Final answer:
When horizontal pressure, often due to tectonic forces, is applied to rocks, it causes deformation that typically results in lines or geological structures perpendicular to the pressure. This is observed in the formation of fold mountains such as the Alps.
Step-by-step explanation:
When horizontal pressure is applied to rocks, it affects the Earth's surface by causing deformation of the crust. If the pressure is compressional, it can lead to the formation of fold mountains, where the Earth's surface is pushed upwards, resulting in lines that are typically perpendicular to the direction of the pressure.
This is because the rock layers are squeezed together, and folds are created with their axes oriented perpendicular to the maximum stress direction. Such deformation is evident in mountain ranges like the Alps, where plate tectonic activities have pushed the Earth's crust into towering peaks.
The answer to the question is that when horizontal pressure is applied to rocks, option 1) will occur: it will form lines that are perpendicular to the direction of the pressure. The strike and dip of rock formations can be used by geologists to understand the direction of the past pressures that have shaped them.