Integrated regional scale view of Milos submarine hydrothermalism

<p>Submarine hydrothermal activity is common at the flanks of volcanic islands, and in some cases, occurring at very shallow water (0-100 meter depth). These sites are a key target for systematic seafloor mapping to understand the location, geometry and nature of hydrothermal discharge. These data are also critical for monitoring the temporal variability of these dynamic systems, while providing a context for instrumental measurements, sampling and other observations (e.g., temperature of outflow, chemistry, etc.). Here we present a systematic mapping of the Milos hydrothermal system in the Hellenic volcanic Arc, characterized by submarine gas emissions, high-temperature outflow, bacterial mats, precipitation of hydrothermal minerals, and small hydrothermal constructs and edifices. We have mapped this site at regional scales using satellite imagery (World-View2 images from the DigitalGlobe foundation), complemented with aerial photography acquired with drones, and high-resolution seafloor photomosaics (<1 cm resolution) from underwater imagery acquired by the autonomous underwater vehicle Sparus II (University of Girona). </p><p>Our drone and AUV mapping ground truths the correlation between patterns in satellite imagery and hydrothermal outflow, associated to mineral precipitates and/or bacterial mats at the seafloor. This mapping also reveals a clear organization of the hydrothermal outflow in sandy areas. In particular, polygonal patterns are common and often associated with inactive or actively bubbling pockmarks. These areas, showing white bacterial mats and hydrothermal precipitates, are rippled, suggesting that the hydrothermal precipitates do not consolidate the sediment. White precipitates display subseafloor temperatures >50°C at depths of 10 to 50 cm. The white areas are bound by bands of seafloor with a hummocky structure due to intense bioturbation, that obliterates the ripples, with widths of up to a few meters. This area shows subseafloor temperatures of 20-40°C, and corresponds to a transition from the high-temperature white zones and the seafloor with ripples and no hydrothermal precipitates. This area exhibits subseafloor temperatures similar to those of seawater, and can be associated with seagrass. These patterns reveal a clear organization of a narrowly focused hydrothermal outflow that controls the biological communities at the seafloor and subseafloor. We will discuss the implications of these observations to quantify hydrothermal fluxes in the study area.</p><p><br><br></p>

GUNUNGAPI BAWAH LAUT KAWIO BARAT, PERAIRAN SANGIHE, SULAWESI UTARA: AKTIVITAS HIDROTERMAL DAN MINERALISASI

Ekspedisi INDEX-SATAL 2010 telah mengungkapkan fenomena aktivitas hidrotermal di bawah perairan barat Kepulauan Sangihe pada Gunungapi Bawah Laut Kawio Barat dengan puncaknya yang berada pada kedalaman laut sekitar 1860 m dan kakinya pada kedalaman sekitar 5400 m. Penyelaman ROV (Remotely Operated Vehicle) Little Hercules di Gunungapi Kawio Barat yang dipusatkan di sisi baratlaut dari puncak gunung menyapu mulai kedalaman 3000 m hingga menuju ke arah puncak pada kedalaman 1860 m. Kelompok batuan dicirikan oleh bongkahan lava yang sudah pecah ditutupi sedimen halus berwarna abu-abu cerah; sedangkan pada sisi tenggara umumnya ditempati aliran lava bantal. Pada sisi baratdaya, tempat lembah dalam menoreh Gunungapi Kawio Barat dijumpai kepulan asap dari lereng bagian bawah yang akhirnya pada kedalaman sekitar 1890 m dijumpai aktivitas hidrotermal bawah laut yang merupakan suatu fenomena yang pertama kali direkam langsung dari bawahlaut perairan Indonesia. Fenomena yang terekam berupa pemunculan asap (smokers) di sepanjang rekahan (fissures), dicirikan oleh warna asap yang bervariasi dari putih, kuning atau abu-abu cerah yang kemungkinan menunjukkan indikasi perbedaan komposisi kimiawi dari fluida hidrotermal. Selain asap, teramati juga adanya gelembung cairan (panas) atau bubbles dari rekahan. Penemuan baru lainnya adalah adanya fluida hidrotermal muncul ke permukaan dan membentuk suatu cerobong hidrotermal atau chimney di daerah yang secara tektonik dikontrol oleh konvergensi lempeng. Batuan-batuan di sekitar rekahan hidrotermal (hydrothermal vent) umumnya telah terubah dengan dominasi warna putih hingga kelabu. Di sekitar rekahan hidrotermal diendapkan belerang berwarna kuning kehitaman. Mineralisasi kemungkinan terjadi di sekitar cerobong hidrotermal, terakumulasi membentuk endapan mineral yang ditunjukkan oleh warna coklat, abu-abu, dan kemerahan. Hal ini terutama teramati di sekitar cerobong yang sudah tidak mengeluarkan gelembung atau asap, serta dijumpai kehadiran endapan serakan butiran batuan atau mineral berwarna coklat atau hitam. Kata kunci: INDEX-SATAL 2010, aktivitas hidrotermal, ROV, asap hidrotermal, gelembung cairan, cerobong hidrotermal, konvergensi lempeng, mineralisasi INDEX-SATAL Expedition 2010 has revealed the phenomenon of hydrothermal activity in the western part of the Sangihe Waters in Kawio Barat Submarine Volcano with the peak which is located at 1860 m depths and the bottom at about 5400 m depths. A ROV (Remotely Operated Vehicle) "Little Hercules" dive in Kawio Barat was centered on the northwest side of the mountain began to sweep from the depths of 3000 m toward the top of 1860 m depths. The lithologic unit is characterized by the present of broken lavas covered with fine grey colored sediment whilist in the southeast side is composed of pillows lavas. In the southwest side, in which the deep valleys incise Kawio Barat, a clouds of smoke from the lower slopes are observed; finally at 1890 m depths a submarine hydrothermal activity is noted. This phenomenon represents the first submarine direct record made from the bottom of the Indonesian Waters. Those smokers phenomena are recorded along fissures, characterized by various colors of white, yellow to grey due to different chemical composition of hydrothermal fluids. Besides, the hot bubbles are also arised from the fissures. The other new discovery is the presence of hydrothermal chimney in the area of tectonically controlled by convergence plates. Rocks surrounding the hydrothermal vents are generally altered giving grey to white colors and the presence of dark yellow sulfur deposits. Mineralization may occur and accumulated in hydrothermal chimney and its surrounding to form brown-, grey-, and reddish- color deposits The latter are commonly found in inactive chimneys, indicated by the presence of dispersed brown and black color grains/chips of both sedimentary rocks or minerals as well. Keywords: INDEX-SATAL 2010, hydrothermal activity, ROV, hydrothermal smokers, bubbles, hydrothermal chimney, plate convergence, mineralization

GUNUNGAPI DAN KEGIATAN HIDROTERMAL BAWAHLAUT DI PERAIRAN SULAWESI UTARA: MINERALISASI DAN IMPLIKASI TEKTONIK

Ekspedisi kelautan IASSHA (Indonesia Australia Survey for Submarine Hydrothermal Activity) 2003 di kawasan perairan kepulauan Sangihe, Sulawesi utara telah mengidentifikasi Kawio Barat sebagai gunungapi bawahlaut dan indikasi kegiatan hidrotermal bawahlaut antara lain di Roa, Naung dan Banua Wuhu. Kegiatan gunungapi Kawio Barat dicirikan oleh anomali transmisi cahaya akibat adanya influk fluida (plume) pada airlaut dan tingginya kandungan gas metan dalam airlaut yang berhubungan dengan tingginya kandungan mangan. Kamera bawahlaut merekam koloni dari polychaete (“tube worms”) yang tumbuh pada batuan dimana gas metan muncul. Gejala mineralisasi pada batuan dicirikan adanya diseminasi pirit dan markasit pada batuan. Indikasi hidrotermal gunung Roa dicirikan adanya tingginya kandungan gas metan dalam airlaut sekitar puncak bukit sedangkan gejala aktivitas hidrotermal gunungapi Naung teridentifikasi berdasarkan tingginya kandungan gas metan dalam airlaut. Batuan penutup perbukitan Naung berupa andesit, batuapung dan breksi andesit. Perbukitan bawahlaut Banua Wuhu kemungkinan sebagai kawah parasit bawahlaut, terletak dilereng barat pulau gunung tidak aktif Mahengetang. Aktivitasnya ditunjukan oleh anomali lemah kekeruhan airlaut. Mineral ubahan berupa lempung, karbonat, klorit dan opak. Batuan terubah mengandung mineral halus pirit dan noda-noda kalkopirit. Kata Kunci: Gunungapi bawahlaut; hidrotermal, transmisi cahaya, influk fluida, gas metan, mangan, koloni dari polychaete, diseminasi pirit dan markasit, kawah parasit. The 2003 IASSHA (Indonesia Australia Survey for Submarine Hydrothermal Activity) expedition at Sangihe islands waters, North Sulawesi has identified the submarine volcano of Kawio Barat and also observed hydrothermal activities at Roa, Naung and Banua Wuhu. The activity of Kawio Barat volcano is characterized by light transmission anomaly with correlated to fluids influx (plume) and higher methane gas in sea waters correlates to higher manganese content. A submarine camera grab recorded a polychaete (“tube worms”) colony that growth on the rock where a methane gas seep. The pyrite disemination and marcasite indicates rocks mineralization. The Roa and Naung hydrothermal activities indicated by higher content of methane gas in sea water. The Naung volcano is covered by andesite, pumice and andesite breccia. The Banua Wuhu hill is possibly as a parasitic cone of active Mahengetang volcano. The weak anomaly transmissometer of sea water indicates a hydrothermal activity. The alteration mineral are clay, carbonate, chlorite and opaq mineral with fine mineral of pyrite and chalcopyrite. Keywords: Submarine volcano, hydrothermal, light transmission, fluids influx, methane gas, manganese, polychaete colony, pyrite dissemination and marcasite, parasitic cone.