黃(huang)(huang)土(tu)高(gao)原(yuan)(yuan)地勢西北高(gao),東(dong)南低,自西北向東(dong)南呈波(bo)狀下降(jiang)。以(yi)六盤山(shan)和呂梁山(shan)為(wei)界(jie)把黃(huang)(huang)土(tu)高(gao)原(yuan)(yuan)分為(wei)東(dong)、中(zhong)、西三部分:六盤山(shan)以(yi)西的(de)(de)黃(huang)(huang)土(tu)高(gao)原(yuan)(yuan)西部,海拔(ba)2000-3000米,是(shi)黃(huang)(huang)土(tu)高(gao)原(yuan)(yuan)地勢高(gao)的(de)(de)地區(qu)。
六(liu)盤山與呂梁(liang)山之司的(de)黃(huang)土高原中(zhong)部,海(hai)拔1000-2000米,是黃(huang)土高原的(de)主體。呂梁(liang)山以東的(de)黃(huang)土高原東部,地勢降至500-1000米,河谷平(ping)原占有(you)較大比例。
據此可(ke)將黃(huang)土高(gao)原(yuan)分為山地區(qu)、黃(huang)土丘陵區(qu)、黃(huang)土塬(yuan)區(qu)、黃(huang)土臺塬(yuan)區(qu)、河谷(gu)平(ping)原(yuan)區(qu)。
黃(huang)土高原(yuan)基(ji)巖(yan)構(gou)(gou)造(zao)以(yi)(yi)(yi)六(liu)盤(pan)(pan)山(shan)為(wei)界(jie)分為(wei)東(dong)西(xi)兩部(bu)分,西(xi)部(bu)屬(shu)西(xi)域陸(lu)塊(kuai)(kuai),東(dong)部(bu)屬(shu)華北陸(lu)塊(kuai)(kuai)。六(liu)盤(pan)(pan)山(shan)以(yi)(yi)(yi)西(xi)黃(huang)土高原(yuan)以(yi)(yi)(yi)新(xin)生(sheng)代斷陷盆地(di)(di)為(wei)構(gou)(gou)造(zao)特征,隴中盆地(di)(di)黃(huang)土下(xia)伏基(ji)巖(yan)為(wei)直接堆(dui)積(ji)在古老(lao)巖(yan)層(ceng)之上(shang)的(de)中新(xin)世到上(shang)新(xin)世早期的(de)甘肅群(qun)。甘肅群(qun)堆(dui)積(ji)后,上(shang)新(xin)世晚期地(di)(di)面抬(tai)(tai)升(sheng),黃(huang)河(he)及其(qi)支流挑河(he)、祖(zu)歷河(he)、葫(hu)蘆(lu)河(he)隨抬(tai)(tai)升(sheng)而下(xia)切(qie),基(ji)巖(yan)地(di)(di)面成(cheng)(cheng)為(wei)起伏較(jiao)(jiao)大的(de)丘陵狀。甘肅群(qun)為(wei)一套含有(you)石膏的(de)紫紅色(se)粘土,砂質粘土,砂巖(yan)和(he)(he)砂礫巖(yan)。其(qi)成(cheng)(cheng)巖(yan)性差,抗蝕力較(jiao)(jiao)弱(ruo),在地(di)(di)下(xia)水浸泡和(he)(he)潤滑作用下(xia)極易發生(sheng)重(zhong)力侵蝕,常(chang)形成(cheng)(cheng)大型滑坡。六(liu)盤(pan)(pan)山(shan)以(yi)(yi)(yi)東(dong)的(de)華北陸(lu)臺由鄂爾(er)多斯(si)臺向(xiang)斜(xie)(xie)和(he)(he)山(shan)西(xi)臺背斜(xie)(xie)構(gou)(gou)成(cheng)(cheng),中間夾以(yi)(yi)(yi)黃(huang)河(he)凹陷。鄂爾(er)多斯(si)臺向(xiang)斜(xie)(xie)和(he)(he)山(shan)西(xi)臺背斜(xie)(xie)是未經褶皺(zhou)變動的(de)前震旦紀(ji)陸(lu)臺。
陜北(bei)、隴東(dong)和晉西(xi)的(de)(de)(de)(de)(de)(de)(de)(de)鄂爾(er)多(duo)斯(si)(si)(si)臺(tai)向(xiang)斜(xie)在中(zhong)(zhong)生(sheng)(sheng)(sheng)代發(fa)展成(cheng)(cheng)為(wei)一(yi)(yi)個大(da)型(xing)的(de)(de)(de)(de)(de)(de)(de)(de)內陸盆地(di)(di)(di),當(dang)(dang)時地(di)(di)(di)勢東(dong)南(nan)高(gao)西(xi)北(bei)低,與今況剛(gang)好相反。西(xi)北(bei)部堆(dui)積(ji)了厚達1500米(mi)完整的(de)(de)(de)(de)(de)(de)(de)(de)中(zhong)(zhong)生(sheng)(sheng)(sheng)代地(di)(di)(di)層(ceng)序列。其中(zhong)(zhong)神木(mu),準格爾(er)旗一(yi)(yi)帶(dai)廣泛出露的(de)(de)(de)(de)(de)(de)(de)(de)中(zhong)(zhong)生(sheng)(sheng)(sheng)代灰綠(lv)色(se)、黃(huang)綠(lv)色(se)長石砂(sha)(sha)巖,當(dang)(dang)地(di)(di)(di)叫砒砂(sha)(sha)巖,極易風化侵蝕,是(shi)(shi)當(dang)(dang)地(di)(di)(di)及黃(huang)河中(zhong)(zhong)粗砂(sha)(sha)的(de)(de)(de)(de)(de)(de)(de)(de)主(zhu)要來源。燕(yan)山(shan)(shan)運動使(shi)鄂爾(er)多(duo)斯(si)(si)(si)臺(tai)向(xiang)斜(xie)抬升,邊(bian)緣(yuan)發(fa)生(sheng)(sheng)(sheng)斷陷(xian),形成(cheng)(cheng)汾(fen)渭谷地(di)(di)(di)等(deng)一(yi)(yi)系列地(di)(di)(di)塹(qian)谷地(di)(di)(di),到(dao)第三(san)紀(ji)的(de)(de)(de)(de)(de)(de)(de)(de)中(zhong)(zhong)新(xin)(xin)世(shi)末(mo)鄂爾(er)多(duo)斯(si)(si)(si)臺(tai)向(xiang)斜(xie)成(cheng)(cheng)為(wei)準平原(yuan)(yuan)(yuan)。上(shang)(shang)新(xin)(xin)世(shi)鄂爾(er)多(duo)斯(si)(si)(si)高(gao)原(yuan)(yuan)(yuan)長城以(yi)(yi)南(nan)的(de)(de)(de)(de)(de)(de)(de)(de)準平原(yuan)(yuan)(yuan)面(mian)上(shang)(shang)廣泛堆(dui)積(ji)了三(san)趾(zhi)馬紅(hong)土(tu),從三(san)趾(zhi)馬紅(hong)土(tu)的(de)(de)(de)(de)(de)(de)(de)(de)分布和厚度看,上(shang)(shang)新(xin)(xin)世(shi)時長城以(yi)(yi)南(nan),渭北(bei)北(bei)山(shan)(shan)以(yi)(yi)北(bei),六(liu)盤山(shan)(shan)與呂梁山(shan)(shan)之間是(shi)(shi)一(yi)(yi)個淺凹形的(de)(de)(de)(de)(de)(de)(de)(de)巨(ju)大(da)盆地(di)(di)(di)。地(di)(di)(di)勢西(xi)北(bei)高(gao),東(dong)南(nan)低,己與今相同。三(san)趾(zhi)馬紅(hong)土(tu)透水(shui)性極差(cha),是(shi)(shi)黃(huang)土(tu)下覆的(de)(de)(de)(de)(de)(de)(de)(de)主(zhu)要不透水(shui)層(ceng),而且三(san)趾(zhi)馬紅(hong)土(tu)容(rong)易吸水(shui)膨(peng)脹,是(shi)(shi)黃(huang)土(tu)高(gao)原(yuan)(yuan)(yuan)大(da)型(xing)滑坡的(de)(de)(de)(de)(de)(de)(de)(de)主(zhu)要滑移層(ceng)。上(shang)(shang)新(xin)(xin)世(shi)晚(wan)期到(dao)更新(xin)(xin)世(shi),鄂爾(er)多(duo)斯(si)(si)(si)高(gao)原(yuan)(yuan)(yuan)邊(bian)緣(yuan)如汾(fen)渭地(di)(di)(di)塹(qian)谷地(di)(di)(di)進一(yi)(yi)步發(fa)展,同時高(gao)原(yuan)(yuan)(yuan)整體(ti)發(fa)生(sheng)(sheng)(sheng)掀斜(xie)運動,使(shi)地(di)(di)(di)面(mian)形成(cheng)(cheng)自西(xi)北(bei)向(xiang)東(dong)南(nan)傾斜(xie)的(de)(de)(de)(de)(de)(de)(de)(de)斜(xie)面(mian),控制著河流(liu)的(de)(de)(de)(de)(de)(de)(de)(de)流(liu)向(xiang)。在地(di)(di)(di)貌演(yan)變過程中(zhong)(zhong)溝谷的(de)(de)(de)(de)(de)(de)(de)(de)發(fa)展,谷間地(di)(di)(di)有些(xie)形成(cheng)(cheng)面(mian)積(ji)不大(da)的(de)(de)(de)(de)(de)(de)(de)(de)平臺(tai),有些(xie)成(cheng)(cheng)為(wei)長條狀(zhuang)或橢(tuo)圓狀(zhuang)丘陵,它們(men)是(shi)(shi)鄂爾(er)多(duo)斯(si)(si)(si)高(gao)原(yuan)(yuan)(yuan)塬(yuan)、梁、峁地(di)(di)(di)形的(de)(de)(de)(de)(de)(de)(de)(de)基礎。
山(shan)(shan)(shan)(shan)(shan)西(xi)臺(tai)背(bei)斜(xie)包括太行山(shan)(shan)(shan)(shan)(shan)以西(xi)、呂梁山(shan)(shan)(shan)(shan)(shan)以東(dong)。五(wu)臺(tai)山(shan)(shan)(shan)(shan)(shan)是山(shan)(shan)(shan)(shan)(shan)西(xi)臺(tai)背(bei)斜(xie)古(gu)老的(de)(de)部分,并以此為(wei)頂點向南(nan)沿伸(shen),東(dong)部為(wei)太行山(shan)(shan)(shan)(shan)(shan),西(xi)部為(wei)呂梁山(shan)(shan)(shan)(shan)(shan),兩山(shan)(shan)(shan)(shan)(shan)之間為(wei)凹(ao)陷(xian)部分。古(gu)生代以來,凹(ao)陷(xian)部分堆(dui)積了巨厚(hou)的(de)(de)陸(lu)相(xiang)碎(sui)屑(xie)物。燕山(shan)(shan)(shan)(shan)(shan)運(yun)動后山(shan)(shan)(shan)(shan)(shan)西(xi)臺(tai)背(bei)斜(xie)中(zhong)部受斷(duan)(duan)(duan)裂作(zuo)用(yong)晉(jin)(jin)中(zhong)大斷(duan)(duan)(duan)谷開始形成(cheng)。中(zhong)新世末晉(jin)(jin)中(zhong)南(nan)的(de)(de)漳沁地區形成(cheng)準平原,其后接受了上新世的(de)(de)三趾馬紅(hong)土(tu)堆(dui)積。喜馬拉雅運(yun)動使山(shan)(shan)(shan)(shan)(shan)西(xi)臺(tai)背(bei)斜(xie)進一(yi)步上升(sheng),晉(jin)(jin)中(zhong)斷(duan)(duan)(duan)谷不斷(duan)(duan)(duan)發育(yu),河流下切,到(dao)更新世黃土(tu)堆(dui)積時地面形成(cheng)起伏較大的(de)(de)丘陵(ling)、成(cheng)為(wei)山(shan)(shan)(shan)(shan)(shan)地與斷(duan)(duan)(duan)谷、盆(pen)地相(xiang)間分布(bu)的(de)(de)地形特征。
●黃土地層與黃土分布
黃土高原原生黃土是第四紀冰期干冷氣候條件下的風塵堆積物,次生黃土是原生黃土經洪積、沖積改造而成的。在第四紀黃土堆積時期,隨著冰期、間冰期的氣候旋迥,黃土地層呈現黃土與古土壤的更替變化。根據黃土中的古土壤,黃土地層自下而上可以分為午城黃土、離石黃上、馬蘭黃土和世黃土。按洛川黑木溝黃土剖面,第十五層黃土下界面之下為早更新世午城黃土。古土(tu)(tu)(tu)(tu)壤(rang)上(shang)界(jie)面之下(xia)至第十五層(ceng)黃(huang)土(tu)(tu)(tu)(tu)下(xia)界(jie)面之間(jian)為(wei)中(zhong)(zhong)(zhong)更新離石黃(huang)土(tu)(tu)(tu)(tu)。黃(huang)土(tu)(tu)(tu)(tu)層(ceng)是(shi)(shi)形成于晚更新世(shi)的(de)(de)馬蘭黃(huang)土(tu)(tu)(tu)(tu)。馬蘭黃(huang)土(tu)(tu)(tu)(tu)之上(shang)的(de)(de)黑滬(hu)土(tu)(tu)(tu)(tu)為(wei)形成于古土(tu)(tu)(tu)(tu)壤(rang)層(ceng)。黃(huang)土(tu)(tu)(tu)(tu)高原黃(huang)土(tu)(tu)(tu)(tu)地層(ceng)的(de)(de)分布(bu)厚度(du)(du)(du)在(zai)六(liu)盤山(shan)(shan)與呂梁山(shan)(shan)之間(jian)一(yi)般為(wei)150-250米(mi)(mi)(mi),六(liu)盤山(shan)(shan)以西(xi)一(yi)般在(zai)100米(mi)(mi)(mi)以內。不(bu)同(tong)地層(ceng)黃(huang)土(tu)(tu)(tu)(tu)厚度(du)(du)(du)也(ye)不(bu)相同(tong):午城黃(huang)土(tu)(tu)(tu)(tu)厚度(du)(du)(du)不(bu)大,洛川(chuan)黑木溝為(wei)58米(mi)(mi)(mi),山(shan)(shan)西(xi)午城為(wei)17.5米(mi)(mi)(mi)。離石黃(huang)土(tu)(tu)(tu)(tu)是(shi)(shi)黃(huang)土(tu)(tu)(tu)(tu)高原黃(huang)土(tu)(tu)(tu)(tu)地層(ceng)的(de)(de)主體,一(yi)般厚度(du)(du)(du)100-150米(mi)(mi)(mi),厚度(du)(du)(du)分布(bu)在(zai)徑河與洛河的(de)(de)中(zhong)(zhong)(zhong)游地區。馬蘭黃(huang)土(tu)(tu)(tu)(tu)分布(bu)極為(wei)廣泛,一(yi)般厚度(du)(du)(du)10-30米(mi)(mi)(mi),天水(shui)附近小于10米(mi)(mi)(mi),董志源9.6米(mi)(mi)(mi),洛川(chuan)源10米(mi)(mi)(mi)左右。世(shi)黃(huang)土(tu)(tu)(tu)(tu)厚度(du)(du)(du)-般為(wei)2-3米(mi)(mi)(mi),其中(zhong)(zhong)(zhong)的(de)(de)黑滬(hu)土(tu)(tu)(tu)(tu)層(ceng)厚度(du)(du)(du)1-2米(mi)(mi)(mi)。
●黃土粒度與黃土性質
黃土是在風力吹揚搬運下,在干旱半干旱環境堆積的風成堆積物,經過長距離的搬運和分選,其物質組成具有高度的均一性。黃土粒度以粒徑0.05-0.005毫米的粉砂為主,所占比例58-75%。其次為粒徑>0.05毫米的細砂,占15-32%。粒徑0<0.005毫米的粘土占10%左右。黃土粒徑存在著自西北向東南逐漸變細的特點,這一特點以砂粒和粘粒的變化明顯。北部榆林附近砂粒的重量比在30%以上,向南到清澗、延安附近降為20%左右,咸陽、寶雞一帶降至10%上下。相反,榆林粘粒僅占10%左右,延安、清澗一帶增至13-18%,咸陽、寶雞為23-26%。這樣自西北向東南根據黃土粒徑可以把黃土高原黃土分為砂黃土、典型黃土和粘黃土三個帶:靜樂北-綏德-子長-環縣-海原一線以北為砂黃上帶。陽泉-沁縣-浮山北-淳化-秦安-渭源以北,砂黃土帶以南為典型黃土帶。典型黃土帶以南為粘黃土帶。黃土在南北方向上的粒度分異對黃土地貌及土壤侵蝕具有深刻的影響。
黃土含有60多種礦物(wu),其中石英占(zhan)重量(liang)的50%左(zuo)右,長石占(zhan)20%左(zuo)右,碳酸鈣(gai)占(zhan)10%左(zuo)右。就化(hua)(hua)(hua)學(xue)組成(cheng)而言(yan),以二(er)氧(yang)(yang)化(hua)(hua)(hua)硅占(zhan)優勢(50%),其次為三氧(yang)(yang)化(hua)(hua)(hua)二(er)氯(lv)(8-15%),氧(yang)(yang)化(hua)(hua)(hua)鈣(gai)(10%左(zuo)右),以及三氧(yang)(yang)化(hua)(hua)(hua)二(er)鐵(tie),氧(yang)(yang)化(hua)(hua)(hua)鎂,氧(yang)(yang)化(hua)(hua)(hua)鉀,氧(yang)(yang)化(hua)(hua)(hua)鈉等,黃土中易溶性化(hua)(hua)(hua)學(xue)成(cheng)份含量(liang)較高(gao)。
黃(huang)(huang)(huang)(huang)土(tu)(tu)結(jie)構(gou)為“點、棱接(jie)觸支架(jia)式(shi)多孔(kong)結(jie)構(gou)”,土(tu)(tu)體疏松(song),垂直節理發(fa)育,極(ji)易(yi)滲水(shui)。黃(huang)(huang)(huang)(huang)土(tu)(tu)中(zhong)細粒物質如粘土(tu)(tu)、易(yi)溶性鹽類、石膏、碳酸鹽等(deng)在(zai)干燥時固結(jie)成(cheng)(cheng)聚積體,使黃(huang)(huang)(huang)(huang)土(tu)(tu)具有較(jiao)強的(de)強度,而遇水(shui)后隨著礦(kuang)物溶解(jie)與分散(san),土(tu)(tu)體會迅速(su)分散(san)、崩解(jie)。黃(huang)(huang)(huang)(huang)土(tu)(tu)的(de)抗侵蝕(shi)(shi)能(neng)力很(hen)弱(ruo)。黃(huang)(huang)(huang)(huang)土(tu)(tu)中(zhong)孔(kong)隙度-般可達(da)45-50%,尤其大孔(kong)隙特別(bie)突出,當受水(shui)浸潤后上體在(zai)自重和(he)上部壓力作用下,易(yi)發(fa)生濕陷。同時大孔(kong)隙也成(cheng)(cheng)為土(tu)(tu)體中(zhong)水(shui)體和(he)細粒物質遷移的(de)通(tong)道,使黃(huang)(huang)(huang)(huang)土(tu)(tu)易(yi)發(fa)生潛(qian)蝕(shi)(shi)。
黃土(tu)高(gao)原(yuan)是(shi)新構造(zao)運動(dong)(dong)比(bi)較活躍(yue)的(de)(de)區(qu)域(yu),新構造(zao)運動(dong)(dong)的(de)(de)主(zhu)要(yao)表現(xian)(xian)是(shi)高(gao)原(yuan)內(nei)部間(jian)歇(xie)性的(de)(de)大(da)面積整(zheng)體抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng),同時周(zhou)圍的(de)(de)拗陷區(qu)域(yu)不(bu)斷(duan)地(di)沉降。從(cong)黃土(tu)高(gao)原(yuan)廣大(da)地(di)區(qu)河谷多發(fa)育有3-4級階(jie)地(di)等(deng)判斷(duan),第四紀以(yi)來黃上高(gao)原(yuan)以(yi)抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)為(wei)(wei)主(zhu),抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)幅度在150-30米(mi),地(di)殼抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)有利河流(liu)下切(qie)和侵蝕地(di)貌發(fa)育,也(ye)有利于土(tu)壤侵蝕過程的(de)(de)加強(qiang)。黃土(tu)高(gao)原(yuan)內(nei)部六(liu)盤山(shan)是(shi)新構造(zao)運動(dong)(dong)的(de)(de)抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)中心,據現(xian)(xian)代水(shui)準測量(liang)(liang),目前(qian)的(de)(de)抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)速度為(wei)(wei)20毫米(mi)/年(nian)。六(liu)盤山(shan)以(yi)西(xi)地(di)區(qu)抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)量(liang)(liang)大(da)于以(yi)東地(di)區(qu),抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)在華家(jia)嶺一帶(dai),據1934-1955年(nian)隴海鐵路水(shui)準測量(liang)(liang),隴西(xi)、渭源等(deng)地(di)現(xian)(xian)代抬(tai)(tai)升(sheng)(sheng)(sheng)(sheng)速度為(wei)(wei)31.4毫米(mi)/年(nian),隆(long)德、莊浪一帶(dai)溝(gou)床下切(qie)速率達(da)45-240毫米(mi)/100年(nian)。
華家(jia)嶺(ling)以南地區(qu)河(he)(he)谷(gu)(gu)狹窄,一(yi)(yi)(yi)般有3-4級階地,華家(jia)嶺(ling)以北河(he)(he)谷(gu)(gu)較(jiao)寬闊,只有2-3級階地發育,所以華家(jia)嶺(ling)以南抬(tai)升(sheng)幅度(du)更大。六(liu)盤山(shan)(shan)以東地區(qu)白于山(shan)(shan)至東勝一(yi)(yi)(yi)帶是(shi)新構造運(yun)(yun)動(dong)(dong)(dong)抬(tai)升(sheng)的(de)中心。保德附近現代抬(tai)升(sheng)速(su)度(du)在(zai)3毫米(mi)/年左右。山(shan)(shan)西臺背斜新構造運(yun)(yun)動(dong)(dong)(dong)抬(tai)升(sheng)幅度(du)較(jiao)大在(zai)五(wu)臺山(shan)(shan)-恒山(shan)(shan)一(yi)(yi)(yi)帶,這(zhe)從(cong)五(wu)臺山(shan)(shan)、恒山(shan)(shan)山(shan)(shan)前(qian)發育的(de)串珠狀(zhuang)洪積扇可以得到證明。第四(si)紀黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)在(zai)抬(tai)升(sheng)的(de)同時,邊緣(yuan)拗陷區(qu)如銀川平原(yuan)(yuan)(yuan)、汾渭(wei)(wei)(wei)(wei)谷(gu)(gu)地在(zai)大幅度(du)下沉,渭(wei)(wei)(wei)(wei)河(he)(he)平原(yuan)(yuan)(yuan)固始凹陷第四(si)紀沉積物厚度(du)接(jie)近1000米(mi)。據地形變形資料(liao),汾渭(wei)(wei)(wei)(wei)地塹的(de)下沈速(su)度(du)為3毫米(mi)/年。黃(huang)河(he)(he)自(zi)140萬年前(qian)后沖出三門峽后,汾渭(wei)(wei)(wei)(wei)谷(gu)(gu)地是(shi)黃(huang)河(he)(he)中游眾多支(zhi)流的(de)侵蝕基準(zhun)面(mian)(mian)(mian),一(yi)(yi)(yi)方面(mian)(mian)(mian)黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)不(bu)斷抬(tai)升(sheng),另(ling)一(yi)(yi)(yi)方面(mian)(mian)(mian)汾渭(wei)(wei)(wei)(wei)谷(gu)(gu)地持(chi)續下沉,必然對黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)土(tu)(tu)(tu)壤(rang)侵蝕起促進作用。地震是(shi)黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)新構造運(yun)(yun)動(dong)(dong)(dong)的(de)強烈表(biao)現形式,對歷史(shi)(shi)時期黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)地震記載進行(xing)統計,可以反映出黃(huang)土(tu)(tu)(tu)高(gao)原(yuan)(yuan)(yuan)歷史(shi)(shi)時期新構造運(yun)(yun)動(dong)(dong)(dong)的(de)強弱變化過程。
黃土高(gao)(gao)原(yuan)是中(zhong)華民族的(de)發(fa)祥地(di)(di)(di)之一(yi)(yi)(yi),新石器時(shi)期文化遺址在(zai)黃土高(gao)(gao)原(yuan)南部分布廣泛,尤其(qi)在(zai)汾(fen)渭河谷(gu)地(di)(di)(di)和豫(yu)西(xi)(xi)(xi)地(di)(di)(di)區稠密。當時(shi)人(ren)(ren)們以(yi)漁獵、采集(ji)為生(sheng),說明當時(shi)黃土高(gao)(gao)原(yuan)南部維持著較好(hao)的(de)自然(ran)生(sheng)態系(xi)統(tong)。商周(zhou)(zhou)時(shi)期中(zhong)國(guo)出現(xian)了文字(zi)記載,生(sheng)產力水平(ping)的(de)提高(gao)(gao),農(nong)(nong)(nong)業(ye)(ye)(ye)生(sheng)產由原(yuan)始農(nong)(nong)(nong)業(ye)(ye)(ye)向傳統(tong)農(nong)(nong)(nong)業(ye)(ye)(ye)轉變。商周(zhou)(zhou)時(shi)周(zhou)(zhou)人(ren)(ren)主(zhu)要活動(dong)的(de)北(bei)豳(bin)(慶(qing)陽、西(xi)(xi)(xi)峰一(yi)(yi)(yi)帶(dai))、古豳(bin)(彬縣、長武一(yi)(yi)(yi)帶(dai))、周(zhou)(zhou)原(yuan)(扶風、岐(qi)山一(yi)(yi)(yi)帶(dai))鋤(chu)(chu)耕農(nong)(nong)(nong)業(ye)(ye)(ye)已發(fa)展(zhan)(zhan)到一(yi)(yi)(yi)定水平(ping)。夏(xia)代(dai)中(zhong)國(guo)有人(ren)(ren)口(kou)1355萬,周(zhou)(zhou)代(dai)1371萬人(ren)(ren),其(qi)中(zhong)1/2左右分布在(zai)汾(fen)渭河谷(gu)和豫(yu)西(xi)(xi)(xi)地(di)(di)(di)區,這兩地(di)(di)(di)區人(ren)(ren)口(kou)密度30-40人(ren)(ren)/平(ping)方千米。即便如此(ci),從《詩經》中(zhong)仍(reng)可看到黃土高(gao)(gao)原(yuan)南部野鹿成群(qun),虎豹(bao)出沒,森林面(mian)積廣大,農(nong)(nong)(nong)耕面(mian)積有限。春秋(qiu)、戰(zhan)(zhan)國(guo)時(shi)期鐵(tie)器出現(xian),犁(li)耕農(nong)(nong)(nong)業(ye)(ye)(ye)逐(zhu)漸(jian)代(dai)替(ti)鋤(chu)(chu)耕農(nong)(nong)(nong)業(ye)(ye)(ye),關中(zhong)、汾(fen)河谷(gu)地(di)(di)(di)、洛陽盆地(di)(di)(di)、天(tian)(tian)水盆地(di)(di)(di)農(nong)(nong)(nong)業(ye)(ye)(ye)進一(yi)(yi)(yi)步(bu)發(fa)展(zhan)(zhan)。戰(zhan)(zhan)國(guo)時(shi)秦將自己的(de)勢(shi)力向渭河上游、陜北(bei)北(bei)部推進,趙則向晉北(bei)地(di)(di)(di)區擴張(zhang),在(zai)這些(xie)地(di)(di)(di)區建立城邑,開墾土地(di)(di)(di),發(fa)展(zhan)(zhan)耕作,但直到戰(zhan)(zhan)國(guo)末農(nong)(nong)(nong)耕業(ye)(ye)(ye)主(zhu)要集(ji)中(zhong)在(zai)太原(yuan)一(yi)(yi)(yi)龍門一(yi)(yi)(yi)天(tian)(tian)水以(yi)南地(di)(di)(di)區,以(yi)北(bei)畜(chu)牧(mu)業(ye)(ye)(ye)仍(reng)占(zhan)優勢(shi),整個黃土高(gao)(gao)原(yuan)人(ren)(ren)口(kou)少(shao),開墾指數不高(gao)(gao)。
秦漢(han)(han)、隋唐黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)是(shi)中(zhong)(zhong)國的(de)政(zheng)治、經濟中(zhong)(zhong)心(xin),人(ren)日(ri)與土(tu)(tu)(tu)(tu)(tu)(tu)(tu)地(di)(di)(di)利用(yong)變(bian)化(hua)較大(da)。秦統(tong)(tong)一(yi)(yi)(yi)(yi)全國后統(tong)(tong)治范圍向(xiang)北(bei)推(tui)進到黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)北(bei)部秦長城一(yi)(yi)(yi)(yi)線(xian)。西(xi)(xi)(xi)漢(han)(han)時(shi)期(qi)統(tong)(tong)治范圍進一(yi)(yi)(yi)(yi)步向(xiang)北(bei)、向(xiang)西(xi)(xi)(xi)推(tui)進,漢(han)(han)武帝時(shi)向(xiang)北(bei)到達(da)陰山,向(xiang)西(xi)(xi)(xi)到達(da)河西(xi)(xi)(xi)走廊,黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)幾(ji)乎(hu)全部都在西(xi)(xi)(xi)漢(han)(han)的(de)統(tong)(tong)治之(zhi)下。秦漢(han)(han)時(shi)期(qi)是(shi)中(zhong)(zhong)國農(nong)(nong)業(ye)發展的(de)高(gao)(gao)峰(feng),農(nong)(nong)耕文化(hua)大(da)舉進入(ru)黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan),從(cong)綏德、米(mi)(mi)脂一(yi)(yi)(yi)(yi)帶(dai)出土(tu)(tu)(tu)(tu)(tu)(tu)(tu)的(de)漢(han)(han)畫像(xiang)石可(ke)以清楚地(di)(di)(di)反映出這一(yi)(yi)(yi)(yi)點。西(xi)(xi)(xi)漢(han)(han)時(shi)曾向(xiang)黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)大(da)量(liang)移民,再加上大(da)批(pi)吏卒屯守邊防,黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)人(ren)口迅速增加。據《漢(han)(han)書·地(di)(di)(di)理志(zhi)》記載,西(xi)(xi)(xi)漢(han)(han)元始(shi)二年(2年)黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)地(di)(di)(di)區(qu)有(you)人(ren)口880萬人(ren),其中(zhong)(zhong)洛陽(yang)盆地(di)(di)(di)人(ren)口密(mi)度高(gao)(gao)為(wei)132人(ren)/平(ping)方千(qian)米(mi)(mi),關(guan)中(zhong)(zhong)為(wei)30一(yi)(yi)(yi)(yi)90人(ren)/平(ping)方千(qian)米(mi)(mi),陜(shan)北(bei)及晉西(xi)(xi)(xi)北(bei)為(wei)10一(yi)(yi)(yi)(yi)13人(ren)/跑(pao)平(ping)方千(qian)米(mi)(mi),天(tian)水(shui)盆地(di)(di)(di)為(wei)10.74人(ren)/平(ping)方千(qian)米(mi)(mi)。人(ren)口的(de)增加和(he)農(nong)(nong)耕的(de)發展使部分林草地(di)(di)(di)被(bei)開墾(ken),但開墾(ken)程度較高(gao)(gao)主要(yao)(yao)在南部的(de)關(guan)中(zhong)(zhong)、洛陽(yang)盆地(di)(di)(di)和(he)天(tian)水(shui)盆地(di)(di)(di),當時(shi)農(nong)(nong)牧業(ye)界線(xian)在太原(yuan)一(yi)(yi)(yi)(yi)龍(long)門一(yi)(yi)(yi)(yi)寶雞一(yi)(yi)(yi)(yi)線(xian)。此線(xian)以北(bei)的(de)廣大(da)黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)丘陵地(di)(di)(di)區(qu)耕地(di)(di)(di)主要(yao)(yao)分布(bu)在河谷(gu)平(ping)原(yuan),其余地(di)(di)(di)區(qu)仍保持自然狀態。東漢(han)(han)、三(san)國、兩晉、十六國、南北(bei)朝時(shi)期(qi)黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)戰爭頻繁,社會動亂,人(ren)口大(da)量(liang)減少,原(yuan)來的(de)農(nong)(nong)耕區(qu)向(xiang)南退縮,黃(huang)(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)(tu)(tu)高(gao)(gao)原(yuan)的(de)廣大(da)地(di)(di)(di)區(qu)重新成為(wei)游牧區(qu),生態環境得(de)以恢復(fu)。
據(ju)(ju)《續漢(han)(han)書·郡(jun)國志》記載(zai),東(dong)漢(han)(han)永和五(wu)年(nian)(nian)(140年(nian)(nian))黃土(tu)高(gao)(gao)原總人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)為(wei)(wei)507.6萬人(ren)(ren)(ren)(ren)(ren)(ren),比西(xi)漢(han)(han)減(jian)(jian)(jian)(jian)(jian)少(shao)(shao)了43%。當(dang)(dang)時(shi)陜北(bei)及(ji)晉西(xi)北(bei)人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)4.94萬人(ren)(ren)(ren)(ren)(ren)(ren),比西(xi)漢(han)(han)的(de)(de)130.55萬人(ren)(ren)(ren)(ren)(ren)(ren)減(jian)(jian)(jian)(jian)(jian)少(shao)(shao)96%,人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密度減(jian)(jian)(jian)(jian)(jian)為(wei)(wei)0.5人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)以下。西(xi)晉時(shi)黃土(tu)高(gao)(gao)原人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)比東(dong)漢(han)(han)又有減(jian)(jian)(jian)(jian)(jian)少(shao)(shao),據(ju)(ju)《晉書·地理(li)志》記載(zai),西(xi)晉太(tai)康元年(nian)(nian)(280年(nian)(nian))黃土(tu)高(gao)(gao)原總人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)204萬人(ren)(ren)(ren)(ren)(ren)(ren),比東(dong)漢(han)(han)減(jian)(jian)(jian)(jian)(jian)少(shao)(shao)4%5。《晉書》中(zhong)山(shan)西(xi)河(he)曲、偏(pian)關、保德、陜北(bei)、隴東(dong)馬連河(he)流域為(wei)(wei)游牧民族居住區,無(wu)人(ren)(ren)(ren)(ren)(ren)(ren)日記載(zai),人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)當(dang)(dang)比東(dong)漢(han)(han)時(shi)更為(wei)(wei)稀疏。當(dang)(dang)時(shi)西(xi)安(an)附近(jin)的(de)(de)京(jing)兆人(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密度為(wei)(wei)34.88人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),關中(zhong)東(dong)部的(de)(de)左(zuo)馮詡(xu)為(wei)(wei)3.29人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),關中(zhong)西(xi)部的(de)(de)右扶(fu)風為(wei)(wei)9.46人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),洛(luo)陽附近(jin)為(wei)(wei)55.85人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),天水附近(jin)為(wei)(wei)5.55人(ren)(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)k/耐(nai),比西(xi)漢(han)(han)時(shi)減(jian)(jian)(jian)(jian)(jian)少(shao)(shao)l2/以上。
隋(sui)(sui)唐時(shi)中(zhong)國重(zhong)新歸于統一(yi),而且社會安(an)定(ding),經(jing)濟(ji)(ji)繁榮,成為中(zhong)國農業(ye)(ye)(ye)發(fa)展(zhan)的(de)(de)第二(er)個鼎盛(sheng)時(shi)期。隨(sui)著經(jing)濟(ji)(ji)的(de)(de)發(fa)展(zhan),黃(huang)(huang)土高(gao)原(yuan)(yuan)(yuan)人(ren)口(kou)(kou)(kou)(kou)增加,農耕(geng)業(ye)(ye)(ye)逐步代替游(you)牧(mu)業(ye)(ye)(ye)。《隋(sui)(sui)書(shu)·地(di)(di)(di)理志》記(ji)載,隋(sui)(sui)大業(ye)(ye)(ye)五(wu)年(nian)(609年(nian))黃(huang)(huang)土高(gao)原(yuan)(yuan)(yuan)總人(ren)口(kou)(kou)(kou)(kou)為1104萬(wan)人(ren),是西(xi)(xi)漢(han)的(de)(de)125%、西(xi)(xi)晉的(de)(de)5.14倍(bei)。陜(shan)北(bei)、晉西(xi)(xi)北(bei)人(ren)口(kou)(kou)(kou)(kou)密度己經(jing)趕上了西(xi)(xi)漢(han),徑河上游(you)、馬連河上游(you)己是西(xi)(xi)漢(han)的(de)(de)數(shu)倍(bei),唐初實(shi)行均田制,關(guan)中(zhong)大興水(shui)利,不(bu)僅使(shi)關(guan)中(zhong)、汾河下(xia)游(you),洛陽盆地(di)(di)(di)全部(bu)成為農業(ye)(ye)(ye)區,而且農耕(geng)業(ye)(ye)(ye)擴大到地(di)(di)(di)勢較(jiao)高(gao)的(de)(de)黃(huang)(huang)上臺源、北(bei)山南(nan)麓(lu)黃(huang)(huang)土覆(fu)蓋的(de)(de)山前平源。農耕(geng)區還沿渭河向(xiang)西(xi)(xi)到達天(tian)水(shui)、隴(long)西(xi)(xi),直(zhi)至(zhi)涅水(shui)湟水(shui)河谷地(di)(di)(di)。天(tian)寶時(shi)(742一(yi)755年(nian))唐代經(jing)濟(ji)(ji)達到了頂(ding)峰,當時(shi)黃(huang)(huang)土高(gao)原(yuan)(yuan)(yuan)人(ren)口(kou)(kou)(kou)(kou)1015萬(wan)人(ren),關(guan)中(zhong)、汾河下(xia)游(you)、洛陽盆地(di)(di)(di)人(ren)口(kou)(kou)(kou)(kou)密度50-100人(ren)/平方(fang)千米(mi)。隋(sui)(sui)唐時(shi)期基(ji)本奠定(ding)了黃(huang)(huang)上高(gao)原(yuan)(yuan)(yuan)南(nan)部(bu)農業(ye)(ye)(ye)生產的(de)(de)格局,人(ren)口(kou)(kou)(kou)(kou)增加,植被破壞(huai),城鎮興起(qi),對這一(yi)地(di)(di)(di)區土壤侵蝕產生了明(ming)顯的(de)(de)影響(xiang)。但(dan)黃(huang)(huang)土高(gao)原(yuan)(yuan)(yuan)中(zhong)部(bu)、北(bei)部(bu)自然環境的(de)(de)總體破壞(huai)程度并不(bu)甚嚴重(zhong),黃(huang)(huang)土丘陵(ling)地(di)(di)(di)區畜牧(mu)業(ye)(ye)(ye)仍占較(jiao)大比重(zhong)。
唐(tang)以(yi)后(hou)的(de)五(wu)代十國(907一979年(nian))黃(huang)土高原(yuan)(yuan)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)有(you)較大(da)(da)幅(fu)度減少(shao),但(dan)到(dao)宋代人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)得到(dao)恢復。據研(yan)究南(nan)(nan)宋嘉定三年(nian)(1210年(nian))山(shan)西人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密(mi)(mi)(mi)度為(wei)45.72人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),陜(shan)(shan)西為(wei)21.44人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)。北(bei)宋在(zai)黃(huang)上(shang)高原(yuan)(yuan)上(shang)形(xing)成(cheng)一條(tiao)(tiao)(tiao)與遼、西夏(xia)對(dui)峙的(de)軍(jun)事(shi)分(fen)(fen)界(jie)線(xian)(xian)(xian),這條(tiao)(tiao)(tiao)界(jie)線(xian)(xian)(xian)東起大(da)(da)同以(yi)南(nan)(nan),經(jing)陜(shan)(shan)北(bei)、寧夏(xia)南(nan)(nan)部、蘭州以(yi)北(bei)直至西寧以(yi)西,綿延1000千(qian)(qian)(qian)米(mi)(mi)。沿這條(tiao)(tiao)(tiao)分(fen)(fen)界(jie)線(xian)(xian)(xian),北(bei)宋修(xiu)筑(zhu)了大(da)(da)量城(cheng)鎮(zhen)、堡寨、派駐大(da)(da)批軍(jun)隊戍邊(bian)防衛(wei)。為(wei)解決軍(jun)隊給養,招募(mu)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)沿邊(bian)屯(tun)耕(geng),沿分(fen)(fen)界(jie)線(xian)(xian)(xian)形(xing)成(cheng)了一條(tiao)(tiao)(tiao)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)稠密(mi)(mi)(mi),墾殖程度較高的(de)地帶,也使此分(fen)(fen)界(jie)線(xian)(xian)(xian)所經(jing)地區生態嚴重惡化(hua)。此線(xian)(xian)(xian)以(yi)南(nan)(nan)的(de)黃(huang)土丘陵溝壑(he)區仍(reng)然以(yi)牧(mu)為(wei)主(zhu),與唐(tang)代后(hou)期(qi)比較,土地利(li)用沒有(you)太(tai)大(da)(da)變化(hua)。元代統一后(hou),黃(huang)上(shang)高原(yuan)(yuan)雖結束(shu)了軍(jun)事(shi)對(dui)壘,但(dan)元代連年(nian)殘酷的(de)戰爭和元對(dui)漢(han)人(ren)(ren)(ren)(ren)(ren)實行的(de)屠殺政策,黃(huang)土高原(yuan)(yuan)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)大(da)(da)幅(fu)減少(shao),元至元二十七年(nian)(1290年(nian))山(shan)西人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密(mi)(mi)(mi)度僅為(wei)8.20人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),陜(shan)(shan)西2.57人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),寧夏(xia)2.82人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi),甘肅2.15人(ren)(ren)(ren)(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)。
明代黃(huang)土(tu)(tu)高(gao)原人(ren)(ren)口得到恢(hui)復,明弘治四年(1491年)山(shan)西(xi)(xi)人(ren)(ren)口密(mi)度達到31.6人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),陜西(xi)(xi)15.68人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),寧(ning)夏5.02人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),,甘(gan)肅4.41人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),青海1.45人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi)。明自建國之初就在黃(huang)土(tu)(tu)高(gao)原北(bei)部修(xiu)筑(zhu)長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng),在修(xiu)建長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)的(de)同時,沿長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)大興城(cheng)(cheng)(cheng)鎮聚落,移民實邊,長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)沿線(xian)形成人(ren)(ren)口密(mi)集的(de)地帶(dai),其(qi)(qi)人(ren)(ren)口遠較長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)以(yi)南(nan)的(de)黃(huang)土(tu)(tu)丘陵溝壑區(qu)稠密(mi)。如嘉慶《重修(xiu)一統(tong)志》記載(zai),嘉慶二十五年(1820年)山(shan)西(xi)(xi)寧(ning)武人(ren)(ren)口密(mi)度為(wei)(wei)40.26人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),保德為(wei)(wei)50.64人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),而其(qi)(qi)南(nan)部的(de)爆州僅(jin)22.88人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi);榆林(lin)人(ren)(ren)口密(mi)度41.99人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),而其(qi)(qi)南(nan)部的(de)綏德僅(jin)33.17人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),延安僅(jin)19.58人(ren)(ren)/平方(fang)千(qian)(qian)(qian)米(mi)(mi)(mi)(mi),。當時的(de)長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)是(shi)農牧業(ye)的(de)分(fen)(fen)界(jie)線(xian),長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)沿線(xian)不僅(jin)分(fen)(fen)布著數百萬邊民,而且駐軍也三分(fen)(fen)戍守,七分(fen)(fen)屯田,每個屯田士(shi)卒(zu)須(xu)種地50畝,使長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)沿線(xian)被徹底開墾,長(chang)(chang)(chang)(chang)城(cheng)(cheng)(cheng)以(yi)南(nan)則農牧業(ye)兼有。
清代國家統一,社會(hui)安定,人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口增長快。明(ming)弘(hong)治四年(nian)(1491年(nian))黃(huang)土(tu)高(gao)原(yuan)總人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口達(da)到(dao)1500萬(wan)人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)。經200多年(nian)到(dao)嘉慶二(er)十(shi)五年(nian)(1820年(nian))人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口達(da)到(dao)1995萬(wan)。到(dao)道光二(er)十(shi)年(nian)(1840年(nian))人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口增至(zhi)4100萬(wan)人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren),達(da)到(dao)封(feng)建時代黃(huang)土(tu)高(gao)原(yuan)人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口的峰值(zhi)。1820年(nian)黃(huang)土(tu)高(gao)原(yuan)人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)口密度是:山西(xi)91.36人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),陜西(xi)61.16人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),甘肅34.24人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),寧夏31.37人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),青海(hai)6.95人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi)。其中關中、諫汾河(he)谷地(di),洛陽盆地(di)達(da)100-200人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),晉西(xi)北、陜北、隴(long)東達(da)40-80人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),如平(ping)(ping)涼82.62人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),慶陽57.33人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi),徑陽101.61人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)(fang)千米(mi)。明(ming)清時期長城以南(nan)的疏林(lin)灌(guan)叢已被連片開墾。另一方(fang)(fang)(fang)(fang)面由于人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)地(di)矛盾加劇,清末移入黃(huang)土(tu)高(gao)原(yuan)的移民(min)向人(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)(ren)煙少的山區遷移,如寧夏南(nan)部(bu)地(di)區、呂(lv)梁(liang)山西(xi)側(ce)、黃(huang)龍山區等,使這(zhe)些原(yuan)來的林(lin)區也逐步轉變為農耕(geng)區。可以說明(ming)清時期黃(huang)土(tu)高(gao)原(yuan)丘陵溝壑區徹底演變成了農耕(geng)區。
20世紀前(qian)半葉由于(yu)(yu)戰(zhan)亂和自(zi)然災害(hai),黃土高原(yuan)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)有所減少,1935年總人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)為(wei)2960萬(wan)人(ren)(ren)(ren)(ren)(ren),1949年為(wei)3936萬(wan)人(ren)(ren)(ren)(ren)(ren),人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)分布和清末沒有大(da)的(de)(de)(de)不同。建國(guo)后,黃土高原(yuan)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)增(zeng)長(chang)極快,70年代以前(qian)平(ping)均人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)增(zeng)長(chang)速度35.3‰。遠高于(yu)(yu)中(zhong)(zhong)(zhong)國(guo)的(de)(de)(de)21.2‰的(de)(de)(de)水(shui)平(ping);70年代以后人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)增(zeng)長(chang)速度14.6-21.0‰,仍高于(yu)(yu)中(zhong)(zhong)(zhong)國(guo)平(ping)均水(shui)平(ping),是中(zhong)(zhong)(zhong)國(guo)人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)增(zeng)長(chang)快的(de)(de)(de)地(di)(di)區(qu)之一。1960年總人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)達到4913.4萬(wan)人(ren)(ren)(ren)(ren)(ren),1980年達到7521.萬(wan)人(ren)(ren)(ren)(ren)(ren),1990年達到9031萬(wan)人(ren)(ren)(ren)(ren)(ren),人(ren)(ren)(ren)(ren)(ren)口(kou)(kou)的(de)(de)(de)增(zeng)加(jia)(jia)使耕地(di)(di)面(mian)積(ji)不斷(duan)增(zeng)加(jia)(jia),林地(di)(di)、草地(di)(di)面(mian)積(ji)減少。1949-1985年黃土高原(yuan)耕地(di)(di)增(zeng)加(jia)(jia)393.3x10000平(ping)方百米(mi),增(zeng)長(chang)率為(wei)30.6%。耕地(di)(di)增(zeng)加(jia)(jia)主要集中(zhong)(zhong)(zhong)在水(shui)土流失嚴重的(de)(de)(de)黃土丘陵地(di)(di)區(qu),凈(jing)增(zeng)耕地(di)(di)272x10000平(ping)方百米(mi),占黃土高原(yuan)凈(jing)增(zeng)耕地(di)(di)的(de)(de)(de)69%,使這些(xie)地(di)(di)區(qu)陷(xian)入“越(yue)窮越(yue)墾(ken)(ken),越(yue)墾(ken)(ken)越(yue)窮”的(de)(de)(de)經濟(ji)、生態雙重貧困。
中國實行改革開放以后,黃(huang)土高(gao)原地(di)區的(de)(de)(de)(de)國內(nei)生產(chan)總(zong)值總(zong)量呈現持續的(de)(de)(de)(de)增長態勢。西(xi)部大開發(fa)(fa)戰略的(de)(de)(de)(de)實施成為該(gai)地(di)區2000年以后國內(nei)生產(chan)總(zong)值占中國比重(zhong)迅速(su)提高(gao)的(de)(de)(de)(de)主(zhu)要誘因,而晉陜蒙地(di)區能(neng)礦(kuang)產(chan)資源的(de)(de)(de)(de)開發(fa)(fa)則是(shi)其直接動因。黃(huang)土高(gao)原地(di)區人(ren)均國內(nei)生產(chan)總(zong)值的(de)(de)(de)(de)空間(jian)(jian)分布(bu)整體上(shang)呈現出“兩(liang)高(gao)一(yi)低(di)”的(de)(de)(de)(de)帶狀(zhuang)分布(bu)格局(ju)(ju),且這種空間(jian)(jian)分布(bu)格局(ju)(ju)明顯(xian)地(di)隨著時(shi)間(jian)(jian)受(shou)到極化增長的(de)(de)(de)(de)擾動和重(zhong)塑。能(neng)礦(kuang)資源開發(fa)(fa)、農業密集(ji)程度、人(ren)口(kou)分布(bu)狀(zhuang)況和自然(ran)本底條件等是(shi)影(ying)響該(gai)地(di)區人(ren)均國內(nei)生產(chan)總(zong)值空間(jian)(jian)分布(bu)格局(ju)(ju)及其變動關鍵的(de)(de)(de)(de)因素。