Lava broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A caldera, which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means
Lava Cast Forest 1942, the United States Forest Service designated 5,120 acres as part of the Lava Cast Forest Geological Area and were promoted as a tourist attraction. In 1963, scientists from NASA became interested in the lava fields because they had very little erosion and they suspected it might be what they would find on the surface of the Moon. From 1964 to 1966, at least 46 astronauts trained for lunar missions in the area. James B. Irwin delivered a rock from one of Oregon's lava flows to the lunar surface to commemorate NASA's experiences in central Oregon. Lava Cast Forest Lava