average sea level rise approaching the 1-foot mark for most coastlines of the contiguous U.S. by 2050.
The Gulf Coast and Southeast will see the most change.

By 2050, sea level along contiguous U.S. coastlines could rise as much as 12 inches (30 centimeters) above today’s waterline, according to researchers who analyzed nearly three decades of satellite observations.
The results from the NASA Sea Level Change Team could help refine near-term projections for coastal communities that are bracing for increases in both catastrophic and nuisance flooding in coming years.

Global sea level has been rising for decades in response to a warming climate, and multiple lines of evidence indicate the rise is accelerating.
The new findings support the higher-range scenarios outlined in an interagency report released in February 2022.
That report, developed by several federal agencies – including NASA, the National Oceanic and Atmospheric Administration (NOAA), and the U.S.
Geological Survey – expect significant sea level rise over the next 30 years by region.
They projected 10 to 14 inches (25 to 35 centimeters) of rise on average for the East Coast, 14 to 18 inches (35 to 45 centimeters) for the Gulf Coast, and 4 to 8 inches (10 to 20 centimeters) for the West Coast.

An illustration of the Sentinel-6 Michael Freilich satellite.
Launched in November 2020, it is the latest in a series of spacecraft – starting with TOPEX/Poseidon in 1992 and continuing with the Jason series of satellites – that have been gathering ocean height measurements for nearly 30 years.
Credits: NASA/JPL-Caltech

Building on the methods used in that earlier report, a team led by scientists at NASA’s Jet Propulsion Laboratory in Southern California leveraged 28 years of satellite altimeter measurements of sea surface height and correlated them with NOAA tide gauge records dating as far back as 1920.
By continuously measuring the height of the surrounding water level, tide gauges provide a consistent record to compare with satellite observations.

The researchers noted that the accelerating rate of sea level rise detected in satellite measurements from 1993 to 2020 – and the direction of those trends – suggest future sea level rise will be in the higher range of estimates for all regions.
The trends along the U.S.
Southeast and Gulf coasts are substantially higher than for the Northeast and West coasts, although the range of uncertainty for the Southeast and Gulf coasts is also larger.
This uncertainty is caused by factors such as the effects of storms and other climate variability, as well as the natural sinking or shifting of Earth’s surface along different parts of the coast.

“A key takeaway is that sea level rise along the U.S. coast has continued to accelerate over the past three decades,” said JPL’s Ben Hamlington, leader of the NASA Sea Level Change Team and a co-author of both the new study and the earlier report.

Hamlington noted that the team wanted to determine if they could refine sea level estimates for communities facing imminent changes.
“We’ve been hearing from practitioners and planners along the coasts that they need more information on shorter timescales – looking not 70 or 80 years into the future, but looking 20 or 30 years into the future,” he said.
“The bottom line is that when looking ahead to what we might experience in coming years, we need to consider these higher possibilities.”

This image of Earth shows sea level measured by the Sentinel-6 Michael Freilich satellite in 2021.
Red areas are regions where sea level is higher than normal while blue indicates where it’s below normal.
The satellite collects measurements for about 90% of Earth’s ocean.

Credits: NASA Earth Observatory

Shift in High-Tide Flooding 

 
The hazards of rising sea level are amplified by natural variabilities on Earth.

For instance, by the mid-2030s, every U.S. coast will experience more intense high-tide floods due to a wobble in the Moon’s orbit that occurs every 18.6 years.
Hamlington said that this lunar cycle, in combination with rising sea level, is projected to worsen the impacts of high-tide flooding during the 2030s and 2040s.

Year-to-year variabilities such as the effects of El Niño and La Niña also can make it challenging to forecast how high and how fast sea levels will rise annually.
Hamlington said forecasts will continue to be refined as satellites contribute more data over time.

A visualization tool from NASA’s Sea Level Change Team makes data on future sea level rise from the Intergovernmental Panel on Climate Change easily accessible to the public.
Credits: NASA/JPL-Caltech
See visualization tool

NASA and France’s space agency Centre National d’Études Spatiales (CNES) started jointly flying satellite altimeters in the early 1990s, beginning a continuous space-based record of sea surface height with high accuracy and near-global coverage.
That legacy continues with 2020 launch of the joint U.S.- European Sentinel-6 Michael Freilich mission and its altimeter, which will provide scientists with an uninterrupted satellite record of sea level surpassing three decades.
The mission is a partnership between NASA, NOAA, ESA (European Space Agency), the European Organisation for the Exploration of Meteorological Satellites, and CNES.

NASA sea level researchers have long worked to understand how Earth’s changing climate affects the ocean.
Along with launching satellites that contribute data to the long global record of sea surface height, NASA-supported scientists look to understand the causes of sea level change globally and regionally.
Through testing and modeling they work to forecast how much coastal flooding U.S.
communities will experience by the mid-2030s and provide an online visualization tool that enables the public to see how specific areas will be affected by sea level rise.
Agencies at the federal, state, and local levels use NASA data to inform their plans on adapting to and mitigating the effects of sea level rise.

Learn more about sea level and climate change:
https://sealevel.nasa.gov/

 

Links :

• GeoGarage blog :U.S. coastline to see up to a foot of sea level rise by 2050 / NASA, International panel provide a new window on rising seas

 

The tragic story of the Edmund Fitzgerald, whose crew was never seen again

The Edmund Fitzgerald was lost with her entire crew of 29 men on Lake Superior November 10, 1975, 17 miles north-northwest of Whitefish Point, Michigan.

Whitefish Point is the site of the Whitefish Point Light Station and Great Lakes Shipwreck Museum.

 

From History Defined

 
The Edmund Fitzgerald was a ship that carried cargo across the Great Lakes for over two decades.
Then, on November 14, 1975, the boat sank in a violent storm, taking 29 crew members on board.
The disaster has been the subject of numerous songs and articles and remains one of the most tragic accidents in maritime history.

In this article, we will take a closer look at the story of the Edmund Fitzgerald and explore why its sinking fascinates us all these years later.

 

The Story of The Edmund Fitzgerald: The History

The Edmund Fitzgerald was a Great Lakes freighter that sank in a storm on November 14, 1975, and few understand what happened to cause the freighter to sink.

The ship was carrying a cargo of iron ore pellets weighing about 26,100 tons, and it left from Superior, Wisconsin, heading to the steel mill on Zug Island.
The trip was nothing special, and it was a routine run that the ship had done many times in its 17-year run.
There should have been nothing about the trip that the ship couldn’t handle with its advanced radar and technology.
The trip came at the end of the year, right when the weather was getting colder and the waves were getting higher.

The Edmund Fitzgerald was one of the largest ships on the Great Lakes at the time, measuring 729 feet long, 39 feet tall, and 75 feet wide.
Quite literally, the ship was barely able to pass through the Saint Lawrence Seaway.
It was built with a double-hull design to protect against sinking, and it had a crew of 29 experienced sailors.

This ship was designed to carry these taconite (iron) pellets to ironworks from Duluth to places like Detroit and Toledo.
Still, many are puzzled at how this gigantic boat could have sunken like that when it was made to withstand any water conditions.

Word of an approaching storm from the National Weather Service was announced a gale warning for Lake Superior.

How Storms Affect Lakes And What That Means For Ships

The exciting thing about Lake Superior is that it takes a lot to create big waves.
Even when there are big waves, they don’t usually last long.

The problem with this particular storm was that it was a bit different than typical storms that pass through the area in November and the freighter was in the wrong place at the wrong time.
Ultimately, the storm would generate hurricane-force winds and waves on Lake Superior that would reach approximately 25-35 feet high.
That wouldn’t have been such a problem for the Fitzgerald had the storm not moved consistently and changed the direction of the wind.

The crew altered their course to have land protect them from the giant waves of a storm, but the storm moved and put the freighter directly in the path of the storm and its waves.
Considering the physical size of Lake Superior, storm conditions can be pretty treacherous on the Great Lakes.
Generally, storms can produce steep, short-period waves, which are hazardous to large ships like the Fitzgerald.

But why specifically are waves like this dangerous for larger vessels?

To understand the importance of waves and possibly what happened to Fitzgerald, we need to discuss the concept of waves.
 

How The Great Lakes Can Sink Ships

It’s estimated that over 6,000 ships and 30,000 lives have been lost in the Great Lakes over its history due to how the Lakes affect ships.

Modern vessels can experience these types of dangers in the Great Lakes:

• Cresting Failure: Cresting is when the wave lifts the ship from its middle.

If a boat is caught in a cresting failure, it can cause the vessel to hog.
Hogging is when the waves make the ship bend in the middle, and if it’s bad enough, it can snap the ship in two.

• Ploughing: Ploughing is when the ship’s bow digs into the wave wall in front of it; this can cause the vessel to take on more water and get swamped.

• Ploughing to Ground Strike: This is a more extreme version of ploughing, which happens when the ship’s bow strikes the bottom of the lake.

If this happens, it can cause the boat to sink.

• Bottoming: Giant waves increase the chances of a ship hitting the bottom of the lake.

When this happens, it can damage the hull and cause leaks.

• Wave-Spanning: Wave-spanning occurs when a ship is caught between two waves

When this happens, it can cause the boat to snap in half.
The phenomenon is worse in the Great Lakes because freshwater waves are spaced closer.

• Swamping: Swamping is when a large amount of water comes over the side of the ship, and it can cause the boat to sink.

Especially low ships are at risk of swamping.

The Storm And The Sunken Ship

It was a typical November that year, but around the 8th, storms were forecasted to be in the Fitzgerald’s direct path, and so as the storms grew stronger and approached the Fitzgerald’s planned route, they learned they might have to change course.

This wasn’t a problem as the route would take them north toward the coast of Canada; the northern way would protect them from the massive waves generated by the storm.
Generally, a course change would be all that was necessary, but this storm wasn’t typical.
Unfortunately, the storm constantly moved, changing the wind direction and the waves heights.

By the time the freighter had made it to Whitefish Bay, they were forced to take a more southerly route which put them in danger of the giant waves.
The waves were so big that they started breaking over the ship’s decks, and the water washed over them.

By the time conditions had worsened, the ship had lost a rail, two ventilators, and a radar array.
Eventually, the Fitzgerald lost both radars and was sailing blind.
To make matters worse, the ship was listing to one side and taking on heavy water, more than the two bilge pumps could remove.

Throughout the developing storm, the Fitzgerald communicated with other ships in the area, namely the Anderson and Avafor.
In the late afternoon, the Fitzgerald contacted the Avafor and mentioned that their boat was damaged, naming off the damages and commenting on the dire conditions of the water.

Around 7 PM that evening, the Anderson contacted the Fitzgerald again, noting their location on their radar.
When asked how they were doing, the Fitzgerald responded, “We are holding our own.”
Shortly after, the Anderson lost them on the radar, and no one could contact them.
Unfortunately, the Fitzgerald had quickly sunk, with the crew most likely not realizing the true seriousness of their damage.
The team made no distress call, nor were rescue operations attempted.

A Marine Casualty Report by the United States Coast Guard later determined some factors contributing to the freighter’s sinking.

 

Localization of the wreck on the GeoGarage platform (NOAA raster chart)

 
The Report

The Marine Board of Investigation’s Casualty Report found that the freighter had sunk because of a series of factors, including: The load line may have been lower than seasonally appropriate: When a ship is loaded with cargo, it rests on the water at a certain level, referred to as the load line.
Leaking Hatchways: The cargo was always loaded through a top-side hatchway during the load process.
On October 31, routine damage was noted during an inspection and was scheduled for repair after the shipping season.

The Fitzgerald likely took on the water with these contributing factors when the waves broke over their decks.
The extra weight from the water and the cargo probably caused the ship’s bow to dive into a wave wall and take on too much water.
The load likely rushed forward, plowing the bow into the bottom of the lake and disintegrating the ship.

It’s highly likely that the ship snapped in two and sank quickly, which would have made no time for distress calls or rescue operations.
Upon further inspection, it seems that the lifeboats were ripped from their racks, which is why the remains of two lifeboats were found in the wreckage.

The Sinking Was Likely Preventable

The sinking of the Edmund Fitzgerald is often referred to as a “perfect storm” because all of the conditions had to line up for it to happen.

However, a series of preventable errors and bad luck resulted in the ship’s sinking.
At the same time, November is a difficult time for shipping in this area due to the season shift of the polar jet stream.
Approximately 40% of all Great Lakes shipwrecks occurred in November.

The ship needed repairs that were never made, the load line may not have been appropriate for the season, and they were sailing in an area known for its danger.
While the crew did everything they could to save the ship, in the end, it wasn’t enough.

The Edmund Fitzgerald now rests at the bottom of Lake Superior, and the Coast Guard never recovered its crew.
The story of the Edmund Fitzgerald is a tragedy, but it’s also a reminder of the dangers of shipping on the Great Lakes.

In addition, the mystery of the freighter’s sinking inspired a song by Gordon Lightfoot, which only adds to the legend of this ship.

 

Links :

• Michigan Sea Grant : The storm that sunk the Edmund Fitzgerald 
• Michigan Live : The Edmund Fitzgerald started its tragic journey 47 years ago today
• Duluth News Tribune : Local View: 'In a race with death' 

Tonga eruption confirmed as largest ever recorded

Tsunamis and shockwaves hit continents on the other side of the Pacific.

The Hunga-Tonga Hunga-Ha'apai (HT-HH) volcano was like a massive shotgun blast from the deep, generating the biggest atmospheric explosion recorded on Earth in more than 100 years.

From NIWA

Hunga-Tonga Hunga-Ha'apai (HT-HH) emitted the biggest atmospheric explosion recorded on Earth in more than 100 years.

New Zealand's National Institute for Water and Atmospheric Research (NIWA) has discovered that almost 10km3 of seafloor was displaced – the equivalent to 2.6 million Olympic-sized swimming pools and a third more than initial estimates – with two-thirds coming from the summit and the rest from the surrounding flanks.

Three-quarters of this material was deposited within 20km of the volcano.
This leaves almost 3.2km3 unaccounted for.

 

Earlier this year, a volcano in the South Pacific erupted so ferociously that it was heard from AK, 6,000 mi away.

It unleashed a global tsunami and atmospheric pressure waves that zipped around Earth.

The project leader, NIWA marine geologist Kevin Mackay, said this missing debris could be partly explained by aerial loss.
“This is why we didn’t notice the loss until we had mapped everything.
The eruption reached record heights, being the first we’ve ever seen to break through into the mesosphere.
It was like a shotgun blast directly into the sky.
The volume of this ‘shotgun’ plume is estimated to be 1.9km3 of material, which has been circulating in our atmosphere for months, causing the stunning sunsets we saw following the eruption.
This goes some way to explaining why we’re not seeing it all on the seafloor,” said Mackay.

Despite the huge displacement of material, the volcano’s flank remains surprisingly intact.
However, the caldera, or crater, is now 700m deeper than before the eruption.

Further evidence from the caldera shows signs that HT-HH is still erupting.
A robot boat remotely operated from the UK by SEA-KIT International detected active venting from newly formed cones, explaining why glass fragments formed from cooled molten lava were picked up during NIWA’s earlier survey.

NIWA scientists have also unravelled one of the biggest unknowns of the eruption – the pyroclastic flows.
Pyroclastic flows are currents made up of dense lava, volcanic ash, and gases which can reach temperatures of 1,000°C and speeds of 700km/hr.

NIWA collected 150 sediment cores which were sent to New Zealand’s University of Otago and the National Oceanographic Centre in the UK for analysis.
These samples showed pyroclastic deposits some 80km away from the volcano.
But Dr Emily Lane, NIWA Principal Scientist - Natural Hazards, believes they could have travelled even further.
“Eighty kilometres was the end of our survey range, but the pyroclastic flows appear to extend beyond that distance, perhaps as far as 100km away.
They are also what caused both the domestic and international communications cables to break, with the domestic cable now being buried under 30m of eruptive material.
“The sheer force of the flows is astonishing - we saw deposits in valleys beyond the volcano, which is where the international cable lies, meaning they had enough power to flow uphill over huge ridges and then back down again,” said Dr Lane.

On land, the heat from pyroclastic flows creates a frictionless boundary layer which allows them to move so rapidly, like how a puck glides on an air hockey table.

However, Mackay says this is the first time that scientists have observed underwater pyroclastic flows of this magnitude.
“It’s the interaction with water that made this event so unprecedented.
It’s still speculation but the latest science shows that this phenomenon may be more exaggerated under water.
This could be why the pyroclastic flow travelled so far and with such force,” he said.

When heated, water can expand to around 1,000 times its volume.
When you get several km3 of hot magma instantly hitting the cold saltwater, this reaction is supercharged, and all that energy must go somewhere – and the only options are to explode up or sideways out of the volcano.

“While this eruption was large – one of the biggest since Krakatoa in 1883 – there have been others of similar magnitude since then that didn’t behave in the same way.
The difference here is that it’s an underwater volcano and it’s also part of the reason we got such big tsunami waves,” said Mackay.

Volcanic eruption size comparison to HTHH.
[Image: NIWA-Nippon Foundation TESMaP / Lana Young and Mark Tucker]

Dr Lane said that because these volcanos are not just found in the Pacific, but the world over, we must know what happened and why it was so violent.

“The pressure anomaly generated by this eruption supercharged the tsunami so that it was able to travel right across the Pacific and world-wide.
This mechanism meant that it could travel further and faster than our warning systems expected.
The Krakatoa eruption was that last time a volcanic tsunami on this scale occurred,” she said.

The significant reshaping of the seafloor also had dramatic effects on ecosystems in the region.
There was little sign of any animal life on the flanks of the volcano, in deeper water channels, and most of the surrounding seafloor.
However, there were patches of abundant life that had survived the eruption on several seamounts, giving hope for recovery.

This work was done by the NIWA-Nippon Foundation Tonga Eruption Seabed Mapping Project (TESMaP).

Supported by The Nippon Foundation, NIWA and SEA-KIT surveyed over 22,000km2 surrounding the volcano, including mapping 14,000km2 of previously unmapped seafloor as part of The Nippon Foundation GEBCO Seabed 2030 project, which aims to map the world’s oceans by the end of the decade.

Hunga Tonga-Hunga Ha'apai 3D bathymetry map.
[Photo: NIWA-Nippon Foundation TESMaP]

Mitsuyuki Unno, Executive Director of The Nippon Foundation said that this work is vital to understand the science behind these types of events.
“The research has made clear that underwater volcanic eruptions have serious implications for coastal communities around the world.
A huge proportion of the Earth’s population live on the coast, which are already vulnerable to the impacts of climate change, sea level rise, and big storms.
We need to further our understanding of the risks from underwater volcanos so we can better prepare and protect future generations and their ecological environments.”

Jamie McMichael-Phillips, Project Director of The Nippon Foundation GEBCO Seabed 2030 project said that this project highlights the benefits of working in collaboration to collect fundamental knowledge of the ocean seabed.
“TESMaP is a fantastic testament to what can be achieved if we all come together in pursuit of scientific research.
A complete map of the ocean floor is a necessity to protect our planet in line with the UN SDGs and our Seabed 2030 partners play an invaluable role in helping us realise our goal - as demonstrated by the truly collaborative nature of TESMaP."

Ben Simpson, CEO of SEA-KIT said that their technology allowed scientists to undertake a dangerous and vital mission.
“We have been able to add new equipment to our proven X-Class Uncrewed Surface Vessel’s survey platform, such as winch and sensor cage towing capability, showing yet again the potential of uncrewed vessel technology to support and develop our understanding of the ocean.
USV ‘Maxlimer’ provided a low risk, non-invasive survey solution for this challenging location, bringing down both risk and costs and reducing carbon emissions.”

 

Links :

• GeoGarage blog : Surveying the Tonga volcano eruption aftermath  / Tonga eruption discoveries defy expectations  / Tsunami advisories lifted in US after waves hit Tonga ... / NASA shows new Tongan Island made of tuff stuff, likely to ... / New volcanic island unveils explosive past / Image of the week : birth of a new island in Tonga  
• CNN : How ‘seafloor detectives’ uncovered the secrets of the world’s biggest underwater volcano
• BBC : Tonga volcanic eruption reshaped Pacific seafloor