Many died when the exploded and burned, others were blown into the river and picked up downriver floating on debris. The explosion was seen from Memphis. All the steamboats and those available on the river steamed to the scene.
The Sultana was a 1700 ton sidewheeler. Her hulk lay in the river for years. When the river fell, debris continued to spew forth, including skulls and other human remains.
Only one woman escaped, Anna Annis. Her military husband Lt. Harvey Annis, child, and sister went down with the boat.
There was some suspicion the explosion was caused by clinker coal grenades. The coal was stock piled on the dock and decks, exposed to those who might wish to cause problems. When shoveled into the fire boxes, the explosion might occur far from the origin of the contamination.
Robert Lowden was a possible suspect. I read that they found a letter after the war in which he confessed. Other rumors abounded too.
The "Greyhound" had gone down shortly before the "Sultana" with bombs in the coal supply
This has been in several sources: "Armchair Reader Civil War, Untold Tales of the Blue and Gray", another book entitled some thing like "The Civil War in St. Louis (which I think tells about the many fires along the water front)". As I recall the boats were docked in a several mile-long row. Once one of the wooden boats was ignited, the fire would spread from boat to boat (helped along with some highly flammable petroleum product). Some were cut loose and towed to the middle of the river to burn and sink. After several fires, the docking procedures were changed to spread the idle boats over more distance.