What causes lightning?

Lightning is produced in thunderstorms when liquid and ice particles above the freezing level collide, and build up large electrical fields in the clouds. Once these electric fields become large enough, a giant "spark" occurs between them, like static electricity, reducing the charge separation. The lightning spark can occur between clouds, between the cloud and air, or between the cloud and ground. As in the photo above, cloud-to-ground lightning usually occurs near the boundary between the updraft region (where the darkest) clouds are, and the downdraft/raining region (with the lighter, fuzzy appearance). Sometimes, however, the lightning bolt can come out of the side of the storm, and strike a location miles away, seemingly coming out of the clear blue sky. As long as a thunderstorm continues to produce lightning, you know that the storm still has active updrafts and is still producing precipitation. The temperature inside a lightning bolt can reach 50,000 degrees F, hotter than the surface of the sun. Objects that are struck by lightning can catch on fire, or show little or no evidence of burning at all.

Are glaciers disappearing?7. The Matterhorn

c. 1960 & today, Getty Images Many often wonder why Europeans get so hot and bothered about climate change. Perhaps it has something to do with the fact that they are in direct, daily contact with one very sobering reality — their ice is vanishing.  European glaciers have been some of the hardest hit by climate change. Since the first half of the 19th century, about two-thirds of the ice cover was lost in the Pyrenees with a marked acceleration after 1980 (Chueca et al. 2005 via: UNEP) and in the Alps, home to the world famous Matterhorn, nearly half the glaciers have disappeared since record keeping began. Often called the "water tower" of Europe, the Alps contain 40 percent of Europe's fresh water supply. The dramatic disappearance of ice on the Matterhorn last year has prompted the need for the border between Switzerland and Italy to be redrawn.  6. Alaska

Muir Glacier, 1941 

Muir Glacier, 2004 It's always struck me as a bit ironic that Alaska, home to several of the most famous gubernatorial climate skeptics (including Sarah Palin) is also home to some of the most dramatic examples of climate change. The astonishing recession of the massive Muir glacier is just one example among dozens (see graphs below), causing many scientists to warn of earthquakes triggered by tectonic plates with suddenly lightened loads.  5. Himalayas

NASA Home to the planet's largest body of ice outside the polar caps, the Himalayas feed several of the world’s largest rivers, supporting close to a billion people. In the western region of Himachal Pradesh, new evidence tracks an annual ice loss of nearly 3 feet in thickness per year, doubling in the past decade from the decade prior (Berthier et al, 2007). 

Will the Himalayan glaciers disappear this century? Not likely, but Chinese government officials are growing concerned that retreating ice may spell the end of reliable water supplies for China. 4. Greenland

Helheim Glacier, Spring 2001 

Helheim Glacier, Spring 2005 Satellite images of Greenland’s Helheim Glacier dating back to the 50s shows that this massive glacier has remained in tact for decades. But In 2000 it suddenly began disappearing. By 2005 the glacier had retreated a total of 4 1/2 miles — at an average rate of 110 feet per day. Ironically, retreating glaciers in Greenland have enabled dozens of new oil and gas exploration projects as vanishing ice makes room for heavy drilling equipment. 

3. Mount Kilimanjaro

Mount Kilimanjaro, February 1993 & February 2000 Last week a band of celebrities hiked up Mount Kilimanjaro to raise awareness for the African water crisis. The famous snow-cap formed 11,000 years ago but has diminished more than 85 percent since 1912, and nearby Mount Kenya has lost nearly ALL of its ice at an average of 1 meter per year, threatening water supplies for millions of people. Scientists now predict that the last great African glaciers could be gone within 20 years.  2. The Andes

Dr. Edson Ramirez/AP; Universidad Mayor de San Andres The Chacaltaya glacier, once the highest ski resorts on earth, has completely vanished in the relative blink of an eye. A study on Bolivian glaciers in 1998 predicted the glacier’s disappearance by the year 2015, a claim that at the time was dismissed as overly dramatic. But early last year, it was officially announced that the glacier ”... no longer exists,” an event which threatens both water and power supplies in the Andean region. 

Melting has tripled in the last decade, and it is expected that several adjoining clusters could have less than 30 years to survive. 1. Glacier National Monument

Glacial National Park — 1938 & 2005 

Based on the latest reports, Montana may have to think of a new name for its famous Glacier National Monument. Of the 38 square-mile area once covered by glaciers, less than 25 percent remains. Researchers believe that by the year 2030, the vast majority of ice in Glacier National Park will be gone unless current climate patterns are reversed. ADDENDUM: The GRID Report (PDF) has just released new data for its upcoming 2007/2008 report which shows ever-increasing rates of deglaciation. It's filled with dozens of almost incomprehensible graphs like this one which shows that of the 16 major glaciers studied, all 16 are rapidly melting: For a primer on basic glacier science click on Part 1 of this post.To learn more about the IPCC Glacier Goof-up read the oh-so-controversial post. MNN homepage photo: repistu/iStockphoto 

 

Is the number of earthquakes increasing?

With the recent earthquakes in Haiti, Chile and Turkey, many people are asking if the number of earthquakes is increasing.

How Often Do Earthquakes Occur?Worldwide, strong earthquakes happen more than once per month. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day. To create a mountain system might take several million medium sized earthquakes over tens of millions of years.

The USGS provides a nice summary of historical earthquake activity. Go to

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

Frequency of Occurrence of Earthquakes

Magnitude Average Annually 8 + 1 ¹7 - 7.9 17 ² 6 - 6.9 134 ² 5 - 5.9 1319 ²

4 - 4.9 13,000(estimated)

3 - 3.9 130,000(estimated)

2 - 2.9 1,300,000(estimated)

¹ Based on observations since 1900. ² Based on observations since 1990.

Dr. Michael Blanpied, from the USGS Earthquake Hazards Program, answered questions from the public about the causes of recent earthquakes. Read The Washington Post article:Seismic Science:http://www.washingtonpost.com/wp-dyn/content/discussion/2010/03/08/DI2010030802570.html

Chilean Quake May Have Shortened Earth Days

The Feb. 27 magnitude 8.8 earthquakes in Chile may have shortened the length of each Earth day. Science Daily (Mar. 2, 2010)

Earth & ClimateThis view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite. (Credit: NASA)

See Also:← Earthquakes ← Earth Science ← Natural Disasters ← Geology ← Near-Earth Object Impacts ← Environmental Issues

Reference← Earthquake liquefaction ← Elastic-rebound theory of earthquakes ← North Anatolian Fault ← Great Chilean Earthquake

JPL research scientist Richard Gross computed how Earth's rotation should have changed as a result of the Feb. 27 quake. Using a complex model, he and fellow scientists came up with a preliminary calculation that the quake should have shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second).

Perhaps more impressive is how much the quake shifted Earth's axis. Gross calculates the quake should have moved Earth's figure axis (the axis about which Earth's mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth's figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).

By comparison, Gross said the same model estimated the 2004 magnitude 9.1 Sumatran earthquake should have shortened the length of day by 6.8 microseconds and shifted Earth's axis by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).

Gross said that even though the Chilean earthquake is much smaller than the Sumatran quake, it is predicted to have changed the position of the figure axis by a bit more for two reasons. First, unlike the 2004 Sumatran earthquake, which was located near the equator, the 2010 Chilean earthquake was located in Earth's mid-latitudes, which makes it more effective in shifting Earth's figure axis. Second, the fault responsible for the 2010 Chiliean earthquake dips into Earth at a slightly steeper angle than does the fault responsible for the 2004 Sumatran earthquake. This makes the Chile fault more effective in moving Earth's mass vertically and hence more effective in shifting Earth's figure axis.

Gross said the Chile predictions will likely change as data on the quake are further refined.