Science Olympiad Dynamic Planet Practice Test

Which statement describes a horst?

1. A valley that experiences an upward displacement

2. A raised block of the Earth's crust bounded by normal faults

3. A region exhibiting mass wasting events

4. A process involving the sinking of the crust

The correct answer is: A raised block of the Earth's crust bounded by normal faults

A horst is characterized as a raised block of the Earth's crust that is bordered by normal faults. This geological feature typically forms in tectonically active regions where the Earth's crust is subjected to extensional forces. As these forces pull the crust apart, blocks of the crust can either sink or be uplifted. Specifically, within this context, the horst rises relative to the surrounding blocks, which may be undergoing downward movement, often referred to as grabens. This contrasts with the other options, which describe different geological processes or features that do not pertain to the defining characteristics of a horst. For instance, a valley experiencing an upward displacement does not accurately represent the typical formation or features of a horst, which is fundamentally about the elevation of crustal blocks rather than valleys. Similarly, mass wasting refers to the movement of soil and rock down a slope, which does not inherently involve the definitions of a horst. Lastly, the description of a process involving the sinking of the crust pertains more to tectonic subsidence, which again diverges from the uplift characteristics that define a horst. Thus, the identification of a horst as a raised block between normal faults is crucial for understanding its formation and geological significance.