Low Lake Mead Water Levels Now Revealing Ancient Volcanic Eruptions

Lake Mead's receding water levels are now revealing ancient volcanic eruptions from millions of years ago.

Lake Mead is the biggest man-made reservoir in North America, formed by the Hoover Dam. Its water levels are rapidly evaporating due to the ongoing megadrought gripping the southwestern United States.

The lake, which lies across Nevada and Arizona, has made headlines in recent months due to the multitude of gruesome discoveries being made at its bottom, as the water continues to disappear. Multiple sets of human remains have been uncovered since May, and shipwrecks once concealed by the water are also emerging.

Scientists from the University of Nevada, Las Vegas have now discovered samples of ash within the lake from volcanoes that erupted millions of years ago.

According to a study published by the Geological Society of America, these samples were found in sedimentary rocks that haven't been seen since the Hoover Dam was first constructed in the 1930s. The ash comes from volcanoes that erupted in states as far away as as California, Wyoming and Idaho. According to a press release on the findings, these volcanoes erupted as long 12 million years ago.

Lake Mead
A file photo of Lake Mead and an artist's impression of an active volcano. The lake's receding waters are leading to a number of interesting discoveries. iStock / Getty Images

Scientists determined that the ash was from outside Nevada as nearby volcanoes would have been extinct at the time of the eruption. Scientists said in the study that volcanic eruptions can have a huge impact on environments far away from the source.

Most of the ash discovered is between 6 million and 12 million years old. Some is from more recent times, having been deposited 32,000 years ago.

According to the study, the health threats from these eruptions may still be ongoing in the area.

Eugene Smith, a UNLV emeritus professor of geology involved in the study, said in the press release that ash from even moderately explosive eruptions can travel hundreds of miles from the source.

"[This blankets] entire areas with anywhere from a centimeter to several meters of the heavy material," Smith said. "Although the Las Vegas Valley is currently very far away from any active volcanoes, we can and will have ash from these volcanoes fall over Southern Nevada in the future. Even a couple of millimeters of ash, when wet, is incredibly heavy and can take down power and telecommunications lines. It can block roadways. It is easily remobilized by wind and water. When inhaled, the incredibly tiny but sharp glass grains in the ash can cause significant, chronic lung conditions such as silicosis."

There are four possible sources for the ash, identified by scientists. They include the Snake River Plain-Yellowstone hotspot track, which has been active for 15 million years, and the volcanoes of Walker Lake, which is known for producing huge earthquakes across Nevada and California in 2019 and 2020.

"Studying the past can help you plan for the future," Lab manager at the UNLV College of Sciences' Cryptotephra Laboratory for Archaeological and Geological Research, Racheal Johnsen, said in the press release. "The ash layers we study come from volcanoes long extinct. However, studying them has helped us determine just how often the Las Vegas area was inundated with ash over time and may help us prepare for future events from active volcanoes far from us."