when averaged annually, with summer speeds even higher (as measured 2012–2013). The speed of Jakobshavn Glacier varied between per year between 1992 and 2003. The ice stream's speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about per year, or roughly 4 percent of the 20th century rate of sea level rise. Jakobshavn Isbrae retreated from 1850 to 1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining the Greenland Ice Sheet. The glacier terminus region also had a consistent velocity of per day (maximum of per day in the glacier center), from season to season and year to year, the glacier seemed to be in balance from 1955 to 1985. The position of this terminus fluctuated by around its annual mean position between 1950 and 1996. After 1997 the glacier began to accelerate and thin rapidly, reaching an average velocity of per day in the terminus region. On Jakobshavn, the acceleration began at the calving front and spread up-glacier in 1997 and up to inland by 2003. In 2012 a significant acceleration of Jakobshavn was observed, with summer speeds up to 4 times its speed in the 1990s, and average annual speeds of 3 times its 1990s speed. Movement reached more than 17,000 metres per year. Jakobshavn has afterwards slowed to near its pre-1997 speed, with the terminus retreat still occurring until 2015. In 2016, researchers found the water temperatures in its fjord had dropped to levels as cool as those in the 1980s. Airborne altimetry and satellite imagery show that until early 2019, this temperature drop likely caused the glacier to re-advance, slow down, and thicken (by over 100 feet from 2016 to 2018). Large calving events where the glacier produces icebergs have also been found to trigger earthquakes due to ice-ice and ice-bottom of the fjord interactions. and from the longer-duration forces exerted on the solid Earth during the capsize of very large (e.g., > 1 km3) calved ice volumes. Especially large calving events at Jakobshavn have produced glacial earthquakes that are detectable on seismographs worldwide with moment magnitudes in excess of 5.0. A large calving of approximately 7 km2 took place on 15 February 2015. On 16 August 2015 a calving was identified via satellite images as the largest ever recorded at Jakobshavn, with an area