At the base of Olympus Mons... (ctx frame - Natural Colors; credits: Lunar Explorer Italia)

This image is located at the foot of the largest volcano of the Solar System: Olympus Mons.

The entire scene is covered with a multitude of Lava Flows. Most of the Flows consisted of relatively sticky lava that froze after flowing for only a short distance (often less than 1 Km, or about 1/2 a mile). However, a few of the Flows were more fluid and actually drained out of their Channels, leaving Troughs with distinct levees. These “Channelized” Flows extend out of the HiRISE image so they must be at least several kilometers (a few miles) long.

In all likelihood, both the short and long Lava Flows have very similar chemical compositions.
Based on experience with Lava Flows on Earth, the Channelized Flows were probably fed by more vigorous eruptions. That is, the Lava Flow was fed so quickly that the lava traveled a long distance before it solidified. With the shorter flows, a slow dribble of lava froze before going more than the equivalent of a few city blocks.