question:  What could be meant by the Schwartzberg quote in the passage saying that, "It looks like sand dancing in a child's sieve."?
context: It has happened a hundred times in the long history of Earth—and, sooner or later, will happen again! Not even in the Rockies could anyone remember a series of rock slides as bad as this. Newspapers in the mountain states gave it a few inches on the front page; anything is news in late August. Only Joseph Schwartzberg, head geographer of the Department of the Interior, wondered if the disturbance might not be a settling of the Kiowa Fault. The idea was not nearly so exciting as a volcano, even a lava-less one, and you couldn't draw a very dramatic picture of it. The dust volcano was on the face of it a more plausible theory. They found themselves on the scene of what was fast becoming the most violent and widespread earthquake North America—probably the world—has ever seen in historic times. To describe it in the simplest terms, land east of the Fault was settling, and at a precipitous rate. East, where sharp reports and muffled wheezes told of continued buckling and dropping, the earth trembled downward. Atop the new cliffs, which seemed to grow by sudden inches from heaving rubble, dry earth fissured and trembled, sliding acres at a time to fall, smoking, into the bucking, heaving bottom of the depression. Dry earth churned like mud, and rock shards weighing tons bumped and rolled about like pebbles as they shivered and cracked into pebbles themselves. "It looks like sand dancing in a child's sieve," said the normally impassive Schwartzberg in a nationwide broadcast from the scene of disaster. Land west of the Fault was holding firm, though Denver had recorded several small tremors; everywhere east of the Fault, to almost twenty miles away, the now-familiar lurch and steady fall had already sent several thousand Coloradans scurrying for safety. All mountain climbing was prohibited on the Eastern Slope because of the danger of rock slides from minor quakes. Just below Masters, Colorado, the river leaped 70-foot cliffs to add to the heaving chaos below.
output:  The swirling dust and rocks were churning substantially.
options:  The rocks and dust were quickly mixing with water and creating mud.  The rocks and dust were disappearing.  The swirling dust and rocks were churning substantially.  He was comparing the dust and rocks to a child by their minimal presence.