Sandstorms are strong dry winds blowing over the desert that raise and carry along clouds of sand or dust often so dense as to obscure the sun and reduce visibility almost to zero; also known as a duststorm. Such a wind is usually the result of convection currents created by intense heating of the ground. The wind is strong enough to move dunes, and it often interferes with travel, sometimes obliterating roads in flat dry regions such as those of the W United States. The simoom (or simoon) is the dust- and sand-laden desert wind of N Africa and Arabia that contributes largely to the atmospheric dust over Europe; evidence of the dust from simoon winds has also been found on the seafloor at considerable distances from shore. The haboob is a sandstorm prevalent in the region of Sudan around Khartoum. Sandstorms, the leading edges of which often appear as solid walls of dust.