Magnitude 6.7 quake strikes south of Crete

Strong 6.7 Mw quake strikes south of Crete, Greece

Magnitude 6.7 mainshock followed by at least one aftershock measuring 4.9 Mw struck south of the island of Crete, Greece.

10-degree Map Centered at 35°N,25°E

Location Map. Note location of Santorini. Original Map: USGS

Major Tectonic Boundaries: Subduction Zones -purple (Source: USGS)

Major Tectonic Boundaries: Subduction Zones -purple (Source: USGS)

Details of the Mainshock:

• Magnitude: 6.7
• Date-Time:
  • Wednesday, July 01, 2009 at 09:30:12 UTC
  • Wednesday, July 01, 2009 at 12:30:12 PM at epicenter
• Location:  34.188°N, 25.426°E
• Depth:  38 km (23.6 miles)
• Region CRETE, GREECE
• Distances
  • 130 km (80 miles) S of Iraklion, Crete, Greece
  • 195 km (120 miles) SE of Chania, Crete, Greece
  • 270 km (165 miles) NNE of Tubruq, Libya
  • 450 km (280 miles) SSE of ATHENS, Greece
• Location Uncertainty:  horizontal +/- 7.1 km (4.4 miles); depth +/- 12.8 km (8.0 miles)
• Parameters:  NST= 51, Nph= 51, Dmin=131.6 km, Rmss=1.19 sec, Gp= 72°, M-type=teleseismic moment magnitude (Mw), Version=7
• Source: USGS NEIC (WDCS-D)
• Event ID:  us2009ina1

What’s happening at Santorini?

For Background Information See: Volcanoes, Santorini Eruption and Crops Failure in China

Santorini

Country: Greece
Subregion Name: Greece
Volcano Type: Shield volcanoes
Volcano Status: Historical
Last Known Eruption: 1950
Summit Elevation: 367 m 1,204 feet
Latitude: 36.404°N 36°24’13″N
Longitude: 25.396°E 25°23’47″E
Source: GVP

Renowned Santorini (Thera), with its steep-walled caldera rim draped by whitewashed villages overlooking an active volcanic island in the center of a caldera bay, is one of the scenic highlights of the Aegean. The circular island group is composed of overlapping shield volcanoes cut by at least four partially overlapping calderas. The oldest southern caldera was formed about 180,000 years before present (BP), followed by the Skaros caldera about 70,000 years BP, and then the Cape Riva caldera about 21,000 years BP. The youngest caldera formed about 3600 years BP during the Late-Bronze-Age Minoan eruption that forced abandonment of the thriving Aegean Sea island. Post-Minoan eruptions beginning in 197 BC constructed a series of lava domes and flows that form two islands near the center of the caldera. A submarine eruption took place in 1650 AD outside the caldera NE of Thera. The latest eruption at Santorini produced a small lava dome and flow in 1950, accompanied by explosive activity. Photo by Lee Siebert, 1994 (Smithsonian Institution). Caption: Global Volcanism Program.

Geographic setting

Santorini is an active volcano in the South Aegean Sea about 120 km north of
Crete, its location being 36.4oN, 25.4oE, and belongs to the Cycladic islands.
Santorini is a group of 5 islands:
1. The main island Thira (75,8 km², ca. 7000 inhabitants)
2. Thirasia (9,3 km², ca. 250 inhabitants)
3. Aspronisi (0,1 km², uninhabited)
4. Palea Kameni (0,5 km², 1 inhabitant) 5. Nea Kameni (3,4 km², uninhabited  (http://www.geophysicsonline.gr)

On June 13, 2009 GR Reporter (www.GRREPORTER.INFO) wrote:

Computer generated image of Columbus. Source: GR Reporter

The submarine volcano, Columbus, located about 6.5 km south-east of Santorini in the Aegean Sea, is now the focus of “great interest” for Greek and German geologists.
“They have registered constant earthquakes of 4 Richter, hot air eruptions and continuous changes in the sea floor around the crater. The volcano is 470 meters high and reaches down to 17 meters beneath the sea floor. Its crater’s width is out of proportion- 1.5 kilometers. Complex submarine equipment has shown that Columbus’s volcanic activity never stops. It is the reason for the frequent earthquakes and constant changes in the surface around the crater.”

“The distortion of the sea floor is minor but it can be seen on the walls of the crater and in the 10-15-kilometers perimeter around it,” says Martin Heds from the Geology and Seismology institute to the Hamburg University.

According to Heds, “this does not indicate an eruption in near future.” The last known eruption of Columbus occurred in 1650.

“‘Reservoirs’” filled with hot water, reaching 200 degrees centigrade, resembling under-water fire places and releasing different kinds of gases- mostly carbon dioxide and hydrogen sulphide,” were discovered in the vicinity of Columbus.

A 5-km wide magma chamber is believed to be situated under the volcano. Lava is constantly spewed out of the chamber, GR Reporter suggested.

Tectonic Setting

The volcanic complex of Santorini is the most active part of the South Aegean Volcanic Arc. This volcanic arc is about 500 km long and 20 to 40 km wide and extends from the mainland of Greece through the islands of Aegina, Methana, Poros, Milos, Santorini, Kos, Yali, Nisyros and the Bodrum peninsula in Turkey. It is characterized by earthquakes at depths of 150-170 km that mark the subduction of the African underneath the Eurasian plate, more precisely the Aegean subplate, at a rate of up to 5 cm per year in a northeasterly direction.  (http://www.geophysicsonline.gr)

The South Aegean Volcanic Arc and the tectonic setting of Santorini. (http://www.geophysicsonline.gr) Click Image to Enlarge.

Geology of Santorini

Non-volcanic rocks are exposed on Santorini at the Profitis Ilias Mountain, Mesa Vouno, the Gavrillos ridge, Pirgos, Monolithos and the inner side of the caldera wall between Cape Plaka and Athinios.

They represent a former non-volcanic island of about 9×6 km extension similar to neighboring Cycladic islands like Anaphe, Ios or Amorgos. The rocks consist of metamorphosed limestone and schist from Triassic to Tertiary time folded during the Alpine folding. The observed metamorphose grade is a blue-schist faciesresulting from tectonic deformation by the plate collision in the Oligocene to Miocene. At Athinios a 9.5 million year old Miocene granite intrusion has been found; it is part of the Cycladic Granitic Province and is the source of ore minerals including talc, chalcopyrite, chrysocolla, magnetite and others.(http://www.geophysicsonline.gr).

Simplified geologic map of Santorini. (http://www.geophysicsonline.gr  Sourced  From  http://www.geo.aau.dk/palstrat/tom/santorini_homepage/santorini_geology.htm). Click Image to Enlarge.

Related Links:

• Volcanoes, Santorini Eruption and Crops Failure in China
• FEWW Volcano Links
• Volcanoes
• FEWW Earthquake Links
• FEWW Earthquake Links

El Niño event almost certain: BOM

El Niño event likely, says Australia’s Bureau of Meteorology

More evidence of a developing El Niño event has emerged during the past fortnight, and computer forecasts show there’s very little chance of the development stalling or reversing. —BOM

Equatorial sea-surface temperatures are currently more than 1°C above normal in the eastern Pacific, while the Southern Oscillation Index (SOI) remains below zero at around −2, says BOM.

A sustained negative SOI is often associated with El Nino conditions.

BOM hopes to provide a clear picture of the situation in the Pacific by next week when their final June data are analyzed.

El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia.

Another adverse sign for southeastern Australian rainfall is the recent trend to positive values in the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI).

The next BOM update is available on July 8, 2009.

Last month FEWW reported US Climate Prediction Center as saying that conditions were favorable for a transition from ENSO-neutral to El Niño conditions during June – August 2009.

Click image to update and enlarge.

Images from Tropical Atmospheric Ocean project: NOAA

Summary of BOM Weekly Update:

• The Pacific Ocean sea surface is currently significantly warmer than the long-term average across most of the tropical Pacific, especially central to eastern areas.
• A large amount of the sub-surface water of the tropical Pacific is also warmer than the long-term average, particularly in the east.
• The latest 30-day SOI value is −2, while the monthly value for May was −5.
• Trade winds remain weaker than normal across the central equatorial Pacific.
• Cloudiness near the date-line is near-normal, and is yet to show a consistent trend towards El Niño conditions.
• All international climate models predict the tropical Pacific to continue to warm and to be above El Niño thresholds throughout most of the second half of 2009.

“Australia is the world’s fourth-largest wheat exporter and its grain production is still recovering from the worst drought in more than 100 years that reduced the 2006/07 crop to just 10.6 million tonnes and the 2007/08 crop to 13.0 million tonnes.” Reuters reported.

FEWW Moderators estimate that a new episode of El Niño, which would have devastating impact globally, could cause up to $500 billion in damages.

Related Links:

• El Niño could develop June – August 2009

• Recognizing El Niño
• El Niño and La Niña: Tracing the Dance of Ocean and Atmosphere
• TAO Diagrams

• El Niño Forecasts
• El Niño [Main Page]

See also comments section for latest updates.

Redoubt Volcano settling down?

Is Redoubt going back to sleep?

After Redoubt’s last explosive eruption about three month ago, the researchers at the Alaska Volcano Observatory say the volcano may be settling down. The aviation alert level has been lowered to code yellow (advisory), however, constant monitoring continues.

Redoubt has been oozing magma and ejecting steam since the last eruption on April 4, 2009.

“The last couple of months at Redoubt, we have been building a mountain,” said one of the researchers, referring to the colossal lava dome.

As of June 9, the giant dome had grown to approximately 67.5 million m3 in volume. the dome is unstable and can collapse  at any time, causing  explosions, and flooding the Drift River valley.

Redoubt from the east. Picture Date: July 01, 2009.  Image Creator: Cyrus Read. Image courtesy of AVO/USGS.

Redoubt photo taken by DFR Webcam. AVO. Camera is co-located with seismic station DFR, approximately 12.2 km NE of Redoubt.

ALASKA VOLCANO OBSERVATORY INFORMATION STATEMENT
Tuesday, June 30, 2009 4:38 PM AKDT (Wednesday, July 1, 2009 0038 UTC)
Redoubt Volcano
60°29’7″ N 152°44’38” W, Summit Elevation 10197 ft (3,108 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Extended Information Statement

The 2009 eruption of Redoubt volcano began March 15th, 2009 with a steam explosion. Between March 22nd and April 4th, Redoubt produced multiple significant explosions that sent ash and gas clouds to as high as 65,000 feet (19.8 km) above sea level. After April 4th, the eruption continued with extrusion of a lava dome within the summit crater, eventually producing a blocky lava flow that currently extends ~0.6 miles (1 km) down the north flank of the volcano. Redoubt entered its 14th week of eruptive activity the week of June 22nd. More …

Related Links:

• FEWW Volcano Links
• Volcanoes
• FEWW Earthquake Links
• FEWW Earthquake Links