Sand+Dunes



Sand Dunes Sandy deserts contain enormous volumes of sand eroded from mountains and carried to the deserts by wind or water. The <range type="comment" id="565568925_9">huge </range id="565568925_9"><range type="comment" id="565568925_10">quantities </range id="565568925_10">of sand that <range type="comment" id="565568925_11">make up</range id="565568925_11"> sandy deserts <range type="comment" id="565568925_12">are blown about into</range id="565568925_12"> dunes of <range type="comment" id="565568925_13">various shapes</range id="565568925_13">. Ridge dunes form where there are <range type="comment" id="565568925_14">large amounts</range id="565568925_14"> of sand, generally in the <range type="comment" id="565568925_15">interiors </range id="565568925_15">of deserts, and<range type="comment" id="565568925_16"> winds blow in one direction</range id="565568925_16">. <range type="comment" id="565568925_17">Under </range id="565568925_17">these <range type="comment" id="565568925_18">conditions</range id="565568925_18">, parallel <range type="comment" id="565568925_19">ridges </range id="565568925_19">of sand, known as <range type="comment" id="565568925_20">transverse </range id="565568925_20">dunes, form at right <range type="comment" id="565568925_21">angles</range id="565568925_21"> to the wind. When t<range type="comment" id="565568925_22">he direction of the wind</range id="565568925_22"> changes so that it comes from <range type="comment" id="565568925_23">different </range id="565568925_23"><range type="comment" id="565568925_24">directions</range id="565568925_24">, <range type="comment" id="565568925_25">star-shaped dunes</range id="565568925_25"> form from the <range type="comment" id="565568925_26">massive </range id="565568925_26">amounts of sand in desert interiors. Star-shaped dunes are <range type="comment" id="565568925_27">relatively </range id="565568925_27"><range type="comment" id="565568925_28">stable </range id="565568925_28">dunes that <range type="comment" id="565568925_29">reach </range id="565568925_29"><range type="comment" id="565568925_30">incredible </range id="565568925_30"><range type="comment" id="565568925_31">heights</range id="565568925_31">, up to 80 meters high in some deserts, and are <range type="comment" id="565568925_32">quite common</range id="565568925_32"> in <range type="comment" id="565568925_33">massive </range id="565568925_33">deserts such as the Sahara. <range type="comment" id="565568925_34">Crescent </range id="565568925_34">dunes form on the <range type="comment" id="565568925_35">edges </range id="565568925_35">of deserts where there is <range type="comment" id="565568925_36">less </range id="565568925_36">sand and where the winds blow <range type="comment" id="565568925_37">mainly </range id="565568925_37">in one direction. These dunes, which are also known as <range type="comment" id="565568925_38">barchan dunes</range id="565568925_38">, are less stable than star-shaped dunes and can <range type="comment" id="565568925_39">shift </range id="565568925_39">as much as 20 meters per year as winds blow over the <range type="comment" id="565568925_40">outer </range id="565568925_40"><range type="comment" id="565568925_41">curves </range id="565568925_41">of the <range type="comment" id="565568925_42">crescent </range id="565568925_42">in the direction of the <range type="comment" id="565568925_43">pointed ends.</range id="565568925_43">



ridge 4, 6 star shaped 3 crescent 2,7