In the past half-million years, Mauna Kea has supported an ice cap at least four times. These glaciations occur when the climate is cold and wet, when more snow falls each year than melts. In the past half-million years, Mauna
In the past half-million years, Mauna Kea has supported an ice cap at least four times. These glaciations occur when the climate is cold and wet, when more snow falls each year than melts.
Ice caps are large glaciers in which ice flows outward in all directions from the cap’s thickest points. As the ice flows, it erodes the surface, picking up and transporting underlying rocks and ash, and eventually deposits them as garlands of loose debris at the edge of the ice cap. Geologists interpret these deposits, known as end moraines, to infer the extent of past ice-cover and to provide clues about the climatic history of Hawaii’s alpine environments.
Since it is always cold at the summit of Mauna Kea, why is there no ice cap today? East Hawaii has no shortage of moisture, and Mauna Kea receives much more snow each winter than do many of the ice caps in the polar regions. The warm summer temperatures on modern Mauna Kea prohibit glaciation, however, since nearly all of the snow and ice melt away.
What might depress summer temperatures enough to grow an ice cap? Elevation is one factor. The atmosphere gets roughly 3.5 degrees Fahrenheit colder for every 1,000 feet of elevation gain. At over 14,000 feet above sea level, it is reasonable to expect the summit of Mauna Kea to be about 50 degrees colder than Hilo.
Rapid growth of the island through volcanic processes has increased its mass enough that the island has sunk under its own weight. During the most recent Mauna Kea glaciation, 14,000 years ago, the summit was only about 150 feet higher than it is today. Elevation alone is not enough to explain why ice caps persisted on Mauna Kea, because we see evidence that they reached as low as 11,000 feet.
Glaciations are also controlled by the amount of solar radiation, heat, that reaches Earth’s surface. Changes in the shape of Earth’s orbit around the sun and in the orientation of Earth’s rotational axis affect the amount and distribution of the radiation. The color and roughness of Earth’s surface determine whether the radiation is reflected or absorbed and re-emitted as heat. The composition of the atmosphere controls whether the reflected radiation is directed away from Earth or back toward it.
Wearing light colors helps a person stay cooler. A large polar ice cap does the same for the planet. A large ice cap at the North or South Pole changes the color of part of the planet from green, blue or brown, to white. The snow reflects most of the radiation that hits Earth. Cooling at the poles is enough to impact the surrounding area significantly and likely depresses temperatures globally.
Low levels of greenhouse gases — mainly water vapor, carbon dioxide and methane — decrease the amount of radiation that is absorbed and re-emitted back toward Earth, ultimately causing temperatures to decrease. Analyses of gases trapped in ice cores reveal that three of the four glaciations on Mauna Kea indeed correspond to low levels of greenhouse gases in the atmosphere.
The Mauna Kea glaciations also correspond to glaciations elsewhere in the world, indicating that the planet was cooler than it is today. Furthermore, computer models estimating solar radiation using Earth’s orbital configuration show that three Mauna Kea glaciations occurred at times of predicted low radiation.
Today, measurements taken on Mauna Loa show increasing atmospheric concentrations of greenhouse gases. Solar radiation may be decreasing, though not quickly enough to offset the warming effects of the elevated levels of greenhouse gases.
By looking at past geologic events, such as glaciations, we can appreciate the complex interactions between geologic cycles on this planet and the enormous influence of the sun. Can we expect another ice cap anytime soon? Elevated greenhouse gases plus the ongoing subsidence of the island make conditions unfavorable for another glaciation for at least the next couple of thousand years.
Kilauea activity update
A lava lake within the Halemaumau Overlook vent during the past week resulted in a nighttime glow visible from the Jaggar Museum overlook. The lake has been about 200 to 260 feet below the floor of Halemaumau Crater and visible by HVO’s webcam through much of the last month. This past week, the level fluctuated due to deflation-inflation cycles at the summit, reaching a high level of about 180 feet below the Halemaumau Crater floor.
On Kilauea’s east rift zone, surface lava flows on the pali and coastal plain continued advancing towards the ocean. As of Wednesday, the active flows were 1.1 miles from the ocean; there was no active ocean entry. Within the Puu Oo crater, a lava pond was active and several small lava flows were erupted onto the crater floor over the past week.
Five earthquakes were reported felt across the island of Hawaii during the last week. At 11:15 a.m. May 31, a magnitude 3.5 earthquake occurred 11 miles north of Pahala at seven miles depth. At 12:55 a.m. Monday, a magnitude 3.5 earthquake occurred nine miles southeast of Naalehu at a depth of 23 miles. At 3:23 p.m. the same day, a magnitude 3.5 earthquake occurred five miles south of Kilauea Summit at a depth of 0.5 miles. At 10:05 a.m. Tuesday, a magnitude 3.2 earthquake occurred at Kukuihaele at a depth of 22 miles. At 8:53 a.m. Wednesday, a magnitude 2.6 earthquake occurred three miles northwest of Volcano Village at a depth of five miles.
Visit hvo.wr.usgs.gov for detailed Kilauea and Mauna Loa activity updates, recent volcano photos and recent earthquakes; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.
Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.
