Ashfall Fossil Beds
What happened at Ashfall?
The Ashfall deposit preserves the fossilized remains of ancient animals that perished in a dense volcanic ash fall which occurred during the late Miocene, approximately 12 million years ago.
Click below to see how the ash traveled and where it landed.
Before the Ash
Ashfall was an ancient water hole, a shallow depression where water would accumulate. The pond was used by many different species. “As far as we can tell, this was probably the only water hole for at least a mile in any direction,” explained paleo sleuth Mike Voorhies. It's likely that herds of animals from a fair distance away came to Ashfall at different times each day.
“Probably herds of zebra-like horses would come in and then maybe a bunch of camels later,” Voorhies said. “It's pretty likely that rhinos spent a fair amount of time actually basking in the waterhole. The fossil rhinos we have here have short legs like a hippo. It's pretty likely that these guys spent a fair amount of time wallowing and thrashing around in the water.”
Voorhies said that when the four-tusker elephants came to the water hole to drink and bathe, it’s probable that most other creatures left, since typically elephants are not very tolerant of other animals.
At night, the meat-eating animals would come to Ashfall to drink—saber cats and hyenas for example. There would be small creatures such as hedgehogs, too.
Ashfall Event Timeline
The ash cloud that descended on the water hole was not necessarily a visible cloud.
"The sky probably got dark," explained Voorhies. "It probably first was like a haze. It’d be like the air in L.A. You’d have a haze of material that came in, the sky would get darker and there’d be this stuff coming out of the sky. Since these animals had never seen snow this is probably something that was entirely new to them."
It appears birds such as cranes, hawks, and vultures died quickly, possibly within hours of when ash dust started falling. Their skeletons are found at the lowest levels of the ash beds, suggesting they were among the first to fall. Pond turtles were also among the early casualties.
The dust came down hard and fast. The animals with the least lung capacity perished by the herd as grey powder covered the land. The fossil layer containing the small deer, three-toed horses, and camels is higher than the remains of turtles and birds, suggesting the small animals survived a little longer. The ages of the animals and their states of preservation suggest they died in close succession.
Ash hung in the air and coated every bite of vegetation. Each step kicked up more ash, contributing to the slow death from suffocation. Skeletons of camels, horses, rhinos and other large animals show they had a lung condition known as Marie’s Disease. The animals were probably thirsty and suffering from high fever.
"After several weeks of inhaling the ash their body temperatures went way up and it probably felt good to them to lie down in the mud," Voorhies noted.
It’s unlikely that all the fossils in the ash bed were animals that just happened to be there at the time, Voorhies said. The sickened animals probably came because they knew they could get water there. Rhinos survived the longest, up to five weeks.
After all had died, the remains of the animals, small and large, were covered by the blowing, drifting ash. A few scavenging meat-eaters disturbed carcasses, but most bodies stayed in the same position in which they died. Some still had their last meals in their mouths or stomachs.
Ash remained in the air for years. Voorhies said, “The only thing that would make the ash stop blowing was when it fell into the water. The water would actually capture the ash and when you look at the fossil bed here at Ashfall, you can see that it consists of about 600 little separate layers of volcanic ash. Each one of those layers would be where a puff of wind had delivered a cloud of dust. It was captured by the water in the water hole. It fell to the bottom as a layer of ash mud."
Gradually, five to six feet of ash covered the bodies. "You could look any direction and there wouldn’t have been anything alive, probably for who knows, several years before eventually the place where the water hole used to be was completely destroyed by the ash fall," Voorhies explained.
Voorhies said plant life returned to Ashfall when a river went out of its banks and started depositing sand over the top of the ash bed. "Eventually, the same species of rhinos and camels and horses that had been destroyed by the ash moved back in and started eating the grass and shrubs that were growing here in the sand from the ancient river," he said. Mount St. Helens in Washington saw the return of deer and elk just ten years after its volcanic eruption in 1980. "The same thing happened at Ashfall," explained Voorhies. "We don’t have a good handle on how long that took, but as far as we know, nothing became extinct because of the ash fall."
12 Millon years later...
Though life resumed above the layers of volcanic ash, a remarkable process was underway beneath what eventually became Nebraska farmland.
The combination of quick burial, minerals leached from groundwater, and protection from disruptive forces produced some of the best-preserved fossils ever found.
Instead of one or two examples scattered across the countryside, Ashfall Fossils Beds yielded entire herds of specimens from a remarkable array of species, left in place, in order, and preserved in three-dimensional skeletons.
Thanks to the unusual events that took place 12 million years ago—and thanks to the care with which the site has been excavated—Ashfall offers paleontologists and park visitors a time capsule filled with examples of the animals and plants that lived in and near the water hole, providing a view of their life, climate, and world in amazing detail.
Explore some of the animals discovered at Ashfall in these high-resolution 3D models:
Lesson Plan - Ashfall Fossil Find
This is an inquiry activity that will introduce students to the variety of fossils that can be found at Ashfall Fossil Beds State Historical Park located north of Royal, Nebraska. Students will use what they have learned about describing fossils from previous activities to infer information, and identify cardstock representations of fossils to that of the real fossils found at Ashfall through research on the Ashfall website. Students will have four excavation opportunities to investigate and identify the animals at Ashfall. This activity takes 1-2 days to complete. This activity is an adaptation of the Great Fossil Find.