新月形沙丘的迎风坡和背风坡坡度差别为何很大,这一差异在沙丘内部沉积构造上留下了什么痕迹?
Why do the windward and lee slopes of a barchan dune differ so greatly in steepness, and what imprint does this leave on the dune's internal structure?
迎风坡平缓且较长,气流携带砂粒沿坡爬升;背风坡短而陡,坡度接近干燥砂约34度的天然休止角,构成滑动面。跃移砂粒越过丘顶后在滑动面上堆积,经反复滑塌形成向背风侧倾斜的高角度交错层理。因此古老砂岩中交错层理的倾向可用来恢复沉积时的古风向。
The windward slope is long and gentle because wind-driven sand climbs it grain by grain, whereas the short lee slope rests close to the natural angle of repose of dry sand, about 34 degrees, forming an avalanche slip face. Saltating grains carried over the crest settle on this face, and repeated avalanching builds steeply dipping cross-bedding inclined downwind. The dip direction of such cross-beds preserved in ancient sandstones can therefore be used to reconstruct palaeowind directions.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：作者 / 书名 / 版次 / 出版社 / 年份齐备，仅缺独立比对证据；已在可信度报告单列披露，不再重复核验。
吴正《风沙地貌学》,科学出版社,1987 ; 另见: Pye, K. & Tsoar, H. (2009). Aeolian Sand and Sand Dunes. Berlin: Springer.
Pye, K. & Tsoar, H. (2009). Aeolian Sand and Sand Dunes. Berlin: Springer. ; see also: 吴正《风沙地貌学》,科学出版社,1987
#风沙地貌 #沙丘交错层理
新月形沙丘为什么迎风坡缓、背风坡陡,沙丘前移的速度又由什么决定?
Why does a barchan dune have a gentle windward slope and a steep lee face, and what determines how fast the dune advances?
风沙流把沙粒沿迎风坡向上搬,坡角稳定在约10-15度;越过脊线后沙粒重力崩落,形成接近34度休止角的陡峭落沙坡。沙丘整体顺主导风向前进,移动速率大致与丘高成反比,故小沙丘迁移快、大沙丘迁移慢。植被固沙或水分增加时,流动沙丘可转为半固定状态。
Saltation carries grains up the windward face, which settles near 10-15 degrees; beyond the crest they avalanche under gravity, building a steep brink face close to the 34-degree angle of repose. The whole dune advances downwind at a rate roughly inversely proportional to its height, so small barchans migrate faster than large ones. When vegetation anchors the sand or moisture rises, a mobile dune turns semi-fixed.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-02
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吴正《风沙地貌学》,科学出版社,1987 ; 另见: Bagnold, The Physics of Blown Sand and Desert Dunes, Methuen, 1941
Bagnold, The Physics of Blown Sand and Desert Dunes, Methuen, 1941 ; see also: 吴正《风沙地貌学》,科学出版社,1987
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL1568236W：The physics of blown sa
#风沙地貌 #沙丘动力学
新月形沙丘的两个尖角为什么总是指向风吹去的方向?
Why do the two pointed horns of a barchan dune always point downwind?
在沙源有限、主风向单一的环境里,沙丘形成平缓的迎风坡和保持约34°休止角的背风滑落面。跃移的沙粒被风从迎风坡搬越丘顶,堆落在滑落面上,整座沙丘因此顺风整体前移。两翼沙量少,输沙更快完成,便逐渐拉长为指向下风向的两只尖角,勾出完整的新月形轮廓。
Where sand supply is scarce and one wind direction dominates, a dune builds a gentle windward slope and a lee avalanche face standing at the angle of repose of about 34°. Saltating grains are carried over the crest from the windward flank and settle on the slip face, so the whole dune advances downwind. The flanks hold little sand, so transport clears them faster and they stretch into two horns pointing downwind, tracing out the full crescent shape.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
R. A. Bagnold,《风吹沙与沙漠沙丘物理学》(The Physics of Blown Sand and Desert Dunes),Methuen,1941年
Ralph A. Bagnold, The Physics of Blown Sand and Desert Dunes, Methuen, 1941
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL1568236W：The physics of blown sa
#风成地貌 #新月形沙丘