The tsunami that killed hundreds, possibly thousands of people after an earthquake in Indonesia on Friday was much bigger and more devastating than would normally be expected after that kind of quake, scientists say. "We expected it might cause a tsunami, just not one that big," geophysicist Jason Patton tells the New York Times. Tsunamis like the 18-foot monster wave that wrecked cities on Sulawesi island are usually caused by "megathrust" earthquakes that move land vertically, not "strike-slip" quakes like the 7.5-magnitude one Friday, which moved the earth horizontally, Patton says. The Sulawesi event was, however, localized, unlike the 2004 Indian Ocean tsunami.
It may have been the case, Patton says, that massive undersea landslides created the tsunami, or that the narrow bay that Palu sits at the end of concentrated the wave's power. Indonesian authorities have been strongly criticized for apparently canceling the tsunami alert too early, though expert Adam Switzer at the Earth Observatory of Singapore tells the AP that this is unfair. "What it shows is that the tsunami models we have now are too simplistic," he says. "They don't take into account multiple events, multiple quakes within a short period of time. They don't take into account submarine landslides." The official death toll now stands at 844, though authorities, who have been preparing mass graves, have been unable to access some hard-hit areas, the Guardian reports. (Read more tsunami stories.)