Site D: A continental magmatic arc, where volcanoes are on top of a mountain belt nearthe edge ofthe continent. The volcanoes erupt light- colored and gray volcanic rocks. Older intrusive rocks, some with coarse crystals, are also exposed. [Samples 5,6, and 7] Site A: A line of volcanic islands and submarine mountains. Broadvolcanoes on the islands are foming dark volcanic rocks. [Sample 1]. Site E: An island arc, Site B: Circular volcanic depressions (calderas) on land, which are filled with light-colored volcanic ash and light-colored volcanic rocks. which is a chain of volcanic islands adjacent to an ocearic trench. The volcanoes erupt gray volcanic ash andlava flows. There are also some [Samples 2 and 3] intrusive rocks. [Samples 8 and 9] Site C: A mid-oceanridge that zigzags across the ocean floor. The rock sample is dark colored andis from a lumpy lava flow on the seafloor. [Sample 4] Rock 3. This brown-colored rock Rock 1. This rock is dark colored, has no visible crystals, and is not glassy. It does have many vesicles (holes) and is a vol- canic rock. A chemi- Rock 2. This light-colored rock is finely crys- talline and not glassy. It contains some fine- grained gray crystals and a few small holes. A chemical analysis documents that it is a felsic rock. It was collected on a volcano. contains large, light-colored lenses of flattened pumice in a finely crystalline matrix. Under the microscope, the matrix contains compacted volcanic ash, along with small crystals and fragments of other rocks. The crystals are mostly quartz and K-feldspar. cal analysis revealed a relatively low silica content. Rock 4. This rock is finely crystalline and lacks visible crystals. It has a dark-gray color. A chemical analysis of the sample indicates that it is a mafic rock. Rock 6. This rock 2 has very large crys- tals, some of which are 5 to 10 cm long. Most of the rock is K-feldspar and quartz, and the dark crystals are a type of amphibole that is most common in felsic rocks. 4 Rock 5. This porous rock in the center of the photograph has numerous holes and is extremely lightweight. It is light colored and is composed of vol- canic glass. There are no visible crys- tals, but the rock is likely to be felsic in composition. Rock 9. This rock contains large crys- tals of K-feldspar in a brown-colored matrix of small to medium-sized 7. 8. crystals. There is no glass, ash, or Rock 7. This medium-grained rock is a plutonic rock. It has a Rock 8. This rock has scattered visible crystals of salt-and-pepper appearance, caused by the presence of felsic amphibole and biotite in a medium-gray, finely crystal- vesicles, so the rock minerals (feldspar and quartz) and mafic minerals (mostly bio- tite mica). It is intermediate in composition. line matrix. It reportedly was collected either on a vol- is probably not a cano or from dikes exposed near a volcano. volcanic rock.

For Site B, use the rock samples to predict whether the magma for that site has a high or low viscosity and whether the volcano would erupt explosively or effusively.