Delta | River System, Sediment Deposition & Land Formation

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</span> </div> </figcaption> </figure> </div><div class="topic-header"> <div class="d-flex align-items-top justify-content-between"> <div class="d-flex flex-column"> <div> <div> <h1>delta</h1></div> </div> <div class="topic-identifier font-16 font-md-20">river system component</div> </div> </div> <div class="d-none d-sm-flex flex-row"> <div class="mr-10 mb-15"> <button class="ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400"> Ask the Chatbot a Question </button> </div> <div class="d-none d-sm-block md-topic-tools qa-action-buttons mb-15" data-topic-id="156797"> <button class="js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2" > <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="more_vert"></em> More Actions </button> <div class="md-more-popover popover popover-sm p-0 font-14 z-1"> <div> <a class="js-modal btn btn-sm btn-link gtm-topic-tool font-weight-bold btn-link" href="/print/article/156797" target="_blank" > <em 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <a class="byline-edit-history" href="https://www.britannica.com/science/delta-river-system-component/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/braid-delta" topicid="77241">braid delta</a></dd> <dd><a href="/science/topset-bed" topicid="599739">topset bed</a></dd> <dd><a href="/science/high-destructive-delta" topicid="265192">high-destructive delta</a></dd> <dd><a href="/science/high-constructive-delta" topicid="265141">high-constructive delta</a></dd> <dd><a href="/science/fan-delta" topicid="201435">fan delta</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/delta-river-system-component"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref277408"></span>delta</strong>, low-lying plain that is composed of stream-borne sediments deposited by a river at its mouth.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">A brief <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="treatment" href="https://www.britannica.com/dictionary/treatment" data-type="EB">treatment</a> of deltas follows. For full treatment, <em>see</em> <a href="https://www.britannica.com/science/river/Economic-significance#ref29117" class="md-crosslink " data-show-preview="true">river: Deltas</a>.</p><span class="marker MOD2 mod-inline"></span><span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">One of the first texts to describe deltas was <em><span id="ref1256339"></span><a href="https://www.britannica.com/topic/History-by-Herodotus" class="md-crosslink ">History</a></em>, written during the 5th century <span class="text-smallcaps">bce</span> by Greek historian <span id="ref173035"></span><a href="https://www.britannica.com/biography/Herodotus-Greek-historian" class="md-crosslink " data-show-preview="true">Herodotus</a>. In that work, Herodotus mentioned that the <a href="https://www.britannica.com/topic/Ionian" class="md-crosslink " data-show-preview="true">Ionian</a> people used the term <em>delta</em> to describe the low-lying region of the <a href="https://www.britannica.com/place/Nile-River" class="md-crosslink " data-show-preview="true">Nile River </a> in Egypt. During a visit to the region, Herodotus also recognized that the land bounded by the seaward-diverging distributary branches of the Nile and the sea was deltoid in shape; he is often given credit for first using the Greek letter 螖 (delta) to describe it. Although many of the world鈥檚 deltas are deltoid, or triangular, in shape, notable exceptions exist. In most cases, the delta shape is controlled by the outline of the water body being filled by sediments. For this reason, the term delta is now normally applied, without reference to shape, to the exposed and submerged plain formed by a river at its mouth.</p><a class="link-module shadow-sm d-block qa-read-more-module" href="/science/river/Economic-significance#ref399665" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/87/187-050-D8600B56/Feluccas-Nile-River-Luxor-Upper-Egypt.jpg" alt="Luxor, Egypt: feluccas on Nile River" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-navy-dark">More From Britannica</div> <div class="font-weight-semi-bold mt-5">river: Deltas</div> </div> </a><span class="marker MOD3 mod-inline"></span><span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Deltas have been important to humankind since prehistoric times. Sands, silts, and clays deposited by floodwaters were extremely productive agriculturally; and major civilizations flourished in the deltaic plains of the Nile and Tigris-Euphrates rivers. In recent years geologists have discovered that much of the world鈥檚 petroleum resources are found in ancient deltaic rocks.</p><span class="marker MOD4 mod-inline"></span><span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">Deltas display much variation in size, structure, <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="composition" href="https://www.merriam-webster.com/dictionary/composition" data-type="MW">composition</a>, and origin. These differences result from sediment <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="deposition" href="https://www.merriam-webster.com/dictionary/deposition" data-type="MW">deposition</a> taking place in a wide range of settings. Numerous factors influence the character of a delta, the most important of which are: climatic conditions, geologic setting and sediment sources in the <a href="https://www.britannica.com/science/drainage-basin" class="md-crosslink autoxref " data-show-preview="true">drainage basin</a>, tectonic stability, river <a href="https://www.britannica.com/science/slope-mathematics" class="md-crosslink autoxref " data-show-preview="true">slope</a> and flooding characteristics, intensities of depositional and erosional processes, and tidal range and offshore energy conditions. Combinations of these factors and time give rise to the wide variety of modern deltas. The presence of a delta represents the continuing ability of rivers to deposit stream-borne sediments more rapidly than they can be removed by waves and <a href="https://www.britannica.com/science/ocean" class="md-crosslink autoxref " data-show-preview="true">ocean</a> currents. Deltas typically consist of three components. The most landward section is called the <span id="ref173036"></span><a href="https://www.britannica.com/science/upper-delta-plain" class="md-crosslink ">upper delta plain</a>, the middle one the <span id="ref173037"></span><a href="https://www.britannica.com/science/lower-delta-plain" class="md-crosslink ">lower delta plain</a>, and the third the <span id="ref173038"></span><a href="https://www.britannica.com/science/subaqueous-delta-plain" class="md-crosslink ">subaqueous delta</a>, which lies seaward of the shoreline and forms below <a href="https://www.britannica.com/science/sea-level" class="md-crosslink autoxref " data-show-preview="true">sea level</a>.</p><div class="one-good-fact-module"> </div><span class="marker MOD5 mod-inline"></span><span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">That part of the river confined by valley walls, termed the <span id="ref173039"></span><a href="https://www.britannica.com/science/floodplain" class="md-crosslink " data-show-preview="true">alluvial plain</a>, serves as a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="conduit" href="https://www.merriam-webster.com/dictionary/conduit" data-type="MW">conduit</a> through which sediment and water derived from the drainage basin are brought to the sea. At some point downstream the plain broadens out, and most river channels break up into more than one course. This is the apex of the delta and the beginning of the upper delta plain. All of this land lies at an elevation above the effective intrusion of tidal water and is formed entirely by riverine processes. Areas between channels usually support broad freshwater marshes, swamps, or shallow lakes. The lower delta plain is periodically flooded by tidal waters, and landforms result from the interaction of both riverine and marine processes. Areas between the channels show a variety of landforms, ranging from brackish water bays and <a href="https://www.britannica.com/plant/mangrove" class="md-crosslink autoxref " data-show-preview="true">mangrove</a> swamps to saline tidal flats and <a href="https://www.britannica.com/science/beach" class="md-crosslink autoxref " data-show-preview="true">beach</a> ridges. The subaqueous delta forms entirely below the level of the sea and commonly <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="constitutes" href="https://www.merriam-webster.com/dictionary/constitutes" data-type="MW">constitutes</a> the obvious bulge on the <a href="https://www.britannica.com/science/continental-shelf" class="md-crosslink autoxref " data-show-preview="true">continental shelf</a> seen seaward of many deltas. It serves as the submarine platform across which the exposed delta eventually builds. Variations in the proportions of each deltaic component give rise to the different sizes and slopes of the world鈥檚 deltas.</p><span class="marker MOD6 mod-inline"></span></section> <span class="md-signature">This article was most recently revised and updated by <a href="/editor/John-P-Rafferty/6747">John P. 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Delta | River System, Sediment Deposition & Land Formation | Britannica