GeoLog

Yosemite

Imaggeo on Mondays: Sunset and moonrise at Yosemite

Imaggeo on Mondays: Sunset and moonrise at Yosemite

This side view of Half Dome at Yosemite National Park (California, USA) was taken from Washburn Point, a less frequented overlook a few hundred meters away from the popular Glacier Point outlook. The sun just on the right side behind the camera, which gave the orange tint to the back side of Half Dome. At the same time a full moon was mere minutes from bursting in the background, which resulted in the warm glow of the horizon. A few stars have already started appearing on the clear sky and a few star trails are visible.

Description by Teamrat Ghezzehei, as it first appeared on imaggeo.egu.eu.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: The glacial landscape of Yosemite

 Glacial erratic rocks . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu)

Glacial erratic rocks . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu)

Yosemite National Park, in California, is renowned for its beautiful and striking landscapes. So much so, this is the second time it has feature on the blog this summer. While our last post on the park focused on the ancient volcanic history of its landscape, in this post we fast forward to the Plesitocene (some 110,000 to 12,000 years ago) to discover more about how glaciers shaped Yosemite’s landscape. Indeed, it is the glacier carved landscape which has made the park so famous!

During the last ice age, the high peaks and valleys of the Sierra Nevada (of which Yosemite belongs to) were covered by ice.  A vast continental ice sheet spread across much of the United States and Canada. Local climate variations as well as the geographical position of Yosemite meant that the accumulation of ice in the region was particularly unique, and didn’t belong to the vast continental ice sheet. Nevertheless, glaciers dominated the landscape during this time and the scars left behind by their presence resulted in a range of landforms observable today: including chatter marks (gouges left in granite by moving glaciers), glacier polish (shiny patches of granite), exfoliation (layered cracking of rocks which resembles onions peeling), and many others.

As glaciers move, they accumulate debris underneath their surface. As the vast frozen rivers advance, they carry the debris, which can range from pebble-sized rocks through to house-sized boulders, along with it. As the climate in the Yosemite region began to warm as the ice age came to an end, the glaciers slowly melted. Once all the ice was gone, the rocks and boulders, known as glacial erratics, were left behind.

One of the best examples of glacial erratics can be seen at Olmstead Point, near Mt. Hoffmann, in Yosemite National Park, as photographed by Yuval Sadeh. Yuval reminisces about the moment he reached the spot where the boulders are strewn across the landscape:

“I remember walking on this extremely smooth scraped surface, watching the glacial erratics rocks which looks like a giant artist placed them gently on the bedrock. Although the glacier melted many years ago, out there on the glacier carved surface it seems that time is standing still ever since.”

Imaggeo on Mondays: Half dome at sunset

Imaggeo on Mondays: Half dome at sunset

Yosemite’s Half Dome stands, majestic, over a granite dominated terrain in the Yosemite Valley area;  one of the most beautiful landscapes in northern America, and arguably, the world – it is also an Earth scientist’ playground.

Stamped into the west slope of the Sierra Nevada range, the Yosemite Valley is a collection of lush forests, deep valleys, meandering rivers and streams, all punctuated by huge domes and cliffs of ancient volcanic origin.

Come and explore this part of the world and you’ll not miss Half Dome. Standing at the head of the valley, the quartz monzonite (a coarse grained orthoclase and plagioclase feldspar dominated rock) structure rises a little short of 2700 m above sea level.

Despite standing proud in the present landscape, it was once a magma chamber, buried deep below a volcano. Over a long period of time, the molten magma cooled and crystalised to form the coarse granite rock we see today. Erosion and exposure did the rest, eventually exhuming the dome and cutting deep valleys into the surrounding landscapes.

For more information on the geology of the Yosemite Valley and Half Dome, please refer to these United States Geological Survey (USGS) resources:

The Geological Story of Yosemite Valley
How did Half Dome, acquire its unique shape?
Bedrock Geology of the Yosemite Valley Area

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.