| 1. | graben. |
| 2. | a subsea chasm extending along the crest of a mid-ocean ridge, locus of the magma upwellings that accompany seafloor spreading. |
[grah-buhn] 
| a portion of the earth's crust, bounded on at least two sides by faults, that has dropped downward in relation to adjacent portions. |
| Great Rift Valley also Rift Valley A geologic depression of southwest Asia and eastern Africa extending from the Jordan River valley to Mozambique. The region is marked by a series of faults caused by volcanic action. |
| rift valley n. A valley that has developed along a rift, especially one bounded by normal faults in an area of lithospheric thinning. |
| Rift Valley (rĭft) See Great Rift Valley. |