فارسي | English
  About Us | About Iran | Contact Us | Staff Info[Geoportal Info] [Maps] [Mining Info] [Other Activities]  
  News | Events | Photo Gallery | Downloads | Links | Kids  Search    Region    Scale    Subject   :Access to information by   Home | Newest   

New titles:
 Govt electricity supply report 'will not save US coal'
 The Legacy of the 1992 Nicaragua Tsunami
 How friction evolves during an earthquake (By simulating quakes in a lab, engineers study the way that friction changes along a fault during a seismic event)
 USGS on Fire: It's not a matter of
 Ancient Earth's hot interior created 'graveyard' of continental slabs
 Supervolcanoes: A key to America's electric future?
 USGS publishes a new blueprint that can help make subduction zone areas more resilient
 Loss of Reflectivity in the Arctic Doubles Estimate of Climate Models
 How Do Diamonds Form?
 Russians Will Be First To Explore Untouched Antarctic Lake Vostok, In Hunt For Weird Life Forms
News Report
New Volcanic Island Unveils Explosive Past
NGDIR News Section-- A recent volcanic eruption near Tonga in the southwest Pacific created a new island, giving scientists a rare opportunity to explore the volcanic record of this remote region.
   In late December 2014, an undersea volcano erupted between two small islands in the Tonga volcanic arc northeast of New Zealand, sending steam and dense ash plumes high into the air. By the time the eruption ended about 5 weeks later, a new island had formed, eventually bridging the gap between the original islands. Winds and ocean waves then began rapidly reshaping the newly emerged volcanic cone.
   Ten months after the eruption, we visited the new island, which we unofficially nicknamed Hunga Island. There, we attempted to characterize the volcanology of the eruption, begin tracking the rate of erosion on the new island, and assemble a history of volcanism in this region of the southwest Pacific. Our findings reveal a shallow submarine volcanic caldera adjacent to the new volcanic island, and they highlight how incomplete the volcanic record can be at remote oceanic volcanoes.
   Signs of Eruption
   The uninhabited islands of Hunga Tonga and Hunga Ha'apai lie 65 kilometers north of Nuku'alofa, the capital city of the Kingdom of Tonga. Between 19 December 2014 and 28 January 2015, residents of Nuku'alofa witnessed several large volcanic plumes rising from an eruption in the direction of the two islands [Global Volcanism Program, 2015].
   The plumes were the result of an explosive interaction between seawater and magma rising from a plateau about 150 meters below the ocean surface. The plateau is part of Hunga, a massive, submerged volcanic edifice that rises more than 2000 meters from the surrounding seafloor and the site of volcanic activity as recently as 1988 and 2009 [Global Volcanism Program, 2009].
   The 2014-2015 Hunga eruption deposited material between the islands of Hunga Tonga and Hunga Ha'apai, initially creating an isolated third island before connecting with Hunga Ha'apai. In less than 3 weeks, the eruption built up a circular area of land with a diameter of about 2 kilometers and a height of 120 meters.
   A Violent Volcano Under the Sea
   Hunga Ha'apai, Hunga Tonga, and a reef to their south sit on the rim of a submarine caldera known as Hunga Tonga-Hunga Ha'apai. The islands and reef are the only surface features betraying the presence of the largely submerged Hunga volcano.
   Hunga volcano is one of many volcanoes in the Tonga-Kermadec volcanic arc that formed in response to subduction of the Pacific Plate beneath the Indo-Australian Plate.
   Many highly explosive eruptions along this chain have had significant regional consequences. These occurrences suggest that Hunga volcano may itself have had a similarly violent past.
   Past research indicates that radiating, outward dipping lava flows and pyroclastic deposits on the two older Hunga islands represent small remnants of the rim of a very large volcano surrounding a caldera structure [Bryan et al., 1972]. This volcano may have suffered catastrophic collapse or prolonged erosion, obscuring it from view.
   Field Observations
   In November 2015, we conducted a land and ocean survey of Hunga Tonga-Hunga Ha'apai and the new island. Our goals were to characterize the recent eruption and collect baseline quantitative topographic data for tracking erosion rates. We also wanted to assemble a longer history of the area's volcanic and tsunami activity by surveying the older Hunga islands and surrounding shallow waters.
   On the new island, we discovered that coarse deposits from falling water-rich jets of pyroclastic rock fragments form the lower beds of the cone, consistent with videos and photos of the eruption in progress. Where waves have cut into the shoreline, the pyroclastic deposits appear poorly consolidated and poorly sorted.
   The upper part of the cone is steeper and reflects a gradual "drying" (decrease in water interaction with magma) of the eruption as it proceeded. This upper region is made up of thin, fine-grained beds of ash deposits, interspersed with ash-dominated sediments typical of lateral currents of particles, air, and steam.
   The cone reached its maximum diameter by 7 January 2015 but continued to increase in height over the next 2 weeks. Once the vent was completely surrounded by pyroclastic deposits, much higher eruption columns began. Such Surtseyan eruptions-from a shallow sea or lake water-have only rarely been witnessed since the phenomenon was first seen during the formation of Surtsey, Iceland, in 1963 [Kokelaar, 1983].
   Rilling of the island's surface-forming dendritic erosion patterns-started during the cone growth, but it accelerated with rainfall once the eruption ceased. In addition, wave erosion began to rapidly attack the base of the island. Wave erosion was strongest on the southern side of the cone, exposed to the southeast trade winds and associated ocean swells. There, the island has shrunk by more than 500 meters from its initial posteruption shore, leaving 40-meter-high collapsing cliffs.
   In the 2.5 years since its formation, the primary volcanic cone lost about 40% of its original footprint, which spanned roughly 8 square kilometers. However, the island has remained roughly the same in overall area because erosion has been matched by long-coast redisposition of the volcanic material in beach bars, altering the island's shape.
   Taking Samples
   Shortly after the eruption, we carried out a photogrammetric survey using a drone and real-time kinematic GPS control points to provide a baseline for future monitoring.
   We collected samples to chemically characterize the new volcanic material and compare it with deposits of the broader volcano. On the older Hunga Ha'apai islands, we found welded pumice-rich ignimbrite units and nonwelded pyroclastic flow deposits, laid down by superheated flows of gas and particles. Such deposits attest to past huge explosive eruptions from this long-lived volcano.
   One pyroclastic flow deposit contained charcoal, which we dated to the period 1040-1180 CE. This deposit correlates closely in age and chemistry to ashfall deposits found on Tongatapu Island, 65 kilometers to the southwest [Cronin, 2015]. It also corresponds, within uncertainty bounds, to an unknown tropical eruption in 1108 CE that produced more than 1C of global cooling [Sigl et al., 2015].
   Seafloor Mapping
   We also mapped the seafloor surrounding the new island at a resolution of about 1 meter using a WASSP multibeam sounder.
   The seafloor survey revealed a large closed depression to the south, consistent with the caldera postulated by Bryan et al. [1972]. The depression is approximately 150 meters deep and measures about 4 . 2 kilometers, with its northern and southern portions filled by younger volcanic deposits.
   A broad, shallow area is associated with the 2009 eruptions south of the island formed in 2015 and a chain of cones formed in 1988 to the southeast. Numerous other cones surround the rim of the caldera.
   The caldera likely formed when an older Hunga edifice collapsed violently into the sea. This collapse may be the source of the unknown South Pacific eruption about 1000 years ago.
   Next Steps
   Our first observations highlight how rapidly new volcanic forms are eroded in this area and imply that the volcanic record in the Tonga region is extremely fragmentary. In future visits, we will continue investigating past eruptions while extending submarine surveys and sampling around the new island to monitor the ongoing changes in response to storms and other events.
   By EOS

Publications  Library
Glossary  Papers
FAQ  Members
Job Offer  Training
• NanoBioEarth Database 
• Medical Geology Database 
• Geological Atlas of Roads 
• 4th National Development Plan 
• Marine Geology 
• Geography information 
• Mines and Deposits of Iran 
• Landslide Database of Iran 
• Exploration Area DB 
• Copper Database 
• Gold Database  
• Geoscience Laboratories 
• Mineral Information 
• Bibliographic Database 
• Geochemistry Database 
• Earthquake database 
• Abandoned mines DB of Iran 
• Mineral processing database 
• Minerals database 
Login Name:
Sign Up for membership ]
   Others Activities:• Geo Hazard Of South Caspian • Geoscience database of ALBA • Geoscience Database of ECO 
• GEOLOGICAL SURVEY OF IRAN • Tajikistan Geoscience Database • Geo Database of Venezuela • 4th National Development Plan 
• Export & Import Regulation Act     
Maps:• Map of Iran's Last Earthquake • Distribution Map of mineral Processing Plants 
• Mineral Distribution Map of Iran • Geosciences laboratories distribution map of Iran • Orohydrographic Map of Iran 
• Select state on iran map • Geological Map of Iran(1:1000, 000 Scale) • 2500 K Magnetic Lineament Map of Iran 
• Map of Iran's Earthquake    
Best viewed:1024*768
National Geoscience Database Of IRAN
Contact Mail:Info@ngdir.ir
 Search with:           
Designed by Payvand Software Group  Privacy | Copyright | Disclaimer