Sunday, 23 December 2012
Tsunami
For other uses, see Tsunami (disambiguation).
A tsunami (plural: tsunamis or tsunami; from Japanese: 津波, lit. "harbour wave";[1] English pronunciation: /suːˈnɑːmi/ soo-NAH-mee or /tsuːˈnɑːmi/ tsoo-NAH-mee[2]) is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.[3]
Tsunami waves do not resemble normal sea waves,
because their wavelength is far longer. Rather than appearing as a
breaking wave, a tsunami may instead initially resemble a rapidly rising
tide, and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train".[4]
Wave heights of tens of metres can be generated by large events.
Although the impact of tsunamis is limited to coastal areas, their
destructive power can be enormous and they can affect entire ocean
basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with over 230,000 people killed in 14 countries bordering the Indian Ocean.
The Greek historian Thucydides suggested in 426 BC that tsunamis were related to submarine earthquakes,[5][6] but the understanding of a tsunami's nature remained slim until the 20th century and much remains unknown[clarify].
Major areas of current research include trying to determine why some
large earthquakes do not generate tsunamis while other smaller ones do;
trying to accurately forecast the passage of tsunamis across the oceans;
and also to forecast how tsunami waves would interact with specific
shorelines.
Friday, 21 December 2012
Gunung Berapi
Gunung Berapi adalah bukaan, atau rekahan, pada permukaan atau kerak Bumi,
yang membenarkan gas, abu, dan batu cair yang panas bebas jauh di dalam
bawah permukaan bumi. Aktiviti gunung berapi membabitkan extrusion of rock yang cenderung membentuk gunung atau ciri-ciri berbentuk gunung melalui tempoh masa.
Gunung berapi biasanya terdapat di mana plak tetonik berpisah atau bertembung. Rabung tengah laut, seperti Rabung Tengah Atlantik (Mid-Atlantic Ridge), adalah contoh plak tetonik berpisah; Lingkaran Api Pasifik
pula mempunyai contoh gunung berapi yang terhasil akibat pertembungan
plak tetonik. Sebaliknya, gunung berapi biasanya tidak terhasil di mana
dua plak tetonik bergesel sesama sendiri. Gunung berapi juga boleh
terbentuk di kawasan di mana terdapat renggangan pada kerak Bumi dan di
mana kerak Bumi menjadi nipis (di kenali sebagai gunung berapi
antaraplat bukan titik panas), seperti di Lembah Rift Afrika (African Rift Valley), Rhine Graben Eropah dengan gunung berapi Eifelnya, Lapangan gunung berapi Wells Gray-Clearwater dan Rio Grande Rift di Amerika Utara.
Akhir sekali, gunung berapi boleh dihasilkan melalui pluma mantel (mantle plumes), yang dikenali sebagai titik panas; titik panas ini boleh berlaku jauh dari sempadan plak, seperti kepulauan Hawai. Amat menarik, gunung berapi titik panas juga didapati di tempat lain di sistem suria, terutamanya pada bulan dan planet berbatu.
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Gunung berapi:Ciri-ciri gunung berapi
Pemahaman paling biasa mengenai gunung berapi adalah gunung berbentuk
kon, menghambur lava dan gas beracun dari kawah gunung berapi
dipuncaknya. Gambaran ini hanya menggambarkan satu dari pelbagai jenis
gunung berapi, dan ciri-ciri gunung berapi adalah lebih sukar. Struktur
dan perangai gunung berapi bergantung kepada beberapa faktor. Sesetengah
gunung berapi mempunyai kemuncak bergerigih dibentuk oleh kubah lava
dan bukannya kawah puncak, sementara yang lain menunjukkan ciri-ciri
permukaan bumi seperti tanah tinggi rata yang besar. Lohong yang
mengeluarkan bahan gunung berapi (lava, iaitu magma yang keluar
kepermukaan, dan abu gunung berapi dan gas kebanyakannya wap dan gas
magma boleh didapati dimana-mana sahaja di kawasan tersebut. Kebanyakan
lohong ini menghasilkan kon lebih kecil seperti Pu'u 'Ō'ō di sisi gunung berapi Kīlauea, Hawai.
Gunung berapi jenis lain termasuk gunung berapi cryo (atau gunung berapi air batu), terutama di bulan bagi Jupiter, Saturn dan Neptune; dan gunung berapi lumpur,
yang pembentukannya kebanyakannya tidak berkait dengan aktiviti magma
yang diketahui. Aktiviti gunung berapi lumpur biasanya membabitkan suhu
yang jauh lebih rendah berbanding gunung berapi igneous, kecuali apabila gunung berapi lumpur sebenarnya merupakan lohon
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Berbeza dengan pāhoehoe, Aa adalah istilah berasal dari Polynesian, disebut Ah-ah, bagi aliran lava yang berceranggah, kasar |
Sunday, 9 December 2012
NASA-NOAA Satellite Reveals New Views of Earth at Night
NASA-NOAA Satellite Reveals New Views of Earth at Night
A global composite image, constructed using cloud-free night images from
a new NASA and National Oceanic and Atmospheric Administration (NOAA)
satellite, shows the glow of natural and human-built phenomena in
greater detail than ever before.
Many satellites are equipped to look at Earth during the day, when they
can observe our planet fully illuminated by the sun. With a new sensor
aboard the NASA-NOAA Suomi National Polar-orbiting Partnership (NPP)
satellite launched last year, scientists now can observe Earth's
atmosphere and surface during nighttime hours.
The new sensor, the day-night band of the Visible Infrared Imaging Radiometer Suite (VIIRS), is sensitive enough to detect the nocturnal glow produced by Earth's atmosphere and the light from a single ship in the sea. Satellites in the U.S. Defense Meteorological Satellite Program have been making observations with low-light sensors for 40 years. But the VIIRS day-night band can better detect and resolve Earth's night lights.
The new, higher resolution composite image of Earth at night was released at a news conference at the American Geophysical Union meeting in San Francisco. This and other VIIRS day-night band images are providing researchers with valuable data for a wide variety of previously unseen or poorly seen events.
"For all the reasons that we need to see Earth during the day, we also need to see Earth at night," said Steve Miller, a researcher at NOAA's Colorado State University Cooperative Institute for Research in the Atmosphere. "Unlike humans, the Earth never sleeps."
The day-night band observed Hurricane Sandy, illuminated by moonlight, making landfall over New Jersey on the evening of Oct. 29. Night images showed the widespread power outages that left millions in darkness in the wake of the storm. With its night view, VIIRS is able to detect a more complete view of storms and other weather conditions, such as fog, that are difficult to discern with infrared, or thermal, sensors. Night is also when many types of clouds begin to form.
The new sensor, the day-night band of the Visible Infrared Imaging Radiometer Suite (VIIRS), is sensitive enough to detect the nocturnal glow produced by Earth's atmosphere and the light from a single ship in the sea. Satellites in the U.S. Defense Meteorological Satellite Program have been making observations with low-light sensors for 40 years. But the VIIRS day-night band can better detect and resolve Earth's night lights.
The new, higher resolution composite image of Earth at night was released at a news conference at the American Geophysical Union meeting in San Francisco. This and other VIIRS day-night band images are providing researchers with valuable data for a wide variety of previously unseen or poorly seen events.
"For all the reasons that we need to see Earth during the day, we also need to see Earth at night," said Steve Miller, a researcher at NOAA's Colorado State University Cooperative Institute for Research in the Atmosphere. "Unlike humans, the Earth never sleeps."
The day-night band observed Hurricane Sandy, illuminated by moonlight, making landfall over New Jersey on the evening of Oct. 29. Night images showed the widespread power outages that left millions in darkness in the wake of the storm. With its night view, VIIRS is able to detect a more complete view of storms and other weather conditions, such as fog, that are difficult to discern with infrared, or thermal, sensors. Night is also when many types of clouds begin to form.
On Oct. 13, 2012, the Visible Infrared Imaging Radiometer Suite (VIIRS)
on the Suomi NPP satellite captured this nighttime view of the Nile
River Valley and Delta.
Credit: NASA Earth Observato
Credit: NASA Earth Observato
http://www.nasa.gov/mission_pages/NPP/news/earth-at-night.htmlry/Suomi NPP
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