Megacities

Sixty years ago there were only two megacities - cities with over 10 million inhabitants - on the planet: New York and Tokyo. Now there are 23 and by 2025 the UN predicts there will be 37, all but eight in the developing world. The Guardian has a special interactive report investigating this trend - take a look at it here. Then have a look at the data.
The pictured city Shanghai is home to at least 20 million people, half of whom are immigrants from other parts of China.

Yellowstone Park: Supervolcano

Yellowstone park sits on top of one of the biggest volcanoes on earth - in fact it is a supervolcano that has erupted several times with massive force over the course of the last two million years. Geysers like Old Faithful are a tell-tale sign that volcanic activity is going on just beneath the surface. The Independent published an article on supervolcanoes earlier this year.
Click on the following links from the National Park to find out more about the Yellowstone Volcano.
The ingredients of a geyser.
What is driving the geyser.
Where is the Volcano?
Old Faithful Webcam.

Mount St Helens eruption

Mount St Helens in Washington State in the western United States erupted in May 1980 after two months of earthquakes and steam venting. The eruption caused the entire north face of the mountain to collapse, with the pyroclastic flow destroying everything in its path, melting glaciers on the mountain and then causing massive mud slides (lahars). The volcanic cloud spread across the USA in just three days and encircled the earth in two weeks.  This National Geographic video provides a great introduction to the topic, explaining how volcanoes are formed. Then take a look at this Discovery Channel video about the effects and this clip on the devastating effects of the Mount St Helens eruption.