In pictures: Niagara Falls transformed into a frozen wonderland

Tourists have defied extreme temperatures to have a look at the partially frozen Niagara Falls. Visitors are praising the winter spectacle as a striking sight. The partial freezing resulted from a powerful surge of Arctic air driven by disruptions in the polar vortex, a ring of strong winds that typically traps cold air near the North Pole. These iconic pictures, you should not miss.