Yosemite Valley is a breathtaking natural wonder, but it also presents a unique geological challenge: rockfalls. These events occur frequently, with massive boulders, sometimes larger than cars or even apartment buildings, tumbling down the steep cliffs every few days. To study and monitor these rockfalls, geomorphologist Greg Stock collaborates with USGS engineer Brian Collins. They employ advanced technologies such as high-resolution photography, LiDAR, aerial surveillance, and 3D modeling to keep track of these occurrences, which is vital given the park’s annual influx of five million visitors.
Yosemite’s towering cliffs make it particularly susceptible to rockfalls. A notable incident in 1996 saw a colossal rock plummet nearly 3,000 feet to the valley floor, creating winds strong enough to topple over a thousand trees in mere seconds. But what causes these rocks to break free from the cliffs?
Greg explains that while the final trigger for a rockfall might be sudden, the preparation can span decades or even centuries. Factors such as roots growing into cracks and water freezing within them can contribute to the eventual fall. Interestingly, about a third of Yosemite’s rockfalls occur without any identifiable trigger. Historically, only witnessed rockfalls were recorded, but Greg and Brian’s use of modern tools allows them to study and learn from events that might otherwise go unnoticed.
Brian describes one of their key tools: ground-based laser scanning, also known as terrestrial LiDAR. This technology generates millions of data points to create detailed 3D models of the cliffs. High-resolution photography is also used to closely examine the rock faces and identify areas of recent activity. By analyzing these data, Greg and Brian can pinpoint hazard zones where rockfalls have previously occurred, suggesting these areas are likely to experience future events.
Greg finds it fascinating to see a newly fallen boulder next to one that might be a thousand years old, highlighting the ongoing nature of these geological processes. Brian agrees, noting that the patterns of rockfalls remain consistent over time. However, predicting the exact timing of a rockfall remains a challenge, as various factors like weather changes, earthquakes, and wildlife can influence the stability of rock cracks.
To better understand these triggers, Greg and Brian have installed specialized equipment called crackmeters to measure the movement of cracks over time. Their research over three and a half years revealed that cracks tend to shift daily during warm periods. This finding supports a hypothesis among rock climbers and geologists that hot weather could trigger rockfalls.
Greg notes that while they have identified heat as a probable trigger, further research is needed to determine whether the temperature on a specific day or the change in temperature from the previous day is more significant. Despite these uncertainties, their work is highly regarded by scientists studying similar phenomena in places like Switzerland and Brazil.
Greg and Brian’s research has uncovered deposits much larger than any observed in the last 150 years, indicating the potential for significantly larger rockfalls in the future. This underscores the importance of their work in ensuring the safety of millions of visitors to Yosemite each year.
Greg emphasizes that while visitors might assume the cliffs have remained unchanged for thousands of years, they are, in fact, constantly evolving due to rockfalls. This ongoing research is crucial for understanding and mitigating the risks associated with these natural events.
This episode was presented by the US Air Force. For more episodes of Science in the Extremes, be sure to check out the series and subscribe for more fascinating insights into the natural world.
Engage in a hands-on workshop where you will simulate rockfalls using scaled models of Yosemite’s cliffs. Use materials like sand, gravel, and clay to recreate the geological processes discussed in the article. Analyze the impact of different variables such as water infiltration and temperature changes on rock stability.
Participate in a computer lab session where you will work with real LiDAR data to create 3D models of Yosemite’s cliffs. Learn how to identify potential hazard zones and understand the significance of these models in predicting rockfalls. Discuss the limitations and challenges of using technology in geological studies.
Join a field trip to a local geological site where you can observe rock formations and potential rockfall areas. Apply the concepts learned from the article by identifying signs of rock instability and discussing possible triggers. Document your observations and present your findings to the group.
Prepare a presentation on the research methods used by Greg Stock and Brian Collins. Focus on the effectiveness and challenges of their techniques. Engage in a debate with your peers on the ethical implications of human intervention in natural processes and the balance between safety and conservation.
Participate in an interactive seminar where you will explore various triggers of rockfalls, such as temperature changes and seismic activity. Use case studies from Yosemite and other locations to analyze different scenarios. Collaborate with your peers to develop a risk assessment plan for a hypothetical rockfall event.
Here’s a sanitized version of the provided YouTube transcript:
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In Yosemite Valley, rockfalls can occur every 4-5 days, with boulders larger than an average car or apartment building tumbling down steep mountainsides. Greg Stock, a geomorphologist, collaborates with USGS engineer Brian Collins. They utilize high-resolution photography, LiDAR, aerial surveillance, and 3D modeling to monitor rockfalls in the park, which is crucial given the five million visitors that come to Yosemite each year.
GREG: Yosemite is particularly prone to rockfalls due to its massive cliffs. For instance, in 1996, a large rock fell nearly 3,000 feet to the valley floor, generating hurricane-strength winds that knocked over a thousand trees in seconds.
What triggers a rock to fall from the cliff? GREG: There are likely decades or even centuries of preparation before a rock falls, but the final trigger is what causes it to break free. Roots can grow into cracks and expand, pushing rocks off, and water freezing in these cracks can also contribute. However, about a third of the rockfalls in Yosemite occur without an identifiable trigger. Historically, rockfalls were only recorded if witnessed by humans, so Greg and Brian use various tools to track and learn from events that may happen unnoticed.
BRIAN: One of our tools is ground-based laser scanning, also known as terrestrial LiDAR. This technology provides millions of data points to create a 3D model of the cliff. We also use high-resolution photography to closely examine different aspects of the wall and identify recently active rockfall areas. Additionally, Greg and Brian pinpoint hazard zones where previous rockfalls have occurred. Their computer models indicate these areas are likely to experience future rockfalls.
GREG: It’s fascinating to see a new boulder from six months ago next to one that is probably a thousand years old or more.
BRIAN: Yes, the same patterns are evident.
GREG: The past informs the present.
BRIAN: Exactly. While the team can identify unstable areas, predicting when a rockfall will occur remains challenging. Weather variations, earthquakes, and wildlife can influence whether a crack remains stable for a century or leads to a significant rockfall event.
BRIAN: We installed specialized equipment called crackmeters behind the cracks to measure how much they open over time. Over three and a half years, we observed that during warm periods, the cracks would shift daily.
Greg and Brian’s research confirmed a hypothesis among rock climbers and geologists: that hot weather could trigger rockfalls.
GREG: We’ve identified heat as a probable trigger, but we still need to determine whether the temperature on a specific day or the temperature change from the previous day is more significant.
Despite these uncertainties, Greg and Brian’s research is highly regarded by scientists studying mountains in Switzerland and Brazil. Their unique opportunity to gather extensive data on rockfalls in Yosemite reveals that there are deposits much larger than anything observed in the last 150 years, indicating the potential for significantly larger rockfalls in the future. This underscores the importance of their work in keeping millions of Yosemite visitors safe each year.
GREG: Visitors often look at these cliffs and assume they have remained unchanged for thousands of years, but that’s not the case. The cliffs are constantly evolving due to rockfalls.
This episode was presented by the US Air Force. Learn more at airforce.com. For more episodes of Science in the Extremes, check out this one right here. Don’t forget to subscribe and return to Seeker for more episodes. Thank you for watching.
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This version removes informal language and exclamations while maintaining the informative content of the original transcript.
Rockfalls – The rapid downward movement of rock fragments or boulders from a steep slope or cliff. – Example sentence: The team installed sensors to study the frequency and impact of rockfalls in the mountainous region.
Geology – The scientific study of the Earth, including its composition, structure, processes, and history. – Example sentence: Her geology research focused on the mineral composition of volcanic rocks.
Monitoring – The systematic observation and recording of changes or conditions in a specific environment over time. – Example sentence: Continuous monitoring of seismic activity is crucial for predicting potential earthquakes.
Cliffs – Steep rock faces or slopes, often found at the edge of the sea, a river, or a mountain. – Example sentence: The erosion of the coastal cliffs has been accelerated by rising sea levels.
Boulders – Large rocks, typically greater than 256 millimeters in diameter, that have been transported and deposited by natural processes. – Example sentence: The presence of boulders in the valley indicates a history of glacial activity.
Temperature – A measure of the warmth or coldness of an environment or substance, often influencing geological processes. – Example sentence: The temperature fluctuations in the desert can cause significant weathering of exposed rock surfaces.
Research – The systematic investigation and study of materials and sources to establish facts and reach new conclusions. – Example sentence: Her research on sedimentary layers provided new insights into the region’s geological history.
Hazards – Natural or human-induced processes that pose a threat to life, property, or the environment. – Example sentence: Identifying geological hazards is essential for developing effective risk management strategies.
Geomorphology – The scientific study of landforms and the processes that shape them. – Example sentence: Geomorphology helps scientists understand the evolution of landscapes over geological time scales.
Stability – The condition of being resistant to change or displacement, often used in reference to slopes or structures. – Example sentence: Engineers assessed the stability of the hillside before constructing the new highway.
