Â鶹¹ÙÍøÊ×Ò³Èë¿Ú

Val Vannet continues her look at geographical issues from Alaska to Argentina, following the journey being made by Mark Beaumont on his latest adventure, Cycling the Americas...

On the 15th of January in the middle of the southern hemisphere summer, Mark Beaumont set foot on the summit of Aconcagua. At 32 degrees south, Aconcagua is only as far to the south of the Equator as the Mediterranean Sea is to the north yet here is Mark wearing his ice crampons having a very well-earned rest on its snowy summit. He has every right to be looking pleased with himself. After 10 days of climbing, he has just reached the 6963m summit of the world's highest mountain outside Asia. If you've been following the previous geoblogs, you will already know why there is snow in summer at 32 degrees south and why there is a mountain there at all for Mark to climb! If not, you can catch up with the answers.

Although Mark sent some wonderful images of the mountain, it is very difficult to imagine how high Aconcagua really is. The facts tell us it is over five times the height of Ben Nevis with glaciers which descend almost half way down the mountain. Mark talked about the altitude sickness which many climbers suffer on the mountain which made sleeping difficult for him and gave him headaches but nothing really captures how high 6963 metres is until you see a photo like the second below, showing the shadow over the surrounding mountains...

On (where you can browse through all the images Mark has taken on his journey), Mark described this stunning view as follows

"Early morning, just before we climbed into the sunshine, this was the view of the mountain's shadow - showing how much higher it stands than its neighbours"

The idea of how much higher a mountain is than its neighbours is called prominence. A mountain with high prominence is not only high but really stands out in the landscape and so it's a great place to take in the views! Calculating prominence is quite difficult because it involves how close the nearest neighbouring peak is and how low you have to descend before you can climb it. Luckily and this is what is revealed... Not only is Aconcagua the highest mountain outside Asia but it is the second most prominent mountain in the world after Mt Everest. And the third? Well, Mark has been to the top of it too and hopefully you can remember its name. If not, have a look.

Despite the fact that Mark had been climbing through snow on Aconcagua, his return to the foothills of the Andes and to the city of Mendoza brought him back to warm and sunny weather - exactly the sort of weather we'd expect in Mediterranean countries on our summer holidays. No surprise therefore that Mendoza is surrounded by vineyards which produce two thirds of Argentina's wine.

After a brief rest in Mendoza, Mark got back on his bike for the last leg of his journey (which will end in Ushuaia) and headed towards the scrubby grassland plains known as the Pampas. "One of the biggest shocks back on the bike is the heat. Feels hotter than the Atacama out here". What Mark is describing is exactly what we'd expect in summer in areas with a Mediterranean-type climate... and it's great for ripening the grapes!

South into Patagonia, there has been one recurring weather theme - the wind. Lots of Mark's updates and 'tweets' contain something about the wind. Now, if you are a cyclist, wind is great news - so long as it's behind you!

"Stunning day in Patagonia. A whisper of a northerly so excited for more smooth cycling today"

"A blustery 90 miles. If I seem mildly obsessed with wind then it's probably cause I am! Out here it's my best friend & worst enemy in one!"

"Patagonia is stunning - it is windy tho!"

"I know I might have touched on this subject before but its very, very windy today!"

Most of the time the winds in Patagonia are blowing in Mark's favour, coming roughly from the north, 'pushing' him along and helping him to cover the miles that are left. The prevailing winds in this part of South America are actually north westerlies which come in from the Pacific, blow down from the Andes and then cross the flat plains of Patagonia. You can see how flat it is in this image which Mark sent back recently.

Patagonia, like the Atacama in northern Chile, lies in a rainshadow and receives very little rain. If you want to understand rainshadows, you can read about them in the last geoblog. The rainshadow effect explains why most parts of Patagonia receive less than 250mm of rain and so are desert dry.

They are, however, very windy and to conclude this geoblog I am going to direct you to an article on the Â鶹¹ÙÍøÊ×Ò³Èë¿Ú News website which describes - including children in school who may now be able to read this blog because of the wind!

Next time - journey's end.

Val Vannet