Present-day formation of pillow lavas under subaerial conditions of Karymskiy Volcano

Download Present-day formation of pillow lavas under subaerial conditions of Karymskiy Volcano

Post on 19-Feb-2017




0 download

Embed Size (px)


<ul><li><p>This article was downloaded by: [New York University]On: 05 October 2014, At: 14:44Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>International Geology ReviewPublication details, including instructions for authors andsubscription information:</p><p>Present-day formation of pillowlavas under subaerial conditions ofKarymskiy VolcanoB.V. Ivanov aa Institute of Volcanology , Siberian Branch , Academy ofSciences of the U.S.S.R.Published online: 20 Sep 2010.</p><p>To cite this article: B.V. Ivanov (1967) Present-day formation of pillow lavas under subaerialconditions of Karymskiy Volcano, International Geology Review, 9:8, 1036-1041, DOI:10.1080/00206816709474818</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information(the Content) contained in the publications on our platform. However, Taylor&amp; Francis, our agents, and our licensors make no representations or warrantieswhatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions andviews of the authors, and are not the views of or endorsed by Taylor &amp; Francis. Theaccuracy of the Content should not be relied upon and should be independentlyverified with primary sources of information. Taylor and Francis shall not be liablefor any losses, actions, claims, proceedings, demands, costs, expenses, damages,and other liabilities whatsoever or howsoever caused arising directly or indirectly inconnection with, in relation to or arising out of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.Terms &amp; Conditions of access and use can be found at</p><p></p></li><li><p>Present-day formation of pillow lavas</p><p>under subaerial conditions of Karymskiy Volcano</p><p>B.V. Ivanov</p><p>Translated by Dorothy B. Vitahand l</p><p>UDC 552.313:550.42:552.11=03.82=20</p><p>ABSTRACT: Gas saturation independent of chemical composition is considered a decisive factor inthe formation of pillow and globular lavas. In this case, flourine as the reagent, reduced the vis-cosity and density of the andesitic-dacitic lava flow. Effervescence or secondary pulsation in thefrontal part of the moving flow, due to reduced pressure, caused some of the lava to become de-tached from the main mass which, traveling ahead of or along the sides of the flow, acquired pillowor globular shapes depending on their mass, velocity and distance traveled. --IGR Staff.</p><p>* * *</p><p>Karymskiy Volcano, situated northwest ofPetropavlovsk, is one of the most active on theKamchatka Peninsula. Since 1952 the volcanohas been in a state of eruption, and in October1962 it entered into a stage of effusive-explosiveactivity. Between October 1962 and March 1963,three lava flows of andesitic-dacitic composition,but of different morphologic habit, ran down itsflanks. With respect to structure, one of theseflows can be assigned to the so-called pillow orglobular lavas, i. e., those with discrete spher-ical or ellipsoidal masses, each constituting anindependent body with its own cooling surface.This flow poured down the west and northwestflanks of the cone, covering an area of about0.6 km2. Its distribution on the cone was un-even. As a rule the lava filled lows in the re-lief. There is none of it on the upper and middleparts of the cone itself; it is found mainly on agently sloping section near the base of the cone..Somewhat lower down there was another smallflow 150 x 200 m in area, detached from themain one. The main elements of the flow arepillows, transverse rolls, rafted blocks of flowcrust, spheroidal bodies, nearly globular forms,and globules. The distribution of these formsis irregular. The transverse rolls and blocksof flow crust mainly make up the central part ofthe flow; the pillows, globules, ellipsoidalbodies, and nearly spherical forms as a rulemake up the frontal part of the flow, where eachform is an individual body with its own coolingsurface (fig. 1). In certain places the trans-verse rolls and flow crust blocks could be ob-served to overlap the pillows.</p><p>The size of the pillows is very variable,</p><p>from 2-3 to 10 m in diameter (averaging 3-5 m)with a height of not more than 1.5-2.0 m. Typ-ical globules and nearly spherical forms arerare and do not exceed 1.0-1.5 mm diameter.It should be noted that in most cases the typicalglobular forms are those nearest the front ofthe flow.</p><p>The pillow and ellipsoidal forms were ob-served to be asymmetrical in structure; someof them were pear-shaped, the bulging sideturned clovvnslope that is, in the direction offlow (fig. 2). In places where pillows lie oneon top of the other their tops are indented,showing that the material was plastic when thepillows were formed.</p><p>The surface of the pillows and globular for-mations is smooth, glassy, sometimes cracked,slightly bumpy. The glassy crust is absent onthe lower surface of the pillows and globuleswhere they touch the ground and also where theylie one on top of the other. Very often thepillows or globules are radially or concentricallycracked.</p><p>An interesting feature of the pillows and in-dividual globules is the presence of gas cavitiesin their center. These are very variable insize, depending on the size of the pillows orglobules. In some there are round holes 15-20 cm in diameter leading from the hollow cen-ter to the surface. At the time the lava flowwas visited, almost a month and a half after itseruption, the temperature in the center of thepillows, measured through such holes, was180-220C. By then, pyroclastic material hadsifted through the holes into some of the pillows,and a year later all the globular forms withoutlets were filled with pyroclastic materialfrom subsequent explosions.</p><p>The presence of the central cavity and as-sociated holes can be explained by the burstingaction of the gases originally contained in theglobules and pillows. In cases where the pres-sure of the gases was greater than atmosphericpressure they blasted out part of the still-plasticrock mass and formed a hole.</p><p>Translated from Sovremennoye obrazovaniye podush-chnykh lay v subaerial'nykh usloviyakh na Karymskomvulkane, in "Sovremennyy Vulkanizm" : Trudy VtorogoVsesoyuznogo Vulkanologicheskogo Soveshchaniya,3 - 17 sentya.brya 1964, V. 1, p. 49 -55. Moscow, Akad.Nauk Sibirskoye Otdeleniye, Inst. Vulkanologii. Theauthor is with the Institute of Volcanology, SiberianBranch, Academy of Sciences of the U.S.S.R.</p><p>'U.S. Geological Survey (Bloomington, Indiana).Translation published by permission of the Director,U.S. Geological Survey. The space between the pillows on the lava</p><p>Internat. Geology Rev. v.9, no .8</p><p>1036</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>New</p><p> Yor</p><p>k U</p><p>nive</p><p>rsity</p><p>] at</p><p> 14:</p><p>44 0</p><p>5 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>B.V. IVANOV</p><p>FIGURE 1. General view of pillow lava flow on west flank ofKarymskiy volcano. Photo by B.V. lvanov.</p><p>1037</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>New</p><p> Yor</p><p>k U</p><p>nive</p><p>rsity</p><p>] at</p><p> 14:</p><p>44 0</p><p>5 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>. -2. Typical"PiA1,0%.".." in frontal part of flow. .Convex side of "p illow"</p><p>faceS'directfOn'of' lava movement. Photo by B.V. IvancivFIGURE</p><p>INTERNATIONAL GEOLOGY REVIEW</p><p>flow was filled with pyroclastic material, ash,fragments of volcanic bombs and lava; thethickness of the pyroclastic material was 0.5-1.0 m. A study of the pillow and globular formsshowed that three types of cross-sections couldbe distinguished (fig. 3; I, II, III):</p><p>I - Pillows, spheroids, and similar forms with</p><p>central gas cavity .</p><p>- /I - Pillows globules, spheroids, and simi-lar forms without central gas cavity.</p><p>III - Transverse rolls, rafted blocks, oblatebodies, pillows, lying on top of each other, withand without central cavities.</p><p>FIGURE 3. The three types of pillow lava sections</p><p>1 - "chilled" crust;</p><p>2 - "finely vesicular" glassy rock (yes3 - "finely vesicular" main mass (vesic4 - "moderately and coarsely vesicular"5 - streaks and "lenses" of "moderately6 - dense rock, crystallized out to a d7 - cracks.</p><p>icles 1-2 mm in diameter);</p><p>le diameter more than 5 mm);rock (vesicle diameter 5-10 and up to 15 mm);</p><p>and coarsely vesicular" rock;ifferent degree;</p><p>1038</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>New</p><p> Yor</p><p>k U</p><p>nive</p><p>rsity</p><p>] at</p><p> 14:</p><p>44 0</p><p>5 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>B.V. IVANOV</p><p>In a cross section of the first type, four zonescan be distinguished macroscopically from pe-riphery to center: 1) an outer "chilled" crust upto 1 cm thick. This is a glassy, cracked, lightgray rock; 2) finely vesicular, dense glassy rockwith a great number of plagioclase phenocrystsup to 1-2 mm in size. The number of vesiclesis not great. The vesicles are oriented parallelto the surface of the globule or pillow. zoneis not always observed; 3) finely vesicular (ves-icle diameter 2-5 mm) dark gray to gray rock,slightly crystallized out, with plagioclase pheno-crysts up to 1.0-1.5 mm in size. The apparentthickness of this zone is 10-15 cm. The finelyvesicular zone grades into 4) a moderately andcoarsely vesicular zone with vesicles 5-10 mmand more in size, but not coarser than 1.5-2.0 cm. Plagioclase phenocrysts are fewer than inthe finely vesicular zone, and they are not morethan 1 mm in size. Sometimes a faint zonationis suggested by an alternation of places withcoarse and medium vesicles.</p><p>It should be noted that the vesicles are smallat the edge of a gas cavity, the rock there beingreminiscent in texture of a curdy mass, unlikethe pumiceous texture of the interior of volcanicbombs where coarse vesicles (5-10 cm') areseparated by very thin partitions. The zone isup to 15 cm thick.</p><p>In a section of the second type there are dis-tinguished: 1) a "chilled" crust 1.0-1.5 cmthick; 2) a finely vesicular glassy mass witha large number of plagioclase phenocrysts upto 3-5 mm in size. The rock is dark gray incolor, crystallized out to a considerable degree.Finely vesicular spots alternate with dense,glassy rock, almost completely crystallizedout. No zonation can be distinguished, althoughit should be noted that in general, no denseglassy spots are observed in the center of theseglobules and pillows.</p><p>A typical feature of this section is bandingcaused by frequent alternation of the vesicularand dense varieties of rock. The vesicularspots are largely lenslike in shape, while the"crystallized out" mass has no clearly definedshape. Sections of this type are observed intypical globules and in some pillows.</p><p>The third type of section shows two zones:1) a "chilled" crust 1-1.5 cm thick; 2) a darkgray, almost black, finely and moderatelyvesicular mass. The vesicles are from 1 to3.5 mm in diameter. Sometimes there is acentral cavity in the pillows (usually in thelower ones). Banding is frequently noted inthis zone - an alternation of layers of finelyand moderately vesicular rock.</p><p>It is typical of all sections that the finely</p><p>2 Apparently misprint for min. - -Transl .</p><p>vesicular rock plays the role of the "main mass"in which, in most cases, there are no orienta-tions with respect to the surface of the globuleor pillow. In this "main mass" the moderatelyand coarsely vesicular rocks form layers,lenses, and local swirls, mainly parallel to thesurface of the globule.</p><p>A feature common to all sections is the factthat denser material, crystallized out to a dif-ferent degree, is found in the peripheral zoneof the globule or pillow, usually right below the"chilled" crust; there, there are always a largenumber of well formed plagioclase phenocrysts.</p><p>Chemical analysis (I. M. Bender, analyst) ofthe finely vesicular mass (sample 102) gave thefollowing results (in %): Si02 - 61.14; TiO2 -1.30; Al203 - 16.09; Fe203 - 2.62; FeO -3.99; MnO -0.15; MgO - 1.71; CaO -6.75;Na20 -4.67; K20 -1.85; H20+_ 6.17; H20 - -0.12; total - 100.56.</p><p>Preliminary study of the rock under the mi-croscope showed that it is an andesite-dacite,consisting of phenocrysts of plagioclase andorthorhombic and monoclinic pyroxene (15-20%)in a glassy groundmass with distinct flow struc-ture.</p><p>Thus all the facts leave no doubt that it wasa highly fluid lava. The high vesicularity of therock, textural differentiation, and presence ofcentral gas cavities indicate an exceptionallygas-rich lava. The large number of fumaroleson the flow testifies to this. In this particularinstance it seems to us that the gas saturationwas the main factor that made it possible for apillow lava to arise. The snow cover undoubt-edly influenced the formation of the perfectlyround forms to a certain extent, but this prob-ably was not the main factor. The followingfact is not without interest: in May 1963 a fluidflow of andesitic-dacitic composition (62.02%Si02) poured down the snow-covered southwestflank of Karymskiy Volcano. The flow was less gas -rich, as manifested by the smaller number offumaroles on the flow, by the lower vesicularityof the rock, by the lesser degree of crystallinity,and so forth. The flow formed a wavy sheetwith weakly manifested transverse rolls in thefrontal part. No globular or pillow lavas at allwere observed in connection with that flow.Many geologists doubt that it is possible forpillow or globular lavas to form under subaerialconditions, although the possibility of theirorigin under favorable conditions is not ruledout theoretically. It is thought that only thepresence of water permits the maximum mani-festation of surface tension forces. It seemsto us that this point of view is absolutely correctwith respect to the formation of globular lavasof basic composition, and the overwhelmingmajority of such lavas obviously are so formed.Lavas of acid andesitic-dacitic composition areanother matter. The fact that lavas of such</p><p>1039</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>New</p><p> Yor</p><p>k U</p><p>nive</p><p>rsity</p><p>] at</p><p> 14:</p><p>44 0</p><p>5 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>INTERNATIONAL GEOLOGY REVIEW</p><p>composition yield fluid flows is interesting initself, and it is explained, in this case, 'only bytheir exceptional gas saturation. The gas satura-tion affects the physical properties of the lava,reducing its viscosity and maintaining a consider-able temperature for some time, during whichthe lava remains fluid. (More than 1.5 monthsafter the eruption the temperature of the flow inthe spaces between globules, filled with pyro-elastic material, was 570C at a depth of 15 cm;viscous flows not saturated with gases cool con-siderably faster.)</p><p>The composition of the gases also affects theviscosity. The composition of the fumarolegases on the pillow lava flow showed a highfluorine content (up to 70 mg...</p></li></ul>