A record-shattering cold spell has gripped parts of the United States. Much of North America is in the midst of a polar vortex - a system of dense air which produces freezing temperatures and normally sits in the Arctic during the winter months. This has caused a blanket of severe snow and ice, bringing some towns and cities to a standstill and causing travel chaos in others.
Above: Ice chunks and water flow over the falls Niagara Falls, Ontario. The frigid air and "polar vortex" that affected about 240 million people in the US and southern Canada will depart during the second half of this week, and a far-reaching January thaw will begin
Click or swipe for more of Americas' big freeze, captured on camera