The Sierra Nevada Files

A recent paper on the historic 22-year drought in the Southwest U.S., published in Nature Climate Change by Williams and colleagues, received a great deal of attention in the media. Even though it is not focused on the Sierra Nevada, it used data from the Sierra Nevada and also has important ramifications for the range; therefore, I thought it was appropriate to discuss it here. In addition, this blog provides the opportunity to present interesting and important details that may have been left out in the press accounts. The yellow box on this map outlines the study area. This map also shows the vapor pressure deficit (VPD) anomaly, a measure of how 'thirsty' the air has been during the past twenty years relative to previous years. This anomalously high vapor pressure deficit is thought to be responsible for the outbreak of large fires in the region.  One of the many strengths of this paper is that it focuses on soil moisture, rather than temperature or precipitation. Soil mois

One of the most striking features in the Sierra Nevada is a sinuous set of flat-topped ridges in the Stanislaus River watershed. About 28 km (18 miles) long, these mesas rise above a generally flat and featureless plain.   Table Mountain in the Stanislaus River watershed. Table Mountain starting from the upper-left corner of the image, passing by New Melones Reservoir, and ending at the bottom-right corner. The peculiar shape of these ridges is due to their geologic origin. About 10 million years ago, lava erupted from a vent near the crest of the Sierra Nevada and poured down a river bed. As the lava cooled, it assumed the shape of the river. Over time, the material surrounding the hardened lava eroded away, leaving behind the imprint of the river. A report by J.D. Whitney, published in 1865, was the first to describe the formation of Table Mountain. In this report, Whitney included a cross-section of Table Mountain, at the Buckeye Tunnel Mine, that has since been reproduced in numero

 As anyone living in the Golden State knows, California has been suffering through an unprecedented increase in fires, many of them burning through forests in the Sierra Nevada. Incredibly, as noted in a recent paper by Hiraga and Kavvas in the journal Fire , more than 7% of the land surface in California burned in 2017 - 2020. These fires have resulted in hundreds of deaths, the destruction of tens of thousands of structures, and severe financial losses. Sparked by lightning, the North Complex Fire in the northern Sierra Nevada destroyed 2500 buildings and led to 16 fatalities. At 320,000 acres, it was the 6th largest fire in California history and the deadliest fire in 2020. Photo credit: Brian Bahouth, https://www.sierranevadaally.org/ Understanding the precise meteorological and hydrological conditions that lead to wildfires in California is important for a variety of reasons. First, this information can help in mitigating ignition sources. Some of the worst wildfires have been tr

It's easy enough to see rocks at the Earth's surface but how do geologists figure out what types of rocks are deep below - even hundreds of kilometers beneath the surface? This is an important question because critical geological processes, such as plate tectonics, happen deep within the crust (the upper layer of the Earth) and within the mantle (the layer beneath the crust). The main technique for examining Earth's architecture is called seismic tomography,  a method whereby seismic waves are used to probe the Earth's interior. At the most basic level, seismic waves travel slowly through warm and bouyant material but quickly through cold and dense material; therefore, by measuring the speed of these waves as they travel through Earth's interior, we can get important information about what's down there that would be, otherwise, impossible to obtain. Example of seismic wave velocities in the south Pacific. Blue indicates high velocities and red indicates low velo

Mountainous landscapes, because of their deep valleys and tall peaks, support a wide variety of microclimates. These microclimates, in turn, provide homes for a diverse assortment of plants and animals. A study by Daniel Cayan and his colleagues, published by the Parks Stewardship Forum, investigated the phenomenon of cold air pools  in Devils Postpile National Monument, just north of Mammoth Mountain. Location of Devils Postpile National Monument (red dot on map). From Figure 1 of Cayan et al. Google Earth Image of the study area. The center of the image is a deep valley that supports pools of cold air. This region is in the headwaters of the San Joaquin River. Cold air pools are localized areas of cold air that develop along valley bottoms, typically at night. Because these are persistent features, they can serve as refuges for plants and animals as they slowly adapt to a warming climate. Given the potential importance of cold air pools to ecosystems, Cayan and his colleagues analyze

Lakes can accumulate sediments and protect them from disturbance for thousands of years, making them excellent repositories of environmental information. Samples of lake sediment retrieved during coring expeditions can be analyzed to reconstruct critical characteristics of past environments, such as local vegetation communities, fire frequency, and temperature. Illustration of a coring rig installed on a raft. The casing (essentially an empty tube) is pushed into the sediment. Credit: http://www.museum.state.il.us/muslink/behind/htmls/cr_bot_pal3.html Coring lake sediment. This is an example of a sediment core. Different layers, often associated with seasonal changes, can be seen in the sediment. Photo credit: Jamie Howarth To investigate whether changes associated with global warming could be detected in sediment that has accumulated in lakes in the Sierra Nevada, Laura Streib and her colleagues collected sediment from June Lake, which is in the eastern Sierras and about 20 km south o