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More information from NOAA on volcanoes...
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Volcanoes
The word volcano comes from the island of Vulcano in the Mediterranean Sea. Long ago people thought this island mountain was the chimney of the blacksmith forge of the Roman God Vulcan. The steam and ash that came out of the vent was a sign that Vulcan was working at his forge making weapons for Jupiter and Mars. In Hawaii and other Polynesian islands, local people once attributed volcanic eruptions to the Goddess Pele. They believed Pele was moving from island to island as she sought to escape her evil sister, Na Maka O Kaha'i, the goddess of the sea. Today, scientists understand that volcanic eruptions are surface reminders of Earth's still hot interior.
The ash cloud formed by the May 18, 1980, eruption at Mount Saint Helens, WA. More images...
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Sixty percent of all active volcanoes are found at crustal plate boundaries such as the Pacific Plate. Earth's crust, like the cracked shell of a hard-boiled egg, is broken into a number of "plates". These floating pieces of crust are moving about very slowly on the hotter interior. Where the plates are moving apart or colliding with one another, volcanoes may form. Volcanoes also form oceanic islands in the Pacific Ocean or Mediterranean Sea where "hot spots" occur in the crust and mantle.
Many kinds of volcanic activity can endanger the lives of people and property. Most of the activity involves the explosive ejection or flowage of rock fragments and molten rock. Volcanoes that erupt explosively can send particles as far as 20 miles high and many miles away from the volcano. The volcanic ash from these types of eruptions is a significant hazard to aviation. If an airplane flies into a volcanic cloud, it can lead to engine damage and malfunction and to many other kinds of aircraft damage. Volcanic eruptions near coastlines can generate damaging tsunami waves that can cause death and destruction among coastal communities.
To ensure safe navigation and monitor possible climatic impact, NOAA records global historic volcanic eruptions, tracks volcanic ash eruptions affecting the United States, issues volcanic ash advisories and provides ash cloud forecasts. For more information on volcanoes, visit NOAA's Volcano website.
Recent Volcano Observatory Activity Reports from USGS
Cleveland Status Report issued Jul 23, 2008 11:28 ADT Volcano Alert Level WATCH - Aviation Color Code ORANGE
Thick clouds have obscured satellite views of Cleveland for the last 10 hours. No plumes have been visible in satellite data since 16:00 AKDT yesterday (midnight UTC). Satellite data from early yesterday evening continue to show strong thermal anomalies near Cleveland's summit. These data strongly suggest the presence of lava at Cleveland. Details...
Okmok Status Report issued Jul 23, 2008 11:28 ADT Volcano Alert Level WATCH - Aviation Color Code ORANGE
The eruption of Okmok Volcano continues. The character of seismicity has changed in the last 12 hours from episodic, high-amplitude pulses to nearly continuous, mid-level volcanic tremor. Recent satellite data continue to show older plumes drifting away from Okmok toward the E/SE. Weather clouds have prevented unobscured views of the volcano over the last 10 hours.
Stronger explosive activity could resume at any time with little or no warning. Details...
HAWAIIAN VOLCANO OBSERVATORY DAILY UPDATE issued Jul 23, 2008 08:19 HST Volcano Alert Level WATCH - Aviation Color Code ORANGE
This report on the status of Kilauea volcanic activity, in addition to maps, photos, and webcam images (available using the menu bar above), was prepared by the USGS Hawaiian Volcano Observatory (HVO). Hawai`i Volcanoes National Park status can be found at http://www.nps.gov/havo/ or 985-6000. Hawai`i County Viewing Area status can be found at http://www.lavainfo.us or 961-8093.
Activity Summary for last 24 hours: Kilauea summit continued to contract. Small amounts of ash and elevated amounts of sulfur dioxide gas continued to issue from the Halema`uma`u vent. At the east rift eruption site, Pu`u `O`o cone is slowly contracting and incandescence bursts were observed from vents on the crater floor; lava flows from the TEB vent through tubes to the ocean at Waikupanaha.
Last 24 hours at Kilauea summit: For most of the night, views of incandescence were blocked by fog and rain. Blowing and rock clatter sounds were heard at the vent this morning. An explosion-like seismic signal was recorded at 06:41 H.s.t.
A white plume rising from the Halema`uma`u vent is totally hidden from view by fog this morning. The SO2 emission rate remained high and variable; the most recent average measurement was 1,300 tonnes/day on July 21 compared to an average of 500 tonnes/day on July 18 and a pre-2008 background rate between 150-200 tonnes/day.
A small amount of ash is still carried by the plume. The current strong winds are contaminating the samples with windblown debris but plume-derived material is still evident.
The summit tiltmeter network recorded rainfall-induced signal starting around 1 pm masking any earth tilting signals. GPS receivers on opposite sides of the summit caldera continued to record contraction centered in the southeastern caldera.
Seismic tremor levels were at elevated values and continued to increase slowly. The number of RB2S2BL earthquakes beneath Halema`uma`u Crater remain at background values of about 20-40/d. Two earthquakes were located on south flank faults.
Last 24 hours at the middle east rift zone vents and flow field: Magma continued to degas through Pu`u `O`o Crater resulting in an unusually high emission of 7,100 tonnes/day of sulfur dioxide on July 18, up from 6,300 tonnes/day on July 17 and background values of about 2,000 tonnes/day. Overnight, the webcam recorded bursts of incandescence from vents on the crater floor on the right side of camera center.
The tiltmeter on the north side of Pu`u `O`o cone recorded minor oscillations with rainfall-induced tilt changes masking any cone tilting. GPS receivers recorded weak contraction across the crater.
Lava enters the tube system under the TEB vent and flows beneath the rootless shield complex through tubes to the ocean. Overnight, no incandescence was noted in the area from the rift zone to the top of the pali above the abandoned Royal Gardens subdivision. CD officials reported lingering surface flow activity on the pali and several changes at the ocean entry last night - no more explosions or lightning in the steam plume, spread of the ocean entry from a single to at least three entry points, good views of a surface flow over a black sand beach, and an apparent bench collapse (possibly around 10:10 am on July 22 based on seismic records) restored a direct entry view from the County Viewing Area.
Definitions of terms used in the update:
GOES-WEST satellite: a NOAA satellite used most often for weather tracking. The loop http://www.ssd.noaa.gov/VAAC/kilauea/sloop-vis.html is posted by the Washington DC Volcanic Ash Advisory Center for the purpose of tracking emissions from Hawai`i volcanoes. The imagery automatically switches from infrared at night to visual during the day. Recently, it has been useful for tracking volcanic gas emissions from Halema`uma`u, Pu`u `O`o, and the Waikupanaha ocean entry during the day and hot lava flows at night.
Volcano Watch: weekly newspaper-like article written by HVO scientists on a volcano topic of interest. These articles are usually printed in the Sunday editions of the Hawai`i Island newspapers Hawaii Tribune Herald and West Hawaii Today. More than 800 of these articles have been written and are archived on the HVO website (menu at the bottom of the homepage hvo.wr.usgs.gov).
VLP seismic tremor: seismic tremor is continuous ground vibrations simultaneously at many different frequencies. VLP is a very long period or very low frequency component which, at the Halema`uma`u vent, has a period of 20-30 seconds or a frequency of 0.03-0.05 cycles per second (Hertz or Hz).
RB2S2BL earthquakes: earthquakes that were recorded but too small to be located. These quakes have magnitudes less than 1.7 and may only be recorded on one or two seismometers. Recording at a minimum of 4 seismometer sites is required to locate an earthquake.
wink: an abrupt shutting off of incandescence at a vent lasting for several minutes. At the Halema`uma`u vent, winks usually start with or immediately follow a small, local earthquake. The diminishment of incandescence is due to the plume changing from translucent to opaque with rock dust.
tonne: metric unit equal to 1,000 kilograms, 2,204.6 lbs, or 1.1 English tons.
microradian: a measure of angle equivalent to 0.000057 degrees.
ppm: parts-per-million; 10,000 ppm = 1 %.
littoral cone: usually small cones built near active ocean entries; the cones are constructed of tephra from steam explosions that are sometimes produced when 1,150 degree C lava enters the 25 degree C ocean.
incandescence: the production of visible light from a hot surface. The color of the light is related to the temperature of the surface. Some surfaces can display dull red incandescence at temperatures as low as 430 degrees Centigrade (806 degrees Fahrenheit). By contrast, molten lava displays bright orange to orange-yellow light from surfaces that are hotter than 900 degrees C (1,650 degrees F).
tephra: all material deposited by fallout from an eruption-related plume, regardless of size.
ash: tephra less than 2 mm (5/64 inches) in size.
TEB: Thanksgiving Eve Breakout, the designation used for lava flows that started with a breakout on November 21, 2007.
DI tilt event: DI is an abbreviation for 'deflation-inflation' and describes a volcanic event of uncertain significance. DI events are recorded by tiltmeters at Kilauea summit as an abrupt deflation of up to a few microradians in magnitude lasting several hours to 2-3 days followed by an abrupt inflation of approximately equal magnitude. The tilt events are usually accompanied by an increase in summit tremor during the deflation phase. A careful analysis of these events suggests that they may be related to changes in magma supply to a storage reservoir at less than 1 km depth, just east of Halema`uma`u crater. Usually, though not always, these changes propagate through the magma conduit from the summit to the eruption site, as many of the DI events at Kilauea summit are also recorded at a tiltmeter at Pu`u `O`o, delayed by 1-2 hours. DI events often correlate with lava pulses and/or pauses in the eruption at the Pu`u `O`o/July 21/TEB vents.
Maps, photos, webcam views, and other information about Kilauea Volcano are available at http://volcano.wr.usgs.gov/kilaueastatus.php. A daily update summary is available by phone at (808) 967-8862.
A map with details of earthquakes located within the past two weeks can be found at http://tux.wr.usgs.gov/
A definition of alert levels can be found at http://volcanoes.usgs.gov/2006/warnschemes.html Details...
LONG VALLEY OBSERVATORY CURRENT STATUS REPORT issued Jul 23, 2008 09:17 PDT Volcano Alert Level NORMAL - Aviation Color Code GREEN
The realtime detection system did not locate any earthquakes in the vicinity of Long Valley caldera since the last update at 9:24 AM on July 22. Details...
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