Indochinite tektites (billitonites) from the Pleistocene of Indonesia. (FMNH Me 2326, Field Museum of Natural History, Chicago, Illinois, USA)
Large and small impacts have affected Earth since its formation 4.55 billion years ago. Compared with the intensely pitted and cratered Moon, Earth has relatively few preserved impact craters, because they have been destroyed by water erosion, glacial erosion, and plate tectonics. Impact events are accompanied by significant heating, which results in melting of much of the ejected pulverized bedrock. The melted material cools quickly and falls back to Earth in the form of tektites - impact splash glasses. Tektites are principally composed of amorphous silica (SiO2). Broken surfaces show a conchoidal fracture. Tektites from different impact events are given different names.
Indochinites are black-colored, moderately common tektites from southeastern Asia that typically are subspherical to teardrop-shaped to dumbbell-shaped. They are found throughout the Australasian Tektite Strewn Field (a.k.a. Indochinite Tektite Strewn Field). This strewn field is huge - it's estimated to cover 10 to 20% of Earth's surface. Indochinites have been found from Madagascar to Antarctica to Tasmania to South China. Samples from different geographic areas are often given different names (e.g., australites, thailandites, malaysianites, philippinites, billitonites, vietnamites), but they were all apparently formed by the same event. The site of the impact crater has long been a mystery, but has now been identified as likely buried by basaltic lava flows in Laos, southeastern Asia (Sieh et al., 2019). The age of indochinites has been reported to be about 783 to 803 ka.
Locality: unrecorded/undisclosed site on Billiton Island (a.k.a. Belitung Island), Indonesia
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Reference cited:
Sieh et al. (2019) - Australasian impact crater buried under the Bolaven Volcanic Field, southern Laos. Proceedings of the National Academy of Sciences 117: 1346-1353.
Tags: tektite tektites indochinite indochinites impact splash glass glasses Australasian Strewn Field billitonite bilitonites Billiton Island Belitung Indonesia
Rhyodacite pumice from the late Holocene of Indonesia. (8.6 cm across at its widest)
Krakatoa (also spelled Krakatau) is a subduction zone volcano in Indonesia’s Sunda Strait between the large islands of Sumatra and Java. It had a catastrophic eruption in late August 1883, culminating in an enormous steam explosion as its magma chamber collapsed. The steam explosion generated a large tsunami, which wiped out many villages in surrounding areas. Tens of thousands were killed. The steam explosion was heard several thousand miles away, and the shock wave went around the entire globe. For some time after, Krakatoa ash high in the atmosphere resulted in gorgeous orangish-red sunsets around the world. An artist in Scandinavia was inspired by the Krakatoa sunsets to make the famous surrealistic painting “The Scream”.
Krakatoa’s eruption resulted in the generation of enormous volumes of ash and pumice. Sailors noticed floating Krakatoa pumice for months afterward, sometimes mixed with the bodies and bones of victims killed by the tsunami. The rock shown above is a pumice piece from Krakatoa’s August 1883 eruption - it floated in the Indian Ocean Basin for almost a year before washing ashore in eastern Africa. Most of Krakatoa’s erupted ash and pumice is rhyodacite. A small percentage of the erupted material is dacite and andesite.
As are all pumice samples, this rock consists of highly porous, finely vesiculated volcanic glass. The abundance of gas bubbles (frothy texture) makes the rock lightweight. Many of the vesicles (gas bubbles) are noticeably stretched.
Collection locality: Takwa Beach, southeastern shores of Manda Island, Lamu Archipelago, coastal Kenya, eastern Africa
Tags: pumice Krakatoa Indonesia 1883 Krakatau
Rhyodacite pumice from the late Holocene of Indonesia. (field of view ~2.7 cm across)
Krakatoa (also spelled Krakatau) is a subduction zone volcano in Indonesia’s Sunda Strait between the large islands of Sumatra and Java. It had a catastrophic eruption in late August 1883, culminating in an enormous steam explosion as its magma chamber collapsed. The steam explosion generated a large tsunami, which wiped out many villages in surrounding areas. Tens of thousands were killed. The steam explosion was heard several thousand miles away, and the shock wave went around the entire globe. For some time after, Krakatoa ash high in the atmosphere resulted in gorgeous orangish-red sunsets around the world. An artist in Scandinavia was inspired by the Krakatoa sunsets to make the famous surrealistic painting “The Scream”.
Krakatoa’s eruption resulted in the generation of enormous volumes of ash and pumice. Sailors noticed floating Krakatoa pumice for months afterward, sometimes mixed with the bodies and bones of victims killed by the tsunami. The rock shown above is a pumice piece from Krakatoa’s August 1883 eruption - it floated in the Indian Ocean Basin for almost a year before washing ashore in eastern Africa. Most of Krakatoa’s erupted ash and pumice is rhyodacite. A small percentage of the erupted material is dacite and andesite.
As are all pumice samples, this rock consists of highly porous, finely vesiculated volcanic glass. The abundance of gas bubbles (frothy texture) makes the rock lightweight. Many of the vesicles (gas bubbles) are noticeably stretched.
Collection locality: Takwa Beach, southeastern shores of Manda Island, Lamu Archipelago, coastal Kenya, eastern Africa
Tags: pumice Krakatoa Indonesia 1883 Krakatau
Rhyodacite pumice from the late Holocene of Indonesia. (CMNH 12513, Cleveland Museum of Natural History, Cleveland, Ohio, USA)
Krakatoa (also spelled Krakatau) is a subduction zone volcano in Indonesia’s Sunda Strait between the large islands of Sumatra and Java. It had a catastrophic eruption in late August 1883, culminating in an enormous steam explosion as its magma chamber collapsed. The steam explosion generated a large tsunami, which wiped out many villages in surrounding areas. Tens of thousands were killed. The steam explosion was heard several thousand miles away, and the shock wave went around the entire globe. For some time after, Krakatoa ash high in the atmosphere resulted in gorgeous orangish-red sunsets around the world. An artist in Scandinavia was inspired by the Krakatoa sunsets to make the famous surrealistic painting “The Scream”.
Krakatoa’s eruption resulted in the generation of enormous volumes of ash and pumice. Sailors noticed floating Krakatoa pumice for months afterward, sometimes mixed with the bodies and bones of victims killed by the tsunami. The rock shown above is a large pumice piece from Krakatoa’s August 1883 eruption - it was recovered floating in the ocean. Most of Krakatoa’s erupted ash and pumice is rhyodacite. A small percentage of the erupted material is dacite and andesite.
The lower (incomplete) vintage label refers to how many thousands of people were killed from the eruption. The upper vintage label reads: “From the burning mountain of Krackatao. Ship H.W. Dudley sailed three days through dead bodies and pumice stone [from] this island.”
Tags: pumice Krakatoa Indonesia 1883 Krakatau
Porphyritic basaltic andesite (10.6 cm across) - this juvenile lava is sample from a 14 June 2006 block & ash flow (pyroclastic flow) from Mt. Merapi. Historically, most of Merapi’s lavas are basaltic andesites that are highly porphyritic (more than half the rock volume). Phenocrysts are commonly plagioclase feldspar & pyroxene.
Locality: pyroclastic flow deposit at ~1200 meters elevation in the hamlet of Bebeng, village of Kaliadem, ~30 km from Yogyakarta, central Java, Indonesia (7º 34’ 57” South, 110º 26’ 51” East).
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One of the more recently active volcanoes is Mt. Merapi in central Java Island, Indonesia. Mt. Merapi has had frequent eruptions for at least the last 2000 years, with relatively quiet intervals at ~600-700 years ago & at ~1100-1400 years ago (see Gertisser & Keller, 2003). Between 20 and 30 eruption intervals have been recorded in the 1800s and in the 1900s. From May to June 2006, Merapi was observed to issue lava flows, ash columns, and ash flows.
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Some info. from:
Gertisser & Keller (2003) - Temporal variations in magma composition at Merapi Volcano (central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity. Journal of Volcanology and Geothermal Research 123: 1-23.
Tags: Merapi basaltic andesite 2006 pyroclastic flow volcanic ash eruption Indonesia Java