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.
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.
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.
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
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
Frequency of Occurrence of Earthquakes
Magnitude Average Annually
8 + 1¹
7 - 7.9 17 ²
6 - 6.9 134 ²
5 - 5.9 1319 ²
4 - 4.9
3 - 3.9
2 - 2.9
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:
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 & Climate
This view of Earth comes from NASA's Moderate
Resolution Imaging Spectroradiometer aboard the Terra
satellite. (Credit: NASA)
• Earth Science
• Natural Disasters
• Near-Earth Object Impacts
• Environmental Issues
• 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.