In the above photo the green-brown waters of Barkol Lake sit within the pale shorelines of an ancient lake, hinting that the climate was once much wetter in this part of western China. Today the region is arid and brown. Barkol Lake’s annual mean precipitation is 210 millimeters (8 inches), while the annual evaporation rate is 2,250 millimeters (89 inches). The desert lake receives most of its water from runoff, and the water that remains after evaporation is very salty and full of minerals. Square ponds on the edge of the lake are probably evaporation ponds used to extract those minerals from the water.
Astronauts on the International Space Station snapped this photo on the lake on November 6, 2013. The astronauts were looking over the lake from the west, so east is toward the top of the photograph. The basin is closed, which means that the small streams in the photo run into the lake, but nothing runs out. Evaporation is the only means through which water leaves Lake Barkol.
The ancient shorelines show up as concentric rings, indicating that water levels have varied many times. One study identified five climates at Barkol Lake over the past 8,000 years, ranging from warm and wet to cold and wet and finally cold and dry. The average annual temperature in the area is now just 1° Celsius (34° F), though temperatures swing from extreme highs (33.5° C or 92.3° F) to extreme lows (-43.6° C or -46.5° F).
The two photos above show the before and after appearance of an area in Colorado that experienced a huge land slide.
On Sunday, May 25, 2014, a large mudslide rushed down a Colorado mountain near the town of Collbran covering an area three miles long and one-half to three-quarters of a mile wide. It claimed the lives of three ranchers and triggered a small earthquake.
The extent of the mudslide is evident in the top image, which was acquired by the Landsat 8 satellite on June 7. The lower image, taken by Landsat 8 on June 20, 2013, shows the slide region before the slide. The top edge of the slide, the scarp, is on the lower side of the image. The debris flowed north and ended at the toe, partially covering a natural gas well.
The slide happened in the Grand Mesa region of western Colorado, an area extremely prone to landslides. In fact, the recent mudslide began at the scarp of a previous landslide. The region is unstable because of its underlying geology. A layer of basalt lies on top of soft claystone that erodes easily. The basalt slumps when water erodes the soft rock beneath it, as illustrated in this diagram:
Landslides are most prevalent in this region during the spring and early summer when the ground is moist from snow melt and runoff.
On average, Colorado experiences thousands of landslides every year. According to the Colorado Landslide Inventory, most of the slides occur in the mountainous western half of the state.
To the human eye, the wind is invisible. It can only be visualized by proxy, by its expressions in other natural phenomena like blowing leaves, airborne dust, white-capped waters—or the patterns of clouds.
Cumulus cloud streets trace the direction, and sometimes the intensity, of winds. As puffy cumulus clouds form in the warmth of morning sunlight, they line up parallel to the direction of the wind. Often this means a straight line, as seen in the winter when cold winds blow over warmer waters, as shown in the NASA image below of the Great Lakes.
But clouds can also line up along the concentric, curved lines of high-pressure weather systems. The image above of Brazil was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on June 5, 2014. It shows a broad swath of the Amazon rain forest in Brazil and Bolivia as it appeared in the early afternoon (1:20 p.m. local time or 1720 Universal Time).
“Convective cloud streets form during the day due to heating of the land, often over fairly flat surfaces,“ wrote Patrick Minnis, a cloud researcher at NASA’s Langley Research Center. As sunlight warms the Amazon rain forest in the morning, water vapor rises on columns of heated air (thermals). When that humid air runs into a cooler, more stable air mass above, it condenses into fluffy cumulus clouds that can line up with the prevailing winds. “The clouds form in the morning and die out in the afternoon as the surface heating diminishes. They are very common over the United States during summer.
Kristopher Bedka, another Langley cloud researcher, examined a numerical weather prediction model to find the wind direction near the top of the boundary layer on June 5. “There appeared to be a high-pressure center in southeast Brazil causing the air flow to move counterclockwise around the center,” he noted. “The cloud streets aligned almost perfectly with the wind flow.”
No comments:
Post a Comment