To our east and right stretched the immense glaciers before mentioned, completely overrunning the route taken by Gunnlaugsson in 1835, and diverting the source of the Jökulsá, which rises in several arms from the extremity of the glacial tongue before mentioned. Upon our left and west lay the wide-spreading lava-desert of the Ódáðahraun.
Our way over the sandy bottom of the grand old watercourse was an easy one to travel, for the sand had absorbed sufficient water to make it firm and compact. Our attention was engaged for some time in watching the fanciful shapes that crowned the dark wall of ice upon our right, on the opposite side of the stream which now lay between us and the glacier; and now and then we could not help stopping to peer into some of the dark chasms which seemed to penetrate into the heart of the icy monster, and to admire the little cataracts of foam which spouted from clefts in the dark green ice, or to wonder at some icy pinnacle or turret, that ever and again tumbled from, perhaps, some few hundred feet above us with a roar and a splash into the river, there to be slowly melted, while the sound of its downfall echoed and re-echoed amongst the cavernous openings in the glacier from which it had fallen! After an hour or so we settled on a low sandy island in the middle of the river, which must have formed formidable rapids when the immense stream that had hollowed out this mighty watercourse had roared over its bed; but it was shallow enough now, and by judiciously picking our way it scarcely reached up to our knees as we waded to the little island. I here noticed, as I had often done before, an intermittent occurrence of waves in certain portions of the stream. These, in large rivers, are rather terrible things, but here they were on so small a scale as to make their examination simply a safe indulgence of harmless curiosity. These waves occur in all the sandy rivers, and they are occasioned by the sand and detritus, which is brought down by the river in large quantities, accumulating against some obstacle until such a time as it forms rapids, which increase in proportion to the durability of this suddenly-formed sandbank. In most cases it readily yields to the action of the water, and is carried away; if, however, the material which is thus piled up should be of a heavier character than usual, it soon accumulates to such an extent as to resist the action of the water altogether, and cause the current to alter its course. This shows how the rivers of Iceland may be diverted and changed from this cause alone, converting shallows into deep water, and deep water into shallows, indeed altering the position and character of the rivers altogether.