On the Trail of Hotspots: the Galapagos and Hawaiian Islands

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The Galapagos Islands are perhaps best known for their unique species of plants and animals and their role in influencing Charles Darwin and others in developing modern theories of evolution.

Volcan Wolf, from the island of Isabela in the Galapagos.

(Public domain.)

The relationship between the geology and biology of these islands is central to the evolution of species. For example, evidence suggests that multiple sets of Galapagos Islands were created, were carried away from the hotspot, and sank. Unusual life forms colonized each subsequent set of islands as an evolutionary stepping stone to their present place and form in the modern Galapagos.

It is interesting to note that there is a higher number of species unique to Hawaii, as compared to the Galapagos. This likely stems from the combined effects of the more isolated geographical position, the more varied topography and ecological conditions, and the greater geological age of the Hawaiian chain.

The Galapagos Islands, named after their renowned giant tortoise residents (galapago is a Spanish word for tortoise), span the equator 600 miles (1000 km) from mainland Ecuador. This archipelago, consisting of 126 islands, islets, and rocks, is comparable in number to the 132 islands, reefs, and shoals of the Hawaiian archipelago. The total dry land area of the Galapagos, however, is not quite half that of the Hawaiian Island chain.

For each archipelago, the largest island makes up around 60 percent of the dry land area and hosts the tallest volcano. Volcan Wolf, which rises 5,600 feet (1,707 m) from the island of Isabela in the Galapagos, however, is dwarfed by Mauna Kea, which soars 13,796 feet (4,205 m) above sea level on the Island of Hawaii. Both islands host five volcanoes but Isabella Island is about half the size Hawaii Island. Active volcanism for both archipelagos is ongoing; at least 60 eruptions in the Galapagos and over 90 eruptions in Hawaii have occurred over the past 200 years.

Both Hawaii and the Galapagos arise from plate movement over a hot spot. In the case of the Galapagos, the Nazca Plate is moving eastward toward the South American continent at about 37 mm (1.5 inch) per year. Unlike the Hawaiian example, the Galapagos hot spot has not produced a simple linear island chain. As would be expected from the plate motion, the most active volcanoes are on the western islands. Although the easternmost islands are farther "downstream" from the hot spot, some of them are also surfaced with young lavas. Both young and old volcanoes are strung out to the north and south, at an angle to the plate motion. The overall effect is one of several lines or a cluster of islands, rather than a single, orderly string.

As in Hawaii, older seamounts stretch away from the hot spot (in this case, two chains) - one extending to the east and the other to the northeast of the islands.

The less distinct pattern of island placement has been attributed to the more complex structural setting of the Galapagos. Unlike Hawaii, which lies in the middle of one of the earth's tectonic plates, the Galapagos are just south of an area where the edges of two plates are moving away from each other.

Known as the Galapagos Spreading Center, this mid-ocean ridge is where volcanic rock is added to the sea floor to fill the growing void between the separating plates. Often, these ridges are offset by fracture zones, or faults; the Galapagos sports a major fault just to the north of the archipelago. The fault likely added stresses and strain that affected the development of the archipelago. Evidence also suggests that the Galapagos Spreading Center has migrated over time and that it probably overlay the hotspot millions of years ago.

It is important to remember that the dynamic processes that form island chains also contribute to the unique flora and fauna that makes these environments so special.

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Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have returned to values lower than those during the period of increased activity between January 10 and March 11 of this year. The number of earthquakes located in the summit area is low (usually less than 10 per day). Inflation of the summit caldera continues, but at a noticeably slower rate than over the past two weeks.

Eruptive activity at Puu Oo continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source on the flank of Puu Oo to the ocean, with occasional surface flows breaking out of the tube. In the past week, surface flows were active on the coastal plain below Paliuli, 0.4 km (0.3 mi) inland of the coast at Kamoamoa, about 5.5 km (3.4 mi) from the end of Chain of Craters Road.

As of March 30, lava is entering the ocean at East Laeapuki, in Hawaii Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 1,100 m (3,600 ft) long by 250 m (820 ft) wide. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There was one earthquake beneath Hawaii Island reported felt within the past week. A magnitude-2.4 earthquake occurred on Wednesday, March 22, at 6:37 p.m. and was located 5 km (3 miles) south of Kīlauea summit at a depth of 3 km (2 miles).

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (one earthquake was located). Inflation continues, but at a rate that has slowed since early October 2005.