Tag Archives: nile

The Nile is 30 million years old — and held together by movements in the Earth’s mantle

The River Nile over Cairo, Egypt. Image credits: Fakharany / Wikipedia.

It’s harder to imagine a more imposing river than the Nile. Stretching over 6,650 km (4130 miles) long and serving as an essential water source since time immemorial, the Nile is a lifeline across northern Africa. Ancient Egyptians considered the Nile river to be the source of all life, and believed the river to be eternal.

Recent research seemed to back that idea up — well, maybe the Nile wasn’t eternal, but it was around for a few million years — which is eternal by humanity’s standards.

The Nile has a surprisingly steady path, nourishing the valleys of Africa for millions of years and shaping the course of civilizations. But for geologists, that was weird.

Why is the Nile so steady when rivers (particularly larger rivers in flat areas) tend to meander so much?

Now, researchers at the University of Texas at Austin believed they’ve cracked that mystery, and it has a lot to do with movement inside the Earth’s mantle.

“One of the big questions about the Nile is when it originated and why it has persisted for so long,” said lead author Claudio Faccenna, a professor at the UT Jackson School of Geosciences. “Our solution is actually quite exciting.”

Convection belts in the mantle.

The team traced the geologic history of the Nile, correlating it with information from volcanic rocks and sedimentary deposits under the Nile Delta. They also carried out computer simulations that recreated tectonic activity in the area over the past 40 million years.

They linked the Nile’s behavior to a mantle conveyor belt.

“We propose that the drainage of one of the longest rivers on Earth, the Nile, is indeed controlled by topography related to mantle dynamics (that is, dynamic topography).”

The Earth’s interior is dominated by the mantle, and the mantle is not static. Large swaths of the mantle are moved around by convection. Sometimes, parts of that are pushed towards the surface. This upwelling magma has been pushing up the Ethiopian Highlands, helping to keep the river flowing straight to the north instead of wending its way sideways. This uplift, researchers conclude, is responsible for the gentle and steady gradient that keeps the Nile on a consistent course.

The Nile famously flows steadily to the North. Image credits: NASA.

Getting to this conclusion, however, was not straightforward — and it wouldn’t have been possible without state-of-the-art geophysical modeling. This proved to be the glue that pieced the entire theory together.

“I think this technique gives us something we didn’t have in the past,” said Jackson School scientists Petar Glisovic, one of the authors who is now a research collaborator at the University of Quebec.

As a consequence of this study, the researchers also showed that the Nile must be at least as old as the Ethiopian highlands — so this puts its age at 30 million years, which is several times more than previous estimates.

The study was published in Nature.

River_Nile_map

What is the longest river in the world? That’s surprisingly debatable

Measuring the world’s longest river is actually not as simple as it sounds. The process is far more complicated than finding the source and the mouth then measuring the distance between them. Rivers often join together in river systems making it very difficult to pinpoint where an individual river begins and where it ends.

How do you measure a river? It’s not as simple as using a ruler

Today, most hydrologists agree that the most accepted method is to measure the longest possible along-thalweg continuous distance from the headwaters of the 1st order stream to the mouth of a river. The thalweg is a line connecting the lowest points of successive cross-sections along the course of a valley or river. A 1st order stream is a stream without any tributaries entering. When two 1st order streams meet, they form a 2nd order stream and when two or more 2nd order streams meet, they form a 3rd order stream — and so on. In other words, to find the longest river, you have to measure the length of the longest continuous river channel in a given river system.

That’s still a gross oversimplification because, in practice, things can get very tricky. For instance, for most rivers, the mouth is easy to determine and measure, but for very large rivers like the Amazon, which flows into the ocean, placing the mouth can be less concrete — and can make all the difference in terms of river length. Another example of murky measurement is the Mississippi, whose headwaters are considered by the USGS to be Lake Itasca in Minnesota, yet if its longest tributary is taken into account (the Jefferson and Missouri rivers), it becomes three times as long.

I know what you’re thinking — get to the damn question already.

Well, there are two ways to think about the largest river. One is length, where the Nile takes the crown, and the other is volume, where the Amazon clearly stands out among all other river systems in the world.

The Nile — the longest river in the world

River_Nile_map

According to the U.S. National Park Service, the river Nile is the longest in the world, spanning 4,135 miles (6,650 kilometers). Though it mostly runs through Egypt, from its source in Burundi to its delta on the Mediterranean Sea, the Nile also passes through nine other African countries: Sudan, Eritrea, Ethiopia, Uganda, Kenya, Tanzania, Rwanda, Burundi and the Democratic Republic of Congo.

The biggest lake in Africa, Lake Victoria, was historically regarded as the source of the river Nile. A waterfall known as Ripon Falls on the northern edge of the lake pours water through a narrow opening, which many claim this to be the very beginning of the Nile. But if that’s the case, what’s the source of Ripon Falls? Lake Victoria is surrounded by mountains riddled with streams which tumble down into the lake. The largest tributary of Lake Victoria is the Kagera River, which has its headwater in Burundi. It is from here that the Nile is measured as the world’s longest river.

Some 300 million people depend on this river for their water supply and for food crop irrigation.

There’s even a dam that harnesses the Nile’s energy — the Aswan High Dam. After it was completed in 1970, for some years it used to provide half of the electricity demand of Egypt, though this figure has steadily decreased as the nation increased its electricity demand. It now supplies around 20% of the country’s electricity. The dam also controls summer flooding.

At the other side of the spectrum, officially, the shortest river is the D River in Oregon, USA, which is just 37 meters long.

The Amazon — the largest river in the world by water volume

location-map-amazon-river

Credit: Maps of the World.

It’s not even close: the Amazon is considered the 2nd longest river in the world, spanning 3,980 miles (6,400 kilometers). However, it holds the title of the world’s largest river by volume. On average, 120,000 cubic meters (about 20 swimming pools’ worth) of water flows out of its mouth every second. It contains a staggering 20% of the world’s fresh water supply. Some parts of the river can exceed 120 miles (190 kilometers) in width when the Amazon swells during the wet season. Even in dry conditions, the Amazon is so wide throughout its length that to this day, no bridge spans it.

From its source in Peru, the Amazon, or Rio Amazonas in Portuguese and Spanish, flows mostly through Brazil and empties into the Atlantic Ocean. The Amazon also forms the world’s largest river drainage basin that includes Brazil, Bolivia, Peru, Ecuador, and Colombia.

The source of the Amazon has also been hard to pin down over the centuries. Scientists and explorers have attempted to establish the river’s source ever since the 1600s. Over the years, five rivers in southwestern Peru were given the honor and for nearly a century the headwaters of the Apurímac River on Nevado Mismi was considered as the Amazon’s most distant source. But a 2014 study found it to be the Cordillera Rumi Cruz at the headwaters of the Mantaro River in Peru.

However, some geographers have disputed this — according to them, Mantaro stays dry for about five months of the year when the Tablachaca dam, built in 1974, diverts its water through a 12-mile (20 km) tunnel. And to make the dispute even more interesting, if the Mantaro River really is the source, that would add 47 to 57 miles (75 to 92 kilometers) to the length of the Amazon.

Does being the longest even matter?

In 2007, Brazilian researchers announced they had identified a new source and a new mouth, measuring the Amazon 4,225 miles (6,800 kilometers) long and toppling the Nile as the longest river. The mouth of the Amazon is traditionally thought to be located on the north side of the Marajó Island, which is about the size of Switzerland. The rather hefty area means that the side of the island the mouth is on can matter a lot when measuring the Amazon’s length. The Brazilian study, which was not peer-reviewed and immediately proved controversial, put the mouth on the south side of the island to the Pará River then out into the ocean. After more recent studies, experts seem to agree that, although there’s indeed some of the Amazon’s water in the Pará, the latter river is distinct from the Amazon. The Nile is still king for now, but as new sources are discovered and mouth areas are redefined, the crown could get swapped between the two rivers — and possibly more than once.

At the end of the day, ‘the longest river’ title doesn’t even matter all that much. As the constant juggling of measurements throughout the centuries show, there will always be some researcher or team that will claim they’ve made some more precise readings. And of course they will — the coastline paradox states that measuring something with a complex geometry, such as a coastline is not possible because the length actually increases the more granular the measurement gets. Huh? I know that sounds shocking, but this counterintuitive concept has been proven mathematically and arises from the properties of fractal-like geometries, which includes rivers. Rivers have a lot of curves and the more you zoom in, the more bends and twists you see.

So, keeping the coastline paradox in mind, a lot of scientists have long ago stopped caring about measuring river length. What’s far more interesting and scientific — not to mention a lot easier and precise — is to look at the drainage area, which is an area of land where precipitation collects and drains off into a common outlet, such as into a river or a bay. By this measure, the Amazon is clearly the largest river in the world with a drainage area of 6.3 million square kilometers, while the Nile makes it only to the fifth spot, trailing behind Congo, the Mississippi, and the Ob.

What do you think?

West Nile.

Indiana’s health officials warn of West Nile virus spotted in mosquitoes in Elkhart, Carroll County

Indiana state officials urge locals in Elkhart and Carroll County to take precautions after mosquitoes in the area tested positive for the West Nile virus.

West Nile.

West Nile Virus.
Image via Cynthia Goldsmith (CDC) / Public Domain.

West Nile virus is a mosquito-borne virus known to be present in Africa, Asia, Europe, and the Middle East — and, since 1999, the Americas as well. It’s quite a nasty bug. The milder form of the illness,  West Nile fever, can include fever, headache, body aches, swollen lymph glands, or a rash. More severe forms of the disease affect the nervous system and include inflammation in the brain and spinal cord (encephalitis), meningitis (inflammation of the tissues that wrap around the brain and spinal cord), muscle paralysis, even death.

It generally likes to infect wild birds. Mosquitoes bite infected birds and transmit the virus over to humans. In the US, it was first identified in wild birds in Indiana in 2001; up to now, it has been found in “most states along the eastern coast and east of the Mississippi River,” according to the Indiana State Department of Health (ISDH).

As of June 27, the ISDH released a warning to locals in Elkhart and Carroll County (link goes to the ISDH’s live monitoring of the virus) that the virus has been detected in mosquitoes in the area. State Health Commissioner Kris Box adds that there is no need to panic. No human cases have been detected as of now, and it’s actually not that uncommon for West Nile to be spotted around these parts — it happens every year. The ISDH expects to continue to see increased West Nile activity throughout the state as the mosquito season progresses.

State officials urge residents to take precautions — especially since the risk of infection is highest during the summer months. Some of the ways you can protect yourself from infection with the virus include:

  • Avoid being outdoors when mosquitoes are active, especially late afternoon, dusk to dawn and early morning.
  • Apply an EPA-registered insect repellent containing DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol to clothes and exposed skin.
  • Cover exposed skin by wearing a hat, long sleeves, and long pants in places where mosquitoes are especially active, such as wooded areas.
  • Install or repair screens on windows and doors to keep mosquitoes out of the home.

Residents should also take the following steps to eliminate potential mosquito breeding grounds:

  • Discard old tires, tin cans, ceramic pots or other containers that can hold water.
  • Repair failing septic systems.
  • Drill holes in the bottom of recycling containers left outdoors.
  • Keep grass cut short and shrubbery trimmed.
  • Clean clogged roof gutters, particularly if leaves tend to plug up the drains.
  • Frequently replace the water in pet bowls.
  • Flush ornamental fountains and birdbaths periodically.
  • Aerate ornamental pools, or stock them with predatory fish.

Nile Crocodile enters Florida, researchers find

Scientists from the University of Florida have mate a startling discovery: Nile Crocodiles are now in Florida, infiltrating local populations in the Everglades. They warn that these crocs are extremely dangerous, and can injure or kill humans.

Nile crocodile in Gulu, Uganda. Photo by Tim Muttoo

The Nile Crocodile (Crocodylus niloticus) is an African crocodile and the second largest reptile in the world, after the saltwater crocodile. It can grow up to 5.5 metres (18 feet) in length and was blamed for at least 480 attacks on people and 123 fatalities in Africa between 2010 and 2014. Another report claims that the Nile crocodile kills hundreds of people each year. Either way, this is definitely a species which can be dangerous, much more dangerous than native alligators.

DNA analysis has confirmed that at least three juveniles are part of the Nile species, linked to crocodiles from South Africa. Kenneth Krysko, a herpetology collections manager at the Florida Museum of Natural History told the journal Herpetological Conservation and Biology that the species can survive and potentially thrive in sub-tropical Florida.

“The odds that the few of us who study Florida reptiles have found all of the Nile crocs out there is probably unlikely. We know that they can survive in the Florida wilderness for numerous years, we know that they grow quickly here and we know their behaviour in their native range, and there is no reason to suggest that would change here in Florida.”

Crocodylus niloticus is considered a generalist predator which can feast on pretty much all types of meat. They can certainly adapt to Florida’s environment, munching down birds and mammals. Researchers don’t know where these crocs came from, but pet owners are the likely cause. According to the Guardian, large groups of Nile crocodiles have been imported from South Africa and Madagascar, both for display at places such as Disney’s Animal Kingdom, and to supply Florida’s pet trade.

It’s not the first time Florida is dealing with invasive species; on the contrary, the state is one of the most invaded areas in the world. The spiny lionfish has destroyed reef-dwelling fish across the Caribbean, the Cuban tree frog has also taken out many native specimens, and recently, the Burmese python has become so common that Florida is authorizing python hunts.

“My hope as a biologist is that the introduction of Nile crocodiles in Florida opens everyone’s eyes to the problem of invasive species that we have here in our state,” Krysko said. “Now here’s another one, but this time it isn’t just a tiny house gecko from Africa.”

 

No, the Nile hasn’t turned blood red

It always baffles me how some publish completely misleading clickbait titles. The most recent one is this satellite image of the Nile river, which has reportedly “gone blood red”. Sorry to burst your bubble, but there’s no biblical plague, not even an algae bloom or anything that colored the Nile – it’s simply an image with several spectral bands overlapping, resulting in unnatural colors; this type of visualization helps in monitoring environmental parameters such as vegetation. In other words, the Nile isn’t red, it just looks that way.

The picture was taken by an European Space Agency satellite called Sentinel-3A. The satellite features a variety of high sensitivity instruments that will measure Earth’s oceans, land, ice and atmosphere. Sentinel-3’s Sea and Land Surface Temperature Radiometer (SLSTR) measures the energy radiating from Earth’s surface in nine spectral bands, including visible and infrared. Herein lies the mystery of the red river.

When specific spectral bands are overlapped on top of each other, they can make certain things about the surface stand out. Let’s take for example the normalized difference vegetation index (NDVI), one of the more common ones. The NDVI uses the visible and near-infrared bands of the electromagnetic spectrum to see where there is live vegetation.

This is very similar to what’s visible in the picture – the Nile has some living vegetation growing in and around it, which is why it appears bright red. Here, the satellite combined radiometer and color data. It’s a really cool picture, and one that does a great job at highlighting the usefulness of the satellite. Hopefully, science outlets will appreciate that and refrain from needlessly exaggerating or misrepresenting the facts.

As for Sentinel – it has a big mission ahead of it, and lots of useful data to provide.

‘The launch of Sentinel-3A further expands the fleet of dedicated missions for Copernicus services,’ Philippe Brunet, Director of the European Commission’s Directorate-General for Internal Market, Industry, Entrepreneurship and Small- and Medium-sized Enterprises, said.
‘This mission is particularly important as it will contribute to the Copernicus Marine Environment Monitoring Service and the global land component of the Copernicus Land Service.’