The Outlet Glaciers

The rates of movement of seven of the major outlet glaciers that discharge ice into the Ross Ice Shelf are listed in Table 19.4 based on measurement by Swithinbank (1963). The observed rates range from 

Glacier Rate of movement (m/d) Width (km) Rate X Width (kmVyear) 

A large deposit of till at the base of Mt. Tuatara on the south side of the Byrd Glacier in Fig. 19.14 a few tens of meters above the present level of the glacier extends up the side of the mountains for about 100 m. The glacial polish of the Shackleton Limestone on Mt. Tuatara indicates that the level of the glacier in the past was several hundred meters above its present level. The elevation of the base of the deposit is about 300 m a.s.l. 

The color of the weathered surface of the glacial deposit on the slope of Mt. Tuatara is yellowish but fresh surfaces are light grey. The till contains abundant striated and faceted clasts of limestone as well as of igneous and metamorphic rocks. In addition, the till is underlain by a lenticular deposit of coarse gravel and contains structures indicative of soft-sediment deformation. No plant or animal fossils were observed perhaps because the till was deposited at the base of the Byrd Glacier and was exposed only when the level of the glacier declined to its present level. 

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The local conditions that affect the weather alluded to above include the katabatic wind that blows from the polar plateau through the valleys of the outlet glaciers in the Transantarctic Mountains. The wind is generated when the layer of cold air that forms directly above the surface of the polar plateau drains downslope toward the coast. The speed of the wind on a gentle slope... 

As time passed, the volume of the East Antarctic ice sheet increased sufficiently to bury the Transantarctic Mountains during the early Miocene until only the highest peaks remained ice-free as nunataks. At this time, the ice deeply eroded the valleys of the outlet glaciers and imposed on them the typical U-shaped cross-sections that are evident in the ice-free valleys of southern Victoria Land and elsewhere in the Transantarctic Mountains. More recently, the East Antarctic ice sheet thinned causing previously ice-covered areas of the Transantarctic Mountains to become ice-free and exposing till of the Sirius Group that was deposited by the ice sheet during its maximum extent. 

The blue-ice areas surrounding the Elephant Moraine are part of the broad ablation belt of the East Antarctic ice sheet located west of the Transantarctic Mountains. In this area the eastward flow of the ice sheet is blocked except for the ice that squeezes through the narrow valleys of the outlet glaciers. Therefore, ablation dominates the glaciological processes that are occurring in this areas and the rate of ablation is an important factor in the mass balance of the ice sheet. 

Fig. 17. 36 The East Antarctic ice sheet loses mass not only by melting of basal ice, but also by means of ice streams and outlet glaciers. For example, the Recovery ice streams which are lubricated by water that originates from the subglacial Recovery lakes transports ice to the Filchner Ice Shelf, whereas the outlet glaciers which cross the Transantarctic Mountains discharge ice into the Ross Ice Shelf and directly into the Ross Sea. Similarly, ice streams that drain the West Antarctic ice sheet contribute most of the ice into the Ross Ice Shelf (Adapted from Bindschadler and Bentley 2002. By permission of the authors and the Editor of Scientific American)...

Evidently, theNeogeneglaciationofthe Transantarctic Mountains and of the McMurdo Sound was a complicated process that combined changes in climate and sea level with the resulting changes in the flow of the outlet glaciers and of the Ross Ice Shelf. 

Mayewski (1975) used the elevations of the lateral moraines to project the level of ice in the outlet glaciers to the East Antarctic ice sheet. The resulting ice-sheet reconstruction indicated that during the Queen Maud Glaciation the Transantarctic Mountains were almost completely covered by ice and that the ice sheet along the central divide in East Antarctica was about 350 m thicker than it is at the present time. In addition, the grounding line of the Ross Ice Shelf moved forward to a position 225 km north of the present edge of the ice shelf. 

Table 19.4 Rate of movement of ice in the outlet glaciers that cross the Transantarctic Mountains and discharge into the Ross Ice Shelf (Swithinbank 1963)...

Retreat of the outlet glaciers caused by thinning of the East Antarctic ice sheet, or by uplift of the Transantarctic Mountains, or by climate change, or all of the above... 

Former residents of McMurdo Station will also recall the windstorms that suddenly reduce visibility to less than 100 ft (30.48 m), with wind speeds in excess of 55 knots (101.9 km/h), and wind-chill temperatures that drop below -100°F (-73.3°C). Under these conditions, all personnel in McMurdo are required to remain in-doors (Condition 1) and all travel is suspended for the duration of the storm that may last several days. The classification of weather conditions detailed in Table 2.3 is the responsibility of the McMurdo Weather Office (Mac Weather). Condition 1 storms can occur anywhere within the Transantarctic Mountains during the austral spring and fall especially on major outlet glaciers, such as the Reedy Glacier in Fig. 2.11, that channel the katabatic winds from the polar plateau to the Ross Ice Shelf or to the Ross Sea. Field parties that experience such storms learn first-hand that weather still rules in Antarctica. 

The central sector of the Transantarctic Mountains extends from the Byrd Glacier south to the mouth of the Shackleton Glacier (Chapter 5 Fig. 3.1). This segment contains thick deposits of Beacon rocks which form several large mountain ranges at the edge of the polar plateau between the major outlet glaciers ... 

Fig. 11.6 The zero isopach contour outlines the Beardmore and the Horlick-Queen Maud glacial basins which are separated by a glacial divide where the tillite is absent or very thin (<1.5 m). The measured ice flow directions are indicated by short and straight arrows, whereas the long and curved arrows mark the locations of the major outlet glaciers (Adapted from IsbeU et al. 2008)...

The elevation of the present ice sheet in East Antarctica in Fig. 17.1 rises from sea level along the coast to more than 4,(X)0 m in the interior at Dome Argus (18°00 S and 77°00 E). The ice moves under the influence of gravity from the interior of Antarctica toward the coast where it either forms icebergs or coastal ice shelves at the outflows of outlet glaciers and ice streams (e.g., the Ross, Renne, Filchner, Amery and other ice shelves). 

The deposits of till and glacial outwash deposits in the Transantarctic Mountains are especially noteworthy because their very existence at sites well above the level of the present outlet glaciers indicates either the thickness of the glaciers that once flowed across the Transantarctic Mountains or the amount of uplift of the mountains relative to a more or less constant thickness of the East Antarctic ice sheet. Therefore, we approach this topic with questions about the age (or ages) of the... 

Ice from the polar plateau still occurs in the Wright Upper and Taylor glaciers, but only the Ferrar and KoettUtz valleys contain continuous outlet glaciers that discharge ice from the polar plateau into McMurdo Sound (Adapted from the Landsat Image Mosaic of Antarctica (LIMA) http //Iima.usgs.gov)... 

We do not know how many times the valleys were filled with ice from the polar plateau and the durations of these glaciations. The Ferrar Valley still contains an outlet glacier that discharges ice into the Ross Sea. The Taylor Valley also contains a former outlet glacier (i.e., the Taylor Glacier) which has retreated up the Taylor Valley (Fig. 3.7). Only Wright and the Victoria valleys are presently largely ice-free. 

A new class of global earthquakes (Ms > 4.5) was discovered and related to giant and catastrophic landslides or phenomena occurring near the front of fast-moving outlet glaciers in Greenland and Antarctica. The xmique... 

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