72 MARION EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



water glaciers. Little definite change in the extent or thickness 

 of the inland ice appears in historic records, but there is geological 

 evidence in the position of erratics around Disko to indicate that 

 glaciation was once much stronger there than it is to-day. Tlie 

 marginal advances and retreats of the inland ice are slow with no 

 two localities exhibiting exactly the same characteristics. Jacob- 

 shavn Glacier, in Disko Bay for example, has, except for one 

 interruption, shortened by about 10 miles, in 22 years, 1880-1902. 

 wdiile during this same period. Brother John Glacier in northwest 

 Greenland lias been reportetd as advancing. Wegener (1930) found |j| 

 that during the last 35 years a considerable retirement had occurred | 

 along the fronts of the Disko and Northeast Bay outlet glaciers from 

 the inland ice, but small isolated glaciers, e. g., those of Nugsuak 

 Peninsula, had not changed materially. 



The topography of the land bordering the outer margin of the . 

 ice cap governs the general form, size, and rate of production of 

 icebergs. The inland ice. in some places, worms its way down to | 

 the coast through deep-carved fjords while in other sections it j 

 overflows all land features directly into the sea. The outward ex- , 

 pansion from the vast central reservoir results in marginal wastage, 

 ranging from melting by the sun and air to the calving of huge 

 masses, millions of tons in weight. Notwithstanding the great 

 length of the fragmenting periphery, we on the Marion expedition 

 w-ere struck by the relatively few definite iceberg producing points. 

 Quantitatively, it is estimated that 10 to 20 per cent of the solid 

 annual output from the ice cap is released as sizable icebergs. 

 Along the coast of west Greenland, for example, only 22 of the 

 100 and odd glaciers are known to be iceberg producing with one 

 group of these, 6 in number, accounting for 70 per cent of the j, 

 total annual output. As yet we know very little about the con- i 

 ditions that would transform a tidewater glacier wdth a small dis- I 

 charge into a point of great productivity, or vice versa. This is 

 not wholly a question of mass or of rate of motion, since the 'y 

 Ekip-Sermia Glacier we had the opportunity of visiting in the 

 Igclloluarsuit, Disko Bay, west Greenland, possessed both these quali- 

 fications, yet no sizable pieces of ice Avere calved. An important part 

 must be played by the ice fjords themselves, because some of the best 

 known iceberg producers are characterized b}- spacious, well-worn beds 

 that mold themselves smoothly into easy, outer embayments across the 

 coastal foreland. The boldly cut incisions along the western side of 

 Greenland l)etween the sixty-ninth and seventy-second parallels, the 

 heart of the iceberg country, provide deep-draft channels from which 

 the bergs have easy access to Davis Strait and to Bafhn Bay. The pro- 

 (hiction of icebergs we believe does not necessarily follow from the 

 presence of an ice cap even that the size of Greenland's; an essential 

 condition is topography of a sort providing favorable debouchment. 



In studying the degree and rate of iceberg productivity of tide- 

 water glaciers it is convenient to divide Greenland into six districts, 

 as follows : 



East. GiTonlaml Northeast Foreland te Caiie Faiewell. 



North Greenlaiid Indeiiendeiice Fjord to Cape Ah'xander. 



Wesleriunost Greenland Cajie Alexander to Cajie York. 



Melville Bay Cape York to Svarlenhuk Peninsida. 



Northeast and Disko Bays Svartenhuk I'eninsula to Kiredesniiiule. 



►South Greenland Eiiedesniinde to Cape Farewell. 



