Kilauea: The World’s Most Livable Volcano Figure 1: Basaltic lava flows from Kilauea Kilauea, the most active and intensely studied shield volcano in the world, is located on the island of Hawaii (Figure 1). Shield volcanoes are extremely large volcanoes composed of layers of basaltic lava in a gently sloping dome (Figure 2). Most are volcanic islands, though some are found on continents as well. Hawaii, the youngest island in the Hawaiian Island Chain, is less than a million years old and fed by a hot spot. A hot spot is an area of long lived volcanism and high heat flow from a zone of instability near the core- mantle boundary. As the Pacific plate moved over this hot spot, successive volcanoes formed. As seen in Figure 3, the age of each Hawaiian island indicates when it was situated over the relatively stationary hot spot. More than 50 eruptions have been witnessed here since record keeping began in Most of the activity on Kilauea during the past 50 years occurred along the flanks of the volcano in a region called the East Rift Zone (Figure 4). A rift eruption here in 1960 engulfed the coastal village of Kapoho, located nearly 20 mi from its source. The longest and largest rift eruption ever recorded on Kilauea began in 1983 and continues to this day! Figure 2: Anatomy of a shield volcano Figure 3: The Hawaiian Island Chain formed over a hot spot which produced basaltic magma from partial melting of oceanic crust

Because of its lower silica content, basaltic lava is usually very fluid and flows in thin, broad sheets or stream-like ribbons. While lavas have been clocked at 19 mph, flow rates of feet per hour are more common. Two typical types of Hawaiian flows are aa and pahoehoe flows. Aa flows have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections (Figure 5a). In contrast, pahoehoe flows exhibit smooth surfaces that often resemble the twisted braids of ropes (Figure 5b). Pahoehoe means “on which one can walk.” Hardened basaltic flows commonly contain tunnels that once were nearly horizontal tubes carrying lava from the volcanic vent to the flow’s leading edge. These openings develop when the interior or a flow remains hot long after the surface hardens. In these circumstances, still-molten lava within the tubes continues its forward motion leaving behind cave-like voids. Lava tubes allow fluid lavas to advance great distances from their source (Figure 6). Figure 4: Most recent eruptions from Kilauea occur in the East Rift Zone A B Figure 5A: Aa lava flows are characterized by jagged blocks and sharp edges, while Figure 5b illustrates the ropey, fluid-like nature of basaltic pahoehoe flows.

Figure 6: View of an active lava tube as seen through the collapsed roof Kilauea Shield Volcano Questions 1.Define the following terms: a. Shield volcano: __________________ _________________________________ b. hot spot: _______________________ _________________________________ c.basaltic lava: ___________________ __________________________________ d. Pahoehoe lava: __________________ _________________________________ e. aa lava: ________________________ _________________________________ f. lava tube: ____________________________________________________________________ ______________________________________________________________________________ 2. Why does lava from Kilauea have a low viscosity? 3. Using Bowens Reaction series, what minerals compose basaltic lava? 4. What igneous texture do you expect most of the rocks on Kilauea to have? 5. Compare a composite cone and a shield volcano. Name: _______________