What weather phenomenon can cover runway markings and cause aircraft to lose traction during takeoff and landing?

The correct answer highlights volcanic ash as a weather phenomenon that can have a significant impact on runway conditions. Volcanic ash is not just a visibility issue; when it falls on runways, it can create a very slippery surface that severely impairs an aircraft's ability to gain traction during takeoff and landing. The ash is composed of fine particles that can accumulate on the runway, making it hazardous for aircraft operations.

While fog and rain can affect visibility and may contribute to operational challenges, they do not inherently create a slippery runway surface. Rain can lead to temporary conditions like hydroplaning when water accumulates on the surface, but it does not create a physical barrier like volcanic ash. Snow also presents challenges for traction and surface conditions, including the potential for icy surfaces, but the specific characteristics of volcanic ash—such as its abrasiveness and how it interacts with aircraft tires—distinguish it as a particularly dangerous phenomenon for runway markings and traction.

Overall, the unique effects of volcanic ash in aviation contexts underscore its risks during critical flight phases, making it the appropriate answer to this question.