Todra Gorge in Morocco

In the eastern part of the High Atlas Mountains in Morocco, near the town of Tinerhir, the Todra and the Dades Rivers have carved out a narrow canyon called Todra Gorge (sometimes spelled Todgha Gorge), on their final 40 kilometers through the mountains. The gorge takes its most spectacular form about 15 km from Tinghir. Here, for about 600 meters, the canyon walls closes in to a mere 10 meters from each other, while the sheer and smooth rock walls rise up to 160 meters on each side. It is said that the gigantic rock walls magically change color as the day progresses.

At the bottom of the gorge flows an ice-cold river, which at one point of time, carried great quantities of water which is apparent from the size of the canyon that was carved out of the rocks. The river has since dried up and reduced to a tiny glacier stream. A well-maintained asphalt road leads all the way from Tinerhir to the gorge and beyond it.

The gorge is breathtaking and easy hike by foot with many places to stop and photograph. The robust rock sides with many uneven surfaces provide plenty of opportunities for rock climbing. You can even spend the night here in one of the small hotels and lodges that the locals have set up inside the gorge.


The Island That Only Appears in Spring

Every year, with the coming of spring, thousands of Chinese tourists flock to the The Gorges Reservoir to see an elusive turtle-shaped island rise from the waters of the Muodaoxi River. The event, dubbed ‘spring turtle rising from water’, is celebrated by local residents because turtles are considered auspicious and a sign of longevity.

It sounds like a fascinating natural phenomenon similar to the Jindo Moses Miracle that takes place in South Korea, but in this case the “magic” is man-made. The water level of Muodaoxi River is controlled by the Three Gorges Dam. In spring, the reservoir supplies water to the areas downstream, bringing down the water level and exposing the island.

The appearance of the island depends on the amount of floodwater heading downstream. For nine months out of a year it is either fully submerged or only has its tip exposed. The turtle shape is fully visible when the water level is between 163 and 168 meters. If the water falls to around 145 meters, the rock becomes connected to the mainland, losing its unique shape.

The unique phenomenon has gained widespread popularity in recent years. Once the island appears, word spreads quickly, and thousands of tourists rush to click photographs from the nearby hills. “It’s a popular saying around here for the arrival of spring, we just say the turtle is coming,” said local resident Meng Liu.


Cross Seas - When Two Waves Meet

This strange pattern at sea is what happens when two wave systems cross each other at nearly perpendicular angles. This can occur when waves generated by one weather system collides with waves generated by another weather system, usually at a place that is far away from both weather systems.

Waves can travel thousands of kilometers over the surface of the water. Even on the calmest days, storms raging elsewhere on the ocean create rolling waves that radiate away from the storm and washes the shore of distant land. These are called swells, which is different from ocean waves raised by the local wind. Another term for wind waves generated and affected by local winds is “wind sea”. All swells start as wind sea, but after a while the wind ceases to blow and the waves have travelled so far out that it’s no longer generated or significantly affected by the local wind at that time. Then it becomes a swell. When two swells coming from two different directions collide, we get “cross seas”, which is what is happening in this picture.

A “cross sea” or “cross swell” observed at Île de Ré off the west coast of France near La Rochelle.

The above picture is very unique, but cross seas are more common than you think. Sea waves and one or more systems of swell waves are frequently present at the same time. However, they might be difficult to distinguish if the angle between their direction of approach is shallow, in which case they might appear to come from essentially the same direction. Besides, swells gradually lose energy the further out they travel. As the swell wave advances, its crest becomes flattened and rounded and its surface smooth. In such condition a swell might be difficult to perceive.

Another reason why such a perfect grid-shaped cross sea is seldom seen is because of the presence of strong local wind that generates wind waves on top of the swell. This wind can be blowing from any direction and has the potential to break the well defined shape and direction associated with swells.

Finally, a cross sea can only been seen from afar or from the air. They are not easily visible from the beach. Here are a few examples that I have managed to find on the web.


Pupil Shape Linked to Animals' Ecological Niche

Take a close look at a house cat's eyes and you'll see pupils that look like vertical slits. But a tiger has round pupils — like humans do. And the eyes of other animals, like goats and horses, have slits that are horizontal.

Scientists have now done the first comprehensive study of these three kinds of pupils. The shape of the animal's pupil, it turns out, is closely related to the animal's size and whether it's a predator or prey.

The pupil is the hole that lets light in, and it comes in lots of different shapes. "There are some weird ones out there," says Martin Banks, a vision scientist at the University of California, Berkeley.

Can you guess which eyes belong to what animal? Top row, from left: cuttlefish, lion, goat. Bottom row, from left: domestic cat, horse, gecko.

Cuttlefish have pupils that look like the letter "W," and dolphins have pupils shaped like crescents. Some frogs have heart-shaped pupils, while geckos have pupils that look like pinholes arranged in a vertical line.

Needless to say, scientists want to know why all these different shapes evolved. "It's been an active point of debate for quite some time," says Banks, "because it's something you obviously observe. It's the first thing you see about an animal — where their eye is located and what the pupil shape is."

For their recent study, Banks and his colleagues decided to keep things simple. They looked at just land animals, and just three kinds of pupils. "We restricted ourselves to just pupils that are elongated or not," Banks explains. "So they're either vertical, horizontal or round."

The researchers gathered information on 214 species. They noted the pupil shape and the location of the eyes on the head, plus the animal's lifestyle. For example, was it predator or prey, and active during the day or night?

One of the researchers, Bill Sprague, also at the University of California, Berkeley, says some animals have such dark eyes, it's hard to even see the pupil.

An Akhal-Teke horse, from Turkmenistan, has horizontal slits for pupils, while the Mediterranean house gecko has vertical slits that look like a series of pinholes.

"I remember one in particular was the hyena," says Sprague. "It actually has a vertical pupil but it's very difficult to judge unless you work with them."

When they pulled everything together, a clear pattern emerged. In the journal Science Advances, the scientists report that there's a strong link between the shape of an animal's pupil and its way of life.

"If you have a vertical slit, you're very likely to be an ambush predator," says Banks. That's the kind of animal who lies in wait and then leaps out to kill. He says these predators need to accurately judge the distance to their prey, and the vertical slit has optical features that make it ideal for that.

But that rule only holds if the animal is short, so its eyes aren't too high off the ground, Sprague says.

"So for example foxes, in the dog lineage, have vertical pupils, but wolves have round pupils," he says.

And while a small pet cat has vertical slits, Sprague says, "the larger predators, like lions and tigers, have round pupils."

In general, round pupils seem to be common in taller hunters that actively chase down their prey, says Banks.

Meanwhile, he says, if you're the kind of animal that gets hunted, "you're very likely to have a horizontal pupil" and to have your eyes on the side of your head. That makes sense, he says, because it gives prey animals a panoramic view, so they can best scan all directions for danger.

But then the scientists began to wonder. This trick would only work if the animal's pupils were parallel with the horizon. And creatures like horses and sheep are constantly pitching their heads down to graze. When the researchers went to watch the animals in action, they discovered something unexpected.

"When they pitch their head down, their eyes rotate in the head to maintain parallelism with the ground," says Banks. "And that's kind of remarkable, because the eyes have to spin in opposite directions in the head."

"I've spent a lot of time handling horses, and having them put their head down to eat, and up to look around, and so on, and I had never noticed this," says Jenny Read, a vision scientist at Newcastle University in the United Kingdom. "It's just an ordinary observation that anyone could make, and yet apparently it wasn't known to science."

Read wasn't on the research team, but she says its conclusions seem right to her. "I think they're the first people to come up with a convincing explanation," she says, "for why the orientation should be chosen differently depending on your ecological niche."

Now, all of this isn't just important to scientists. Novelists and movie-makers constantly have to imagine the pupil shape of fictional creatures like Lord Voldemort in Harry Potter, or the dinosaur Indominus Rex in Jurassic World.

Giving their eyes vertical slits may make them look nice and evil, but Read says "I think their paper suggests that's unrealistic, because both of those creatures are sufficiently high off the ground that they probably should have round pupils."