The Jackobshavn Isbrae glacier reached a speed of 45 meters per day, as recorded in August 2004. Thus, it is the fastest moving glacier that we know of.
The speed was attributed to an influx of warm seawater into Disko Bay, on the west coast of Goenland.
Titanic and the iceberg the size of Belgium
Since then, the glacier has slowed considerably, especially after a very cold period in 2013.

The funny thing is that it is very likely that the Titanic sank when it collided with an iceberg detached from this glacier that holds the speed record. No wonder something like this : the Jakobshavn Glacier drains 6.5% of Greenland’s ice sheet and produces about 10% of all Greenland icebergs. Approximately 35 billion tons of icebergs break off and leave the fjord each year.
Still, it wasn’t the largest iceberg on record that got in the way of the largest ship. That title is held by someone else: on November 12, 1956, the crew of the USS Glacier sighted a tabular iceberg with an estimated area of more than 31,000 square kilometers, that is, more than the area of Belgium.
The iceberg was 335 kilometers long and 97 kilometers wide. They sighted it west of Scott Island, in the Antarctic Ocean.