Recent Activity at Loihi Volcano
Loihi August 1996 Event Response Expedition and followup cruises
Rock Gallery
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Sampling lavas on Loihi with the Pisces V submarine
| These photos are of polished thin sections from the rocks pictured below. They are being viewed through a microcrope in polarized light with crossed polars. The entire height of each image is magnified from about 1mm and 2.5mm, respectively. | |
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Large zoned crystal of clinopyroxene (gray) with two round inclusions of olivine (bluish green and brownish yellow). Many of the new Loihi rocks have this feature, which indicates that olivine started to form early and then reacted with the magma as clinopyroxene formed. |
Crystals of olivine (pinkish) and clinopyroxene (brown, gray and dark blue) in a glassy matrix (black). Note concentric zoning in pyroxenes. Clinopyroxene is rare in Hawaiian tholeiitic basalts.
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 P286-1 |
 P286-2 |
 P286-3 |
 P286-5 |
 P286-6 |
 P287-1 |
Visist the MBARI web site at: www.mbari.org/~davisa/Loi_lava.html to see some images of glass shards collected from volcanic sand deposits at Loihi.
Descriptions by David Clague
Dive P5-310, Oct.4, 1996, Frank Sansone observer. Dive was at the summit of Loihi Seamount in the newly formed collapse pit. Dive returned to vents discovered by Malahoff that are located on the upper northeast wall of the pit. Rock samples 1 to 4 and scoop sample are from same location: 18 54.590', 155 15.530', depth=1069m. Rock 1-Small pillow fragment collected in talus at end of dive on north side of Pele Pit. Sample has original glass surface on one surface. Lava is dense (2% vesicles) with very rare olivine crystals. Labelled P5-310-1. Rock 2- Small pillow fragment from same location as sample #1. There is a spalled glass surface on one side, but almost no usable glass. Same lithology as sample 1. Labelled P5-310-2. Rock 3-Small pillow fragment from same location as samples 1 and 2. There is a partly spaled glass surface on one side and a ribbon of glass on the opposite side, but still usable glass is present. Same lithology as samples 1 and 2. Labelled P5-310-3. Rock 4- Thin chip of rock (3x2x0.5 cm) in basket with samples 1 to 3, and presumed to have been collected at same site. No glass present. Sample is more vesicular than samples 1 to 3 and is probably a different lithology. Labelled P5-310-4. Scoop 1- A sediment scoop was collected at the same site as samples 1 to 4. Sample consists of a collection of small, dense, glass fragments (largest about 2-3 cm across), some are fresh and black whereas others have orange nontronite stain. Labelled P5-310-SC1. Basket 1- On recovery, we found a collection of perhaps 30 small (up to cm-sized) fragments of grey rock were found in the front edge of the basket on the starboard side. The fragments are of a highly vesicular lava (50% vesicles) that has been mineralized and coated with amorphous silica (?) and Fe-sulfide. Sulfide is abundant in several fragments and appears to be mainly pyrite. These samples were inadvertently scooped up by the basket during sampling, probably at vent site #5. Probable location: 18 54.513', 155 15.423', depth=1177m. Labelled P5-310-B. Tow-Yo-1 Oct. 2,1996. South-southeast to north-northwest. Cast hit bottom three times. Bottle 7 had glass chips embedded in its side. However, due to the multiple hits, its location cannot be determined. Sample labelled KOK1096-TY-1. Dive P5-311, Oct. 3, 1996. Gary McMurtry, observer. Dive returned to vent 2 site at northeast wall of Pele Pit to collect more water, measure temperature, collect bacterial mats. All samples were collected at vent site #2. Location:18 54.524', 155 15.417', depth=1175m. Rock 1- Medium pillow wedge with little glass on upper surface. Lava is dense and contains abundant plagioclase phenocrysts and rare olivine and black clinopyroxene phenocrysts. Labelled P5-311-1. Rock 2- Medium pillow wedge with original black glassy surface on top surface.. Lithology is the same as rock 1. Labelled P5-311-2. Rock 3- Large pillow wedge with original glass surface on entire upper surface. Glass has thin orange nontronite deposits coating it. Lava is dense with same phenocryst assemblage as rocks 1 and 2, but phenocrysts are smaller and less abundant. Labelled P5-311-3. Scoop 1- Two baggies full of rock and glass fragments. Most appear to be the same plagioclase rich lithology. Many of the fragments are as large as 2-3 cm across. Labelled P5-311-Sc1. Basket 1- About 10 small fragments were caught in the front of the basket. These are similar in lithology to rocks 1 to 3, and scoop 1 and presumably came from the same location. A larger pillow fragment was also found on the port skid. It is dense and aphyric and heavily stained with orange nontronite. It is probably from same site, but is talus fom upslope. Labelled P5-311-B. Dive P5-312, Oct. 4, 1996. Dave Clague, observer. This dive began at 1465 m depth along the south rift zone and terminated at 1250 m depth at Kapo Vent on south rift zone. Rock 1- Large hollow pillow fragment with lots of glass on uper surface, but nontronite/oxide deposits both top and bottom.Sample contains small phenocrysts of plagioclase, olivine, and clinopyroxene and has about 5% round vesicles. Location: 18 53.047', 155 15.173', depth=1465m. Rock 2- Small hollow pillow rind with original, but thin glass rind on entire upper surface. Sample has heavy nontronite/oxide staining on top and bottom. Sample contains several percent olivine phenocrysts and 2-3% small round vesicles. Location: 18 53.053', 155 15.181', depth=1466m. Rock 3- Medium hollow pillow fragment with glassy top surface and drip-surface on bottom. Glassy surface has nontronite/oxide deposits that are darker than those on samples 1 an 2. The lava is olivine-phyric with about 5% crystals, and is also highly vesicular with 30% small to large (5 mm) vesicles. Location: 18 53.202', 155 15.220', depth=1374m. The glassy rin is crumbly and about 3 mm thick. Rock 4- Large pillow wedge of vesicular lava. The upper original glass rind is friable, about 3 mm thick, and covered with nontronite/oxide deposits. The sample contains rare small plagioclase crystals and about 30-40% irregularly shaped vesicles. Location: 18 53.303', 155 15.252', depth=1344m. Rock 5- Medium pillow wedge with original glass on upper surface. The glass is vesicular, friable, and coated with dark nontronite/oxides. All surfaces have the nontronite coating so it hard to estimate crystal content, but there is several percent olivine up to 3 mm size. The vesicles are sub-mm sized and generally round. This sample is from Kapo Vents. Location: 18 53.830', 155 15.386', depth=1250m. Scoop 1- Contains abundant limu-like fragments of glass. There appear to be two differnt ages of limu present as some fragments have altered whereas others appear perfectly fresh. There are also rare Pele's hair fragments, angular dense and vesicular glass fragments, and altered lava fragments. Location 18 53.053', 155 15.181', depth=1461m. Slurp 1- Angular glass fragments and some limu-like fragments. Location: 18 53.202', 155 15.220', depth=1374m. Slurp 2- Fine fresh, black dense glass sand/silt. There are some, but not many, limu fragments. Sample is from Naha hydrothermal vents. Location: 18 53.476', 155 15.266', depth=1324m. Slurp 3-Fine sand consisting of angular, dense glass fragments and rare olivine crystals. There are none of the flat glas bubble wall fragments present. The glass fragments do not appear to be as vesicular as the pillow wedge recovered from the same location. Location: 18 53.830', 155 15.386', depth=1250m. Tow-Yo-4, Oct.4, 1996. Tow-yo run from west-southwest to east-northeast across the summit. The cast hit bottom once on the west-southwest upper wall of Pele Pit and collected a 1 cm glass chip embedded in a bottle and three small chips recovered from the lead weights at the base. The larger chip from the bottle is fresh, aphyric, and dense, whereas the three smaller chips are vesicular, and less glassy. Estimated location is 18 54.42', 155 15.48', depth=1320m. The samples are labelled KOK1096-TY-4. Dive P5-313, Oct. 5, 1996. Geoff Wheat, observer. This dive returned to the hydrothermal vents found on the previous dive and mainly sampled water. Rock 1-A small fragment of hollow pillow or sheet-flow crust with good dense glass coated by thick nontronite deposits. The lava contains 2% olivine and 2-3% small round vesicles and a few larger flattened vesicles. Location: Rock 2- A medium-sized contorted, folded sheet-flow fragment of dense, glassy lava. Nontronite covers one surface. The sample contains a few percent olivine in glass that has a few percent vesicles that are small and round. The sample is mostly glass. Same location and same lithology as rock 1. Location Slurp 6- Most of this sample was of bacterial mats slurped from a hydrothermal vent. There was also a small amount of black glass sand recovered that is labelled P5-313-SL6. These chips could be from the flow represented by rocks 1 and 2 or they could be part of the black sand deposts that blanket the area. Location: Dive P5-314, 10/7/96, Max Cremer is observer Dive retunred to vent 2 in the new pit to recover the temperature recorder and to collect bacterial mats. The dive then moved upslope and discovered a field of diffuse flow through nontronite. It then moved along the northwest rim of the pit and out to the west scarp in search of some vents located previously along the west flank of Loihi. These vents were found, but were of low flow rate and on near-vertical slope. Scoop 1: A scoop was collected in nontronite on the west upper flank of Loihi, just north of the spillway from the new pit. The sample was washed and decanted. Two samples were retained: bag 1 contains three pieces of the crust on the nontronite and bag 2 contains the washed sand and silt from the sample. The sand consists of small aggregates of clay and fresh glass fragments. The glass fragments are dense and angular and appear to be spalled glass rinds from pillow lavas. Location: 18 54.490', 155 15.890', Depth:1249 m Basket: Two samples of weathered lava were recovered from the basket. These were apparently picked up either at vent site 2 or from the west flank. Neither has but the thinnest trace of residual glassy surface and both are plagioclase-phyric, similar to the samples from vent 2. Probably location: 18 54.552', 155 15.413', Probable depth:1172m. Dive P5-315, 10/8/96 Nathan Becker, observer. This dive explored the south rift zone between Kapo's vents and the new pit. Three sand scoops were collected to define the distribution and origin of the sand deposits. Scoop 1: Sample is mostly nontronite (washed away), black silt and sand of glass fragments. Glass includes some limu-like fragments and some gravel sized glass fragments. Location: 18 53.875', 155 15.387', Depth:1276m. Scoop 2: Sample is fine black sand and silt of black sand. Limu-like glass sheets are present. Location: 18 54.109', 155 15.298', Depth: 1207m. Scoop 3: Sample is fine black sand and silt mixed with vesicular lava fragments from underlying flow. Location: 18 54.171', 155 15.455', Depth:1143m. Dive P5-316, 10/9/96 Goeff Wheat, observer. This dive returned to the new pit and vent sites 2 and 5. Main objective was to collect more water samples. Rock 1: talus fragment from vent 2 area, nontronite covered pillow wedge, no glass. Location: 18 54.513', 155 15.439', Depth: 1170m. Rock 2: talus fragment from vent 2 area, nontronite covered pillow wedge, no glass. 18 54.513', 155 15.439', Depth: 1170m. Rock 3: fragment of sparkly lava from vent 5. Sample has abundant pyrite crystals on all surfaces. One cavity also has grey phase that may be sphalerite. Location: 18 54.20', 155 15.447', Depth: 1176m. Scoop 1: Collected in talus chute near vent 5. Mostly glassy fragments, but some small sulfide fragments are present. Sample has strong sulfur smell. Location: 18 54.20', 155 15.447', Depth: 1176m. Scoop 2: Collected in vent 5 area. Mostly glassy fragments, but some small sulfide fragments are present. Sample has strong sulfur smell. Location: 18 54.20', 155 15.447', Depth: 1176m. Scoop 3: Collected in talus chute near vent 5. Mostly glass fragments and crstalline rock fragments. Faint sulfur smell, but no sulfide fragments found. Location: 18 54.20', 155 15.447', Depth: 1176m. Basket 1: A cm sized rock chip was lodged in the LaBomba water sampler. It appears to be talus from vent 2. Skid Sample :A single sample of lithified nontronite with embedded glass fragments was recovered from the interior of the skid. It was on top of a bunch of stuff from many dives. The sample is clearly from Loihi and was preserved because the fresh glass is highly vesicular and could be a sample of strongly alkalic lava. It is labelled "Loihi someplace", and its location is unknown.
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Ken Rubin©,
krubin@soest.hawaii.edu
Other credits for this web site.
Last page update on 22 Jul 1998
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