Morphology, mineral and geochemical investigations were carried out on two selected soil pedons (ZA and TO) developed on a late Quaternary-aged strombolian cone to better understand andosolization processes in Mount B...Morphology, mineral and geochemical investigations were carried out on two selected soil pedons (ZA and TO) developed on a late Quaternary-aged strombolian cone to better understand andosolization processes in Mount Bambouto, Cameroon. Both pedons have A-BC-C horizonation. They have thick surface (A) horizon with bulk density -3, Alo + 0.5Feo about 2% and P retention >90%. Mineral association consists predominantly of kaolinite, gibbsite, goe- thite, organometal complexes and trace amount of ferrihydrite and allophane. The Ki values between 1.1 and 1.6, the low TRB (45 to 67 mg kg-1), the important IMob (20% to 24%), the CIA between 60% and 70% and the EFs above 1.16 for Al and Fe, and below 0.6 for Si indicate sparingly hydrolysis process in subsoil during which released Al, Fe and Si form allophanic or ferrihydrite minerals undergo crystallization into kaolinite, gibbsite and goethite, respectively. At topsoil, part of released Al (and Fe) is organically bounded with organic acids to form organometal complexes.展开更多
In this work we focus our attention on micro-scale textural observations and chemical analysis of the surface of ash particles erupted from ordinary activity at Stromboli volcano (Aeolian Islands, Italy). Ashes are re...In this work we focus our attention on micro-scale textural observations and chemical analysis of the surface of ash particles erupted from ordinary activity at Stromboli volcano (Aeolian Islands, Italy). Ashes are related to three vent systems: NE1, NE2 and SW showing different eruptive styles. Samples were collected during three campaigns: 1-5 September 2008;20, 22 September 2008 and 18 June 2009, with two different methods: collection on a clean surface downwind and use of remotely controlled, electrically propelled aeromodels, which penetrate directly in the eruptive plume and collect ash samples that are less affected by transport-related sorting processes. A micro-textural approach has been conducted working at step: from preliminary observations under binocular microscope on a medium number of 700 particles, to thin sections and sub-micron investigations, using high resolution instruments. Micro-texture and morphology of ash particles were observed under FE-SEM, at high magnification (30,000/50,000×) measuring the main shape parameters (area, perimeter, max length, compactness, Feret’s diameter, Heywood’s diameter and elongation). Ashes are made up by a wide spectrum of fragments whose end-members are represented by two main textural types with different colour, shape, internal textures and vesicularity named “Type a” and “Type b”. “Type a” shows great similarities with fragments called “tachilite” while “Type b” fragments are very similar to the named “sideromelane” fragments. Fragments with intermediate textural features are present and named as “Type a1” and “Type b1”, respectively. The relative abundances of each type of fragments greatly vary in samples collected from different groups of vents. Chemical analysis of the external surfaces indicates that all the different grain types underwent alteration phenomena and precipitation of neo-formation minerals on their surfaces. The alteration is dependent from the atmospheric conditions around the vent and not from the type of fragments. During the periods of sampling, ash erupted from individual explosions of different vents, does not show big differences in morphology and chemistry of surface features, but mainly in terms of relative proportion of fragments. “Type b” fragments predominate in the ash erupted from typical strombolian activity whereas “Type a” fragments are ubiquitous.展开更多
Jeju Island,Korea,was formed through volcanic activity from approximately 1.8 million to 1,000 years ago.The island was designated a Global Geopark in 2010 in recognition of its diverse geoheritage.As part of a specia...Jeju Island,Korea,was formed through volcanic activity from approximately 1.8 million to 1,000 years ago.The island was designated a Global Geopark in 2010 in recognition of its diverse geoheritage.As part of a special edition for the International Geological Congress 2024,this article shares the latest scholarship on Jeju’s volcanic geoheritage sites to enhance public understanding of the island’s geoheritage as earlier misconceptions continue to spread through books,websites,and information boards,etc.Despite long being interpreted as a typical shield volcano,for example,Mt.Hallasan has been recategorized as a polygenetic and composite volcano that formed through Strombolian eruptions,lava effusions,and magma intrusions from 200,000 to 17,000 years ago.Moreover,although once interpreted as a single scoria cone that formed a thousand years ago,Biyangdo Island(Biyangbong)formed through subaerial volcanic eruptions 26,000 years ago that produced both a scoria cone and a spatter cone.This research is presented with the latest research on other volcano-related Jeju Island Global Geopark geosites,including Suwolbong Tuff Cone and Seongsan Ilchulbong Tuff Ring.Alongside regular research and monitoring,public awareness is essential to ensure sustainable protection due to increasing rockfalls caused by rising sea levels at coastal geosites and climate changeexacerbated freeze-thaw weathering at inland sites on Mt.Hallasan.展开更多
The Barren Island volcano in the Western Sunda Arc has displayed explosive Strombolian eruptions for more than two decades.This recent explosive event,together with the historic and prehistoric volcanic landforms,pres...The Barren Island volcano in the Western Sunda Arc has displayed explosive Strombolian eruptions for more than two decades.This recent explosive event,together with the historic and prehistoric volcanic landforms,present reliable information about explosive Strombolian eruptions and the volcanological evolution of the Barren Island volcano.This study is a re-evaluation of existing knowledge and incorporates new information and interpretations of the recent and past volcanic activity on Barren Island.Direct observations of explosive eruptions since 1991 showed discrete events of bursting and ballistic transport of blocks and formation of sustained ash plumes,indicating Strombolian and violent Strombolian eruptions.展开更多
文摘Morphology, mineral and geochemical investigations were carried out on two selected soil pedons (ZA and TO) developed on a late Quaternary-aged strombolian cone to better understand andosolization processes in Mount Bambouto, Cameroon. Both pedons have A-BC-C horizonation. They have thick surface (A) horizon with bulk density -3, Alo + 0.5Feo about 2% and P retention >90%. Mineral association consists predominantly of kaolinite, gibbsite, goe- thite, organometal complexes and trace amount of ferrihydrite and allophane. The Ki values between 1.1 and 1.6, the low TRB (45 to 67 mg kg-1), the important IMob (20% to 24%), the CIA between 60% and 70% and the EFs above 1.16 for Al and Fe, and below 0.6 for Si indicate sparingly hydrolysis process in subsoil during which released Al, Fe and Si form allophanic or ferrihydrite minerals undergo crystallization into kaolinite, gibbsite and goethite, respectively. At topsoil, part of released Al (and Fe) is organically bounded with organic acids to form organometal complexes.
文摘In this work we focus our attention on micro-scale textural observations and chemical analysis of the surface of ash particles erupted from ordinary activity at Stromboli volcano (Aeolian Islands, Italy). Ashes are related to three vent systems: NE1, NE2 and SW showing different eruptive styles. Samples were collected during three campaigns: 1-5 September 2008;20, 22 September 2008 and 18 June 2009, with two different methods: collection on a clean surface downwind and use of remotely controlled, electrically propelled aeromodels, which penetrate directly in the eruptive plume and collect ash samples that are less affected by transport-related sorting processes. A micro-textural approach has been conducted working at step: from preliminary observations under binocular microscope on a medium number of 700 particles, to thin sections and sub-micron investigations, using high resolution instruments. Micro-texture and morphology of ash particles were observed under FE-SEM, at high magnification (30,000/50,000×) measuring the main shape parameters (area, perimeter, max length, compactness, Feret’s diameter, Heywood’s diameter and elongation). Ashes are made up by a wide spectrum of fragments whose end-members are represented by two main textural types with different colour, shape, internal textures and vesicularity named “Type a” and “Type b”. “Type a” shows great similarities with fragments called “tachilite” while “Type b” fragments are very similar to the named “sideromelane” fragments. Fragments with intermediate textural features are present and named as “Type a1” and “Type b1”, respectively. The relative abundances of each type of fragments greatly vary in samples collected from different groups of vents. Chemical analysis of the external surfaces indicates that all the different grain types underwent alteration phenomena and precipitation of neo-formation minerals on their surfaces. The alteration is dependent from the atmospheric conditions around the vent and not from the type of fragments. During the periods of sampling, ash erupted from individual explosions of different vents, does not show big differences in morphology and chemistry of surface features, but mainly in terms of relative proportion of fragments. “Type b” fragments predominate in the ash erupted from typical strombolian activity whereas “Type a” fragments are ubiquitous.
基金supported by the Jeju World Heritage Office of Jeju Special Self-Governing Province.
文摘Jeju Island,Korea,was formed through volcanic activity from approximately 1.8 million to 1,000 years ago.The island was designated a Global Geopark in 2010 in recognition of its diverse geoheritage.As part of a special edition for the International Geological Congress 2024,this article shares the latest scholarship on Jeju’s volcanic geoheritage sites to enhance public understanding of the island’s geoheritage as earlier misconceptions continue to spread through books,websites,and information boards,etc.Despite long being interpreted as a typical shield volcano,for example,Mt.Hallasan has been recategorized as a polygenetic and composite volcano that formed through Strombolian eruptions,lava effusions,and magma intrusions from 200,000 to 17,000 years ago.Moreover,although once interpreted as a single scoria cone that formed a thousand years ago,Biyangdo Island(Biyangbong)formed through subaerial volcanic eruptions 26,000 years ago that produced both a scoria cone and a spatter cone.This research is presented with the latest research on other volcano-related Jeju Island Global Geopark geosites,including Suwolbong Tuff Cone and Seongsan Ilchulbong Tuff Ring.Alongside regular research and monitoring,public awareness is essential to ensure sustainable protection due to increasing rockfalls caused by rising sea levels at coastal geosites and climate changeexacerbated freeze-thaw weathering at inland sites on Mt.Hallasan.
基金sponsored by DST,Govt of India to PCB under USERS scheme(file no.SB/UR/14/2012).
文摘The Barren Island volcano in the Western Sunda Arc has displayed explosive Strombolian eruptions for more than two decades.This recent explosive event,together with the historic and prehistoric volcanic landforms,present reliable information about explosive Strombolian eruptions and the volcanological evolution of the Barren Island volcano.This study is a re-evaluation of existing knowledge and incorporates new information and interpretations of the recent and past volcanic activity on Barren Island.Direct observations of explosive eruptions since 1991 showed discrete events of bursting and ballistic transport of blocks and formation of sustained ash plumes,indicating Strombolian and violent Strombolian eruptions.
