 suggested event occurred between September and October 1995, when ice velocity in the slower upstream areas of the glacier was recorded to have increased from 20 to 150 m a−1 and then returned to normal in just a 7-week period (Joughin et al., 1996b). However, as velocity change for the faster main trunk of the glacier was not available during this period, uncertainty remains as to the true magnitude of this mini-surge. It was also unclear if the glacier simultaneously advanced during this interval (Joughin et al., 1996b, 1999; Rignot et al., 2001), although it was hypothesized that this acceleration may have caused a substantial increase in ice discharge (Joughin et al., 1996b; Abdalati et al., 2001). Whether this “mini-surge” reflects true surge-behavior at Ryder Glacier is ambiguous and is discussed in more detail in Section Glacier Surging.
C. H. Ostenfeld Glacier
C. H. Ostenfeld Glacier is ~7.9 km wide (Table 1) and has a drainage area of ~14,000 km2. Of the three outlet glaciers draining into Victoria Fjord, it is the largest and has the highest ice discharge (Higgins, 1989; Rignot et al., 2001; Figure 5B).
Limited information is available on past terminus changes at C. H. Ostenfeld Glacier. Over the past two decades, the terminus shows variable periods of advance and retreat (Box and Decker, 2011; Murray et al., 2015). The floating glacier tongue previously extended ~25 km down fjord of the grounding line (Higgins, 1989, 1991). It still has a floating ice tongue, but it is now only 1.5 km long (Table 1). During 1992–1996, the grounding line retreated 500 ± 200 m (Rignot et al., 2001). More recently, an advance of 5.6 km2 occurred in 2001/02, followed by an annual retreat of 20.6 km2 in 2002/03 (Box and Decker, 2011). Between the years 2000 and 2006, the majority of the ice tongue disintegrated (Figures 4G,H), removing an estimated total area of 350 km2 (Moon and Joughin, 2008). Following this, a further 1.2 km retreat occurred (2006–2007; Murray et al., 2015).
Ice velocities have shown little increase between 2000/01 and 2005/06 (Joughin et al., 2010a) and were consistent with earlier velocity values from 1978 and the 1990s of around 800 m a−1 (Higgins, 1989, 1991; Rignot et al., 2001). Consequently, ice tongue collapse appeared not to significantly affect up-glacier ice velocities during 2000–2006. This could be due to its fragmented nature (Figure 4G), which would provide little resistive stress to the grounded inland ice. There are no documented surges at C. H. Ostenfeld Glacier although a large advance followed by retreat between 2000 and 2003 could suggest surge activity, but this remains untested.
C. H. Ostenfeld is one of the main outlet glaciers in northern Greenland. A large area of its floating tongue has been lost over the past two decades, yet ice velocities have changed little. However, it has recently lost the majority of its floating ice tongue and it may soon retreat back to become grounded, and then discharge grounded ice into the ocean. Thus, there is potential for enhanced velocities and ice discharge from the C. H. Ostenfeld catchment in the near-future, but large uncertainty remains on the glacier's current and future behavior.
Harder and Brikkerne Glaciers
Harder and Brikkerne are two outlet glaciers also draining into Victoria fjord (Figure 5B) which are 5.1 and 6.1 km wide, respectively (Table 1). Collectively, they drain an area of ~3000 km2 (Table 1) from local ice domes. Both glaciers previously coalesced with the floating tongue of C. H. Ostenfeld, with Harder Glacier merging on the eastern side. Brikkerne Glacier sits further north, has three branches, and a small floating ice tongue which is 1.2 km long (Table 1).
Little record of these glaciers exists in the literature and there are no records of terminus change at Harder Glacier. At Brikkerne, the only frontal position data available show that the northern and central sections of the glacier advanced 11 and 8 km, respectively, between 1953 and 1978 (Higgins, 1991). Data from the 1970s showed relatively low velocities at Harder Glac