Welcome to the "Planetary Geology on Earth: Shield Volcanoes" Earthcache! If you are at the earthcache coordinates you are on the slopes of the shield volcano Mauna Kea. In this geological adventure, we will explore the intriguing similarities and differences between shield volcanoes on Earth, particularly in Hawaii, and those on the enigmatic Martian landscape. As we delve into the fascinating world of volcanic geology, we'll discover how these two worlds share common volcanic features while revealing their unique characteristics.
Similarities:
Basaltic Composition: Both Mars and Hawaii have shield volcanoes primarily composed of basaltic lava, which is relatively low in viscosity. This low viscosity allows lava to flow easily, creating the characteristic broad, gently sloping shield shape.
Eruption Style: Both types of shield volcanoes are characterized by non-explosive eruptions. Lava flows out of fissures or vents on the volcano's surface, creating extensive lava fields.
Gentle Slopes: Shield volcanoes on both Mars and in Hawaii have relatively shallow slopes. This shape is a result of the flowing lava, which spreads out horizontally rather than piling up steeply.
Differences:
Size: Mars hosts some of the largest shield volcanoes in the solar system. For example, Olympus Mons, the largest volcano on Mars and the largest mountain in the Solar System, stands about 72,000 feet high and has a diameter of about 370 miles. In contrast, Hawaiian shield volcanoes like Mauna Kea are much smaller, with Mauna Kea being the tallest mountain on Earth with a height of around 32,696 feet measured from its base on the ocean floor to its summit 13,796 feet above sea level.
Atmosphere: Mars has a very thin atmosphere composed mainly of carbon dioxide. This affects the way eruptions occur, as the lack of significant atmospheric pressure makes lava flows more fluid and potentially longer than their counterparts on Earth. In Hawaii, eruptions occur in a denser atmosphere with a different composition, impacting the behavior of volcanic gases and lava flows.
Tectonic Setting: Hawaiian shield volcanoes are formed due to the movement of the Pacific Plate over a hotspot, where a plume of hot mantle material rises to the surface. After a couple of million years of plate movement, the volcano is moved away from the hotspot and the volcano goes extinct. In contrast, Martian shield volcanoes like Olympus Mons are thought to have formed primarily from volcanic activity at a stationary hotspot, without the influence of tectonic plate movement. Unlike on Earth, the crust of Mars remains fixed over a stationary hotspot, and a volcano can continue to discharge lava until it reaches an enormous height.
Age and Activity: Hawaiian shield volcanoes are still active and continue to erupt periodically. In contrast, the shield volcanoes on Mars are considered extinct, with their last eruptions occurring millions of years ago. This difference in activity is related to the unique geological history and conditions on each planet.
Task 1:
Observe the gently sloping terrain at this location. How do you think it would it compare to the appearance of a shield volcano on Mars?
Task 2:
Imagine the volcanic activity that may have occurred here at Mauna Kea in the past. How do you think it compares to the volcanic history of Mars' shield volcanoes like Olympus Mons?
Task 3:
Standing at the earthcache coordinates on a typical clear day you can see the summits of five shield volcanoes. Kohala to the Northeast. Mauna Kea to the southeast. Mauna Loa to the south. Hualalai to the southwest. Haleakala to the north. On an extremely clear day you can see West Maui Mountain and Kaho’olawe to the west of Haleakala. How many could you see on your visit?
Task 4:
Observe the lava rocks around you. There are two main types of lava flows in Hawaii. "Ropey" and smooth pahoehoe lava and a’a lava that does not flow as far, is sharp, and form clinkers when flowing. Which of the two types is present at the Earthcache coordinates?
Task 5:
Post a picture showing the viewing conditions on the day you visited the Earthcache.
Mahalo!