A new study by scientists at the University of California, Berkeley, has found that rockfalls in Yosemite National Park are triggered by heat from the sun. The study, published in the journal _Nature Geoscience_, is the first to identify heat as a major trigger of rockfalls in the park.

"We found that rockfalls are most likely to occur on hot days, when the sun heats up the surface of the rock and causes it to expand," said lead author Colin Stark. "This expansion creates stress in the rock, which can eventually cause it to fracture and fall."

The study found that rockfalls are most common in the summer months, when temperatures in Yosemite can reach over 100 degrees Fahrenheit. The researchers also found that rockfalls are more likely to occur in the afternoon, when the sun is at its strongest.

The study's findings have implications for rockfall risk management in Yosemite and other national parks. By identifying the conditions that trigger rockfalls, park managers can better predict when they are likely to occur and take steps to mitigate the risk to visitors.

"Our study provides new information that can help us to better manage the risk of rockfalls in Yosemite and other national parks," said Stark. "By understanding the conditions that trigger rockfalls, we can take steps to protect visitors and keep them safe."

Here are some of the key findings of the study:

- Rockfalls are most likely to occur on hot days, when the sun heats up the surface of the rock and causes it to expand.

- Rockfalls are most common in the summer months, when temperatures in Yosemite can reach over 100 degrees Fahrenheit.

- Rockfalls are more likely to occur in the afternoon, when the sun is at its strongest.

- The study's findings have implications for rockfall risk management in Yosemite and other national parks.