The giant Perito Moreno glacier in the Patagonian region of Argentina is notable for a couple of reasons. First of all, it is one of only three in the area that are not currently retreating. Secondly, it actually advances right the way across a lake, Lago Argentino, forming an ice dam that can reach more than 70 metres above the surface.

The water backs up behind the wall of ice, raising the level of the southern arm of the lake until the pressure becomes so great that the dam collapses. This process repeats in an unpredictable cycle, every four or five years on average, but sometimes much more or less. (The last rupture event, in July 2008, was captured on video.) Notice how the shoreline of the southern part of the lake has a margin of bare rock, indicating the fluctuating water level – unlike the northern part, which has vegetation almost down to the water’s edge.

Perito Moreno is one of 48 glaciers that descend from the 350km-long Southern Patagonian Ice Field, which is the third largest continental ice sheet in the world (after Antarctica and Greenland). Among them are the Upsala Glacier, which flows into the northern end of Lago Argentino. This glacier has shrunk markedly over the past few decades, and Greenpeace has used photos comparing its extent in 1928 and 2004 to highlight climate change.¹

While there is no high-res imagery of Perito Moreno (except for the topmost part), Google does have some stunning close-ups of the Upsala Glacier, showing jagged shadows, huge icebergs and walls of rock scoured clean by the ice, with a sharp line marking the former edge of the glacier. Your geography teacher would love it.

While you’re here, over on the Chilean side of the ice field, check out the Brüggen Glacier², the longest in the southern hemisphere – it’s impressive, even in low resolution, and parts of it have high res too!

Thanks to Cory Lueninghoener. There’s more info at (you guessed it) Wikipedia.

When the Romans invaded Britain in the 1st century AD, they never quite managed to conquer Caledonia – the area now known as Scotland.

We’ll never know whether the Roman army felt it was too much like hard work to defeat the fearsome northern tribes, or were simply under-attired for the fearsome Scottish weather; either way, in AD 122 the Roman Emperor Hadrian ordered the construction of a wall to defend his territory from the lands to the north.

Hadrian’s Wall stretched for 80 Roman miles (73.5 modern-day miles, or 117km), from the Solway Firth (where the wall is still visible) to the River Tyne (where the wall has vanished, but the fort of Segedunum, which marked its eastern end, has been excavated).

Despite being almost 2,000 years old (and having been heavily plundered by the locals for building materials after the Romans left), a surprising amount of the wall can still be seen today. One of the best preserved stretches is near the village of Gilsland. Here you can also see the foundations of the Roman bridge across the River Irthing – although since it was built the course of the river has shifted westwards.

There are an astonishing number of Roman sites in this area, as a look at the Ordnance Survey map shows. Among them are Birdoswald fort; the nicely preserved milecastle 48¹ (right next to the spot where the railway line slices through the wall); and a couple of Roman camps. The shadows on the aerial photography really show up the traces of old structures and ditches, even where there is little else left on the ground.

The wall was not a single structure: at various stages in its history it was extended, and separate banks and ditches added. Among the later additions was the Vallum, consisting of three earth banks separated by ditches, running parallel to the wall a few hundred metres to the south. The surviving stretches also show up well in aerial imagery; if you scroll northwards from this point you can see the wall itself.

In many places, the builders used the natural topography to help create a formidable barrier. One spectacular stretch of wall follows a steep rocky ridge, Highshield Crags.

The low angle of the sun creates some dramatic shadows here – and if you zoom right in, you can see the shadow of a sycamore tree in the hollow between two ridges. This location, known as Sycamore Gap, will be familiar to fans of the film Robin Hood: Prince of Thieves: it’s the spot where Kevin Costner rescued a small boy from the dastardly Guy of Gisbourne.²

Read more about Hadrian’s Wall at Wikipedia. The 84-mile-long Hadrian’s Wall Path National Trail follows the course of the wall, and its website has a great gallery of ground-level photos.

This is the Turning Torso tower in Malmö, which at 190 metres is Sweden’s tallest skyscraper. The most striking thing about this tower is that it appears to be twisted around its axis. It has nine segments of five-story pentagons that are offset from one another, meaning that the topmost segment is set at ninety degrees to the ground floor.

The Turning Torso was designed by world famous Spanish architect, Santiago Calatrava (some of whose work we’ve featured in the past), and represents part of a growing trend for elaborately warped and twisted “torqued towers“.

In San Francisco’s Golden Gate Park the new M.H. De Young Museum was completed in October 2005 – replacing the original building that had been damaged in an earthquake. To prevent damage to the new building, it can move almost a metre thanks to a system of sliding plates and fluid dampers. It’s also entirely clad in copper, which will eventually oxidize, taking on a green colour reflective of the surrounding vegetation.

From many places around the park, the most striking feature of the building is the 44 metre Hamon Tower, the impressive twist of which can be clearly seen from both an aerial and ground-level point of view.

Tower designers aren’t just rotating their towers either – although still under construction in Google’s images, the China Central Television Headquarters building was completed in December 2008, and its design almost defies belief. Especially when you consider that this area is also prone to earthquakes!

Technically the CCTV building isn’t a traditional tower, but rather a “continuous loop of six horizontal and vertical sections covering 381,000 square metres of floor space”. This is probably best summed up by the building’s local nickname – “Big Shorts”.

There are several other torqued towers around the world that are either in planning, or already under construction. However I wonder how many of them will be delayed or cancelled due to the current economic climate?

• 1 World Trade Center, New York City, (formerly known as the Freedom Tower), will have a roof set at 45° from the bottom.
• The Infinity Tower, Dubai, will feature a 90° twist like the Turning Torso, but will be nearly twice the height.
• The Chicago Spire, Chicago, also designed by Santiago Calatrava, will be 160 metres taller than the Sears Tower.
• The Burj al-Taqa, Dubai, will feature a twisted hyperboloid design, and will generate all its own energy.

Finally, check out the totally insane Signature Towers and equally ludicrous Dubai Towers Dubai which are both planned for construction in Dubai.

See the amazing skyscraperpage.com for more jaw dropping future skyscrapers.

Thanks to stephan and Vectoor.

In the heart of the “Pink City” of Jaipur, India exists a centuries-old observatory used for numbering the stars and counting the minutes.

Though outdated in terms of its technological prowess, the stationary instruments at Jantar Mantar continually prove their relevancy in astronomical science, as well as currently holding the record for world’s largest sundial, towering as they do at over 27 metres tall.

The Samrat Yantra, meaning “The Supreme Instrument”, is used for calculating the time of day to the exact second using the position of the dial and the shadow it casts from the sun. If an astronomical observer knew the time it took a prominent star to transition the sky, they could even use the Yantra tell the time at night.

Maharaja Jai Singh II built Jantar Mantar early in the 17th century as one of five such astronomical observatories throughout India. This particular observatory is the largest of the them all and is based upon the observatory built in New Delhi (below). The other three can be found in Ujain, Mathura, and Varanasi.

James has previously put together some instructions for reading sundials on Google Earth – who thinks than can work out the exact time these images were captured?

What is going on here in Grevenbroich, Germany? This shadow appears to be large human heads on a wheel.

It is actually a steel sculpture by George Ettl, entitled Ettlrad, a play on the German word, Schaufelrad, or paddlewheel. According to a translation of the city of Grevenbroich’s website, the wheel symbolizes the wheel of a coal excavator, with human heads rather than shovels.

The sculpture was part of the Landesgartenschau (Regional Garden Show) in 1995, whose principle is, “To heal the earth.” You can really see their smiles in this ground view photo.

Thanks to hati39 for the suggestion.