The lower section of the Brenva Glacier is covered in rock - the remnants of earlier rockfalls in November 1920 from the east face of the Grand Pilier d'Angle. These were four separate events, consisting of between 2.4 to 3.6 million cubic metres of rock, which then mobilised a further 7.8 to 9.9 million cubic metres of snow and ice. Four additional pre-20th century rockfall events have also been identified on the Brenva Glacier. These occurred in 1767 AD; the early 14th century; between 426 and 615 AD; and between 2750 and 2350 calendar years BP.: