. The Earth beneath the sea : History . NAUTICAL MILES { \â*v- - 1800 2400 1800 mi uiii^jiav 2400' MfiROUF'^aS IS^AMDS â aiSBMMM 1800 2400 1800 r s*^ Sc err APRON WEST OF MARQUESAS 1 -,1 AN-j' ___^., -«. *' *^ .^ <v Fig. 30. Echograms of a typical archipelagic apron. The figiu-e shows a well-developed archipelagic plain. Note the contrast of the archipelagic-plain topography with the blocky topography of the mid-oceanic ridge in the central east Pacific. Note abyssal hills in Profile B. "(After Menard, 1956.) 1000 to 1500 m. Clearly, they are former active volcanoes which were i
. The Earth beneath the sea : History . NAUTICAL MILES { \â*v- - 1800 2400 1800 mi uiii^jiav 2400' MfiROUF'^aS IS^AMDS â aiSBMMM 1800 2400 1800 r s*^ Sc err APRON WEST OF MARQUESAS 1 -,1 AN-j' ___^., -«. *' *^ .^ <v Fig. 30. Echograms of a typical archipelagic apron. The figiu-e shows a well-developed archipelagic plain. Note the contrast of the archipelagic-plain topography with the blocky topography of the mid-oceanic ridge in the central east Pacific. Note abyssal hills in Profile B. "(After Menard, 1956.) 1000 to 1500 m. Clearly, they are former active volcanoes which were islands but which became inactive and subsided long before the period of vulcanism in wliich the existing islands were formed. The enormous load of a group of volcanic islands might be expected to depress the crust of the earth, and a moat or encircling depression around the southern Hawaiian Islands has been attributed to this cause (Dietz and Menard, 1953). The moat is only slightly deeper than average for the region but it, in turn, is encircled by a broad arch, which makes the moat more conspicuous (Fig. 24). Most archipelagos are not encircled by moats that are evident in the topogra])hy of the sea floor. However, abnormal thicknesses of several kilo- meters of volcanic rock lie under the sea floor in the vicinity of many archi- pelagos. Inasmuch as the sea floor is not elevated, the upper surface of the
Size: 2302px × 2170px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
