What are divergences and typical hazards associated with divergent boundaries on land and at mid-ocean ridges?

• A. Divergent boundaries are transform boundaries with large earthquakes.
• B. Divergent boundaries have extensional tectonics; earthquakes generally smaller, but volcanism occurs; on land, rifting can create grabens and lakes; hazard includes volcanic activity.
• C. Divergent boundaries always produce big subduction earthquakes.
• D. Divergent boundaries have no hazards.

Answer: (B)

Divergent boundaries involve plates moving apart, causing extension. As they pull away, mantle magma rises to fill the gap and new crust forms, so volcanism is common and earthquakes tend to be smaller and shallower than at subduction zones. On land, this extensional squeezing creates rift valleys with grabens, and these rifts can fill to form lakes. The hazards reflect this activity: volcanic eruptions along the rift, ground deformation and cracking, and potential flooding or instability associated with the developing lakes. At mid-ocean ridges, the same upwelling creates new oceanic crust; earthquakes are frequent but usually small, and volcanism along the ridge axis is typical, with hydrothermal activity common. This matches the description of extensional tectonics, generally smaller earthquakes, and volcanism, with land rifts forming grabens and lakes, and volcanic hazards.