Aulacogens can become a filled graben, or
sedimentary basin surrounded by a series of
normal faults. These can later become the pathway for large river systems such as the
Mississippi River. The rock forming an aulacogen is brittle and weak from when the rift zone was active, causing occasional volcanic or
seismic activity. Because this is an area of weakness in the crust, aulacogens can become reactivated into a rift zone. An example of a reactivated aulacogen is the
East African Rift or the
Ottawa-Bonnechere Graben in
Ontario and
Quebec,
Canada, an ancient aulacogen that reactivated during the breakup of
Pangaea. Abandoned rift basins that have been uplifted and exposed onshore, like the
Lusitanian Basin, are important analogues of deep-sea basins located on conjugated margins of ancient rift axes. ==Examples==