Complex sentence: A five-year study started in 2004 showed that the glacier had lost an average of 1.5 m between 2004 to 2009, and that there was a 10--11 m loss in average ice thickness from the glacier.
Split into simpler sentences: A five-year study started in 2004 showed that the glacier had lost an average of 1.5 m between 2004 to 2009. It also came to be known that there was a 10--11 m loss in average ice thickness from the glacier.