How much has the Grand Canyon changed over the last 100 years?

UA geosciences associate research scientist Robert Webb says a lot, and he has the pictures to prove it.

"People have had a heavy effect on what appears to be a very isolated place," Webb said.

While conducting his research, Webb was staggered when he discovered just how much influence there has been over the last 100 years.

Webb, author of Grand Canyon, a century of Change: Rephotography of the 1889-1890 Stanton Expedition, found photographs taken of the Grand Canyon in 1889 and decided to compare them to the landscape today.

"The project had a modest beginning but blossomed as I saw the potential of the photographs," Webb said.

His seven years of research involved spending 100 days on the Colorado River with UA research assistants and river guides. He said they searched for the exact locations where the historical photos were taken.

By comparing photos taken 100 years apart, around the same time of day, time of year and place, Webb traced the lives of individual plants and changes in plant distribution.

"One photo was even taken at the same minute one hundred years later," Webb said.

Webb also documented changes in the rapids, the effects of grazing and mapped debris flow that modified both sides of the canyons and rapids.

As Webb found out, some things never change.

A juniper snag (a dead tree) that appeared in one of the earlier photographs was still there 100 years later, and had been there since 1400 A.D., according to carbon-14 dating.

He also found 41 species of plants that had survived. In some areas, he was looking at the same individual plants as in the original pictures.

"Everywhere I looked, I found stability mixed with large amounts of human-caused change," Webb said. "There are parts of the canyon that are inaccessible to all but bighorn sheep and a few of the hardest hikers.

"There are isolated pockets that are relatively unchanged, but you would be surprised that tamarisk (a non-native plant that was absent from the earlier photos) is found in some amazingly remote places," he said.

In the final chapter of Webb's book he writes, "I remember standing in the National Archives holding one of Stanton's negatives and realizing ... I was holding history in my hands. I was also holding a powerful tool that can change our perception of the natural world."