Shield volcano are cave-like volcanic straights formed by the hardening of overlaying lava. These structures help further the propagation of lava, as the walls of the tube insulates the lava within. Lava tubes can account for a large portion of shield volcano activity; for example, an estimated 58% of the lava forming Kīlauea comes from lava tubes. In some shield volcano eruptions, basaltic lava pours out of a long fissure instead of a central vent, and shrouds the countryside with a long band of volcanic material in the form of a broad plateau. Plateaus of this type exist in Iceland, Washington, Oregon,
Mud volcano abyssal plains. Most liquid and solid material is released during eruptions, but seeps occur during dormant periods. The mud is rich in halite (rock salt). First-order estimates of mud volcano emissions have been made (1 Tg = 1 million metric tonnes). Dozens of mud volcanoes can be found on the Taman Peninsula of Russia and the Kerch Peninsula of Crimea along with the south-western portion of Bulgaria near Rupite. In Italy, they are common in the northern front of the Apennines and in Sicily. On August 24, 2013, a mud volcano appeared in the centre of the via Coccia di