Effusive Volcanism

StudyBlue printing of Effusive Volcanism html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td { margin: 0; padding: 0; border: 0; outline: 0; font-size: 100%; background: transparent; } body { line-height: 1; } blockquote, q { quotes: none; } blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; } /* remember to define focus styles! */ :focus { outline: 0; } /* remember to highlight inserts somehow! */ ins { text-decoration: none; } del { text-decoration: line-through; } /* tables still need 'cellspacing="0"' in the markup */ table { border-collapse: collapse; border-spacing: 0; } /* end RESET */ .header { min-width:800px; } .logo { padding:6px 20px 2px 20px; margin:0; font-size:25px; font-weight:bold; 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-moz-border-radius: 5px; -webkit-border-radius: 5px; } .print-button a:hover { background-color:black; } .theNote .content { width: 8.0in !important; margin: 5px auto; padding:20px; background-color:white; } .theNote .header { border-bottom: 1px dashed #C8C8C8; font-size: 17px; padding: 0 0 10px; line-height: 19px; color: #00ADE1; min-width:500px; } .theNote .body { font-size: 14px; line-height: 19px; padding: 10px 0; } .theNote{ padding:6px 0; clear:both; background-color: rgb(200,200,200); } .theNote h3{ color: rgb(100,100,100); } .theNote h1, .theNote h3{ background-color:white; padding:2px 20px; width:8.0in !important; margin: 0 auto; font-size: 15px; } .theNote h1{ padding-top: 10px; font-size: 15px; } .theNote h1:first-child{ font-size: 20px; } .theNote h3 { font-size: 14px; font-weight: normal; } #options { border: 3px double #ccc; padding: 5px 12px; margin: 10px 50px 10px 20px; float: left; } #info { border-top: 1px solid #ccc; padding-top: 5px; font-style: italic; } li { margin: 5px 10px 5px 25px; } ul li { list-style: disc; } ol li { list-style: decimal; } img { border: 0; } table { clear: both; width: 100%; border: 1px solid #c5c5c5; border-width: 1px 0; margin: 0; page-break-after: always; } table#page { page-break-after: auto; } td { text-align: center; font-size: 12px; border-bottom: 1px dashed #c5c5c5; height: 1.75in; width: 50%; padding-left: 15px; } .leftside { border-right: 1px solid #cccccc; padding: 0 15px 0 0; } .bottom td { border-bottom: none; } .clearfix { clear:both; line-height:1px; height:1px; } img { max-width:80%; max-height:150px; margin:20px; } @media print {.header { display: none; } .content .header{ display:inherit; } table { border: 1px dashed #bbb; border-width: 1px 0; } .theNote{ background-color:white; } } Effusive volcanism includes submarine emergence of lava along rift zones early phases of subglacial volcanism lava flows primary landform- cover 70% of earth's oceans volume: Laki, Iceland 1783- covered 565 km^2, 10^15 km^3; Roza Member, Columbia River basalt >1500 km^3 durations: range from days to months Lava flow geometry and morphology - dependent on: physical properties of lava effusion rate- low rates promote pahoehoe, higher=aa local eruptive environment (slope, topography, presence/absence of water) aspect ratio = V/H= thickness/diameter -basaltic flows <1/100 (low) as lava flows away from vent, it crystallizes flows begin to form channels or tubes Pahoehoe characterized by smooth and continuous; elastically stretched surfaces associated with low viscosity lava individual flow sheets are 10's of cm thick advances by- extrusion of lava "toes", inflation of flow interior by arrival of new magma morphological (surface) features pressure ridges- transverse to direction of flow and convex downslope tumuli; squeeze-ups, hornitos tree molds columnar jointing and flow interiors contraction during cooling produces columns tensional stress release perfect hexagons arise from most energetically favorable release of stress 2 or 3 tiered arrangement of columns at base heat is conducted slowly into underlying surface cooling front (defined by "isotherms") migrate slowly upward into flow interior fractures propagate perpendicularly to isotherms thick regular columns form the "lower colonnade"- 1/3 heat loss at surface is rapid- produces thinner, more chaotic columns- "entablature" "upper colonnade"- sometimes present- consists of thick but relatively irregular columns right way up, concave up u pahoehoe is characterized by abundant spherical vesicles- spherical=after flow came to rest? Aa flows chemically and mineralogically, pahoehoe and aa are identical drivers of transition from pahoehoe to aa cooling, gas loss, increase crystallinity high strain rates play major role- higher effusion rates, greater flow velocities Aa interiors contain basal breccia massive interior- some blocky joints capping breccia irregular, less abundant vesicles, formed before cooling ended, expanding into more viscous media- can't be spherical Blocky Lavas common among more viscous lavas with higher silica contents >55% surfaces consisting of broken slabs and blocks vesicle poor not laterally extensive compared to pahoehoe and aa