Usually icebergs are white because they are made of compressed snow, which reflects all frequencies of visible light. However, if high pressures squeeze the flakes together, or sea water freezes, the gaps between the snowflakes disappear.

Now and then, an iceberg flips over, allowing us to see what has happened to its lower reaches. Most often this occurs when the iceberg has just calved, but occasionally it transpires later, for example in a storm.

When visiting Antarctica at the end of last year, filmmaker Alex Cornell came across the aftermath of one such event.

Cornell has also provided this comparison of an ordinary iceberg set against an upturned one.

The entire world is celebrating World Environment Day this year on June 5th. The day was chosen by the United Nations to honor the 1972 UN Conference on the Human Environment.

Every year, a different city or region hosts the World Environment Day with a different theme. In 2010, Kigali, Rwanda hosted World Environment Day and promoted the theme “Many Species. One Planet. One Future.” In 2007, the event was hosted by Tromso, Norway with the theme “Melting Ice – A Hot Topic?”

This year, the host is the island nation of Kiribati and the theme is “Raise Your Voice, Not the Sea Level.”