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Volcano Watch — Frozen in time: ice and snow yield secrets from the past

December 8, 2005

Hawai`i Island residents and visitors eagerly awaiting the season's first snowfall were rewarded this past week. By Wednesday morning, a light dusting of snow was visible on the upper slopes of Mauna Kea and Mauna Loa.

Snow-capped Mauna Loa volcano.
Snow-capped Mauna Loa volcano.

The seasonal ritual of transporting snow from the summit of Mauna Kea will likely begin soon, and occasionally an ephemeral snowman will appear in front of a Hilo home. Once or twice each winter, depending on conditions, ski and snowboard competitions are hastily organized on Mauna Kea and provide short-lived recreational opportunities for snow sport enthusiasts.

In colder environments with persistent snow, the novelty of a Hawaiʻian winter wonderland may be lacking, but the enduring snow and ice can yield secrets from the past. For instance, long records of global climate are buried in glaciers and in the polar ice sheets of Greenland and Antarctica.

In areas where temperatures are generally below freezing, each year's snow is added on top of the previous years' unmelted layers. Material in the atmosphere, including dust, ash, gases, and particles are washed out of the air and remain behind in that year's snow layer. As more snow piles up, it is compacted into layers of ice, a layer for each year, with the deposited atmospheric material preserved in each layer.

Samples are collected from the ice sheets by driving a hollow tube deep into the sheet and removing a long cylinder of ice. These ice cores, which can be as much as 3.2 km (2 miles) long, provide a systematic record of the composition and temperature of the Earth's atmosphere over the past million years.

Tiny bubbles of ancient air trapped within the ice provide a direct look at the atmosphere's abundance of greenhouse gases through the ages. Ice core studies provide evidence of the dramatic impact that human activity has had on the planet since the industrial revolution, when greenhouse gases and pollutants, such as sulfates and nitrates, increased significantly.

Some of the events that can be discerned in the ice core record include the leveling off of sulfate and nitrate levels after the 1972 clean air act went into effect; a radioactive signature from the Chernobyl nuclear accident in 1986; the beginning of atomic-bomb testing in the mid-1950s; an increase in sea storminess that occurred toward the end of the 14th century (as indicated by the sea salt signature); and periods of rapid climate change. One example shows that around 12,000 years ago average temperatures plunged approximately 27 degrees F., possibly in less than a five year period.

Volcanic eruptions also leave a distinct marker within ice cores. Ash, sulfate particles, gases, and acidity can all be measured. The resulting time series is the most reliable means of developing continuous records of past volcanic activity and assessing the impact of global volcanism on climate and the environment.

Ice core studies have revealed that volcanic eruptions have shaped human history in unsuspected ways. For example, one researcher identified that the timing of the seven largest volcanic eruptions of the last 2,000 years were followed by known outbreaks of plague (except for one eruption, which occurred while a plague pandemic was already underway). Plague pandemics and major volcanic eruptions are both so rare that the odds of them occurring together by chance are very small.

However, major volcanic eruptions can drastically alter global climate by producing a vast aerosol haze that blocks sunlight and lowers temperatures worldwide. This causes an increase in clouds and rainfall, which can result in crop failures and famines. A starving, weakened population is more susceptible to illness, and hungry rats are driven from the failed fields into human food supplies. The rats bring diseases, such as the plague bacteria, which thrive in the cool, moist conditions created by major volcanic eruptions.

A volcanologist's fantasy might include the presence of ice cores on Mauna Kea. The information they could provide about significant eruptions in the early history of Hawaiʻian volcanoes might help reveal how the human and natural environment have been shaped by volcanism here in Hawai`i.

Volcano Activity Update

Eruptive activity at Pu`u `O`o 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 Pu`u `O`o to the ocean, with a few surface flows breaking out of the tube. In the past week, flows were active on the steep slopes of Pulama pali, above the coastal plain. Surface flows on the pali are visible at night (weather permitting) from the end of Chain of Craters Road.

As of December 8, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. A new bench continues to grow in the embayment created during the large bench collapse on November 28. The truncated lava tube, initially hosting a fire hose-like stream of lava freefalling into the water, has crusted over to form a steep ramp leading down to the bench. Most of the lava is passively entering the ocean with little fanfare. A few littoral explosions from the front of the rapidly growing bench, however, have been large enough to bombard the top of the sea cliff behind the ocean entry with spatter.

During the week ending December 7, there were no felt earthquakes reported on Hawai`i Island. A magnitude-4.7 earthquake occurred at 1:42 a.m. on Wednesday, December 7 and was located 8 km (5 miles) east of Lo`ihi seamount. This earthquake occurred a few hours after a flurry of earthquakes began in the Lo`ihi region early in the evening on December 6.

Mauna Loa is not erupting. During the past week, six earthquakes were located beneath the volcano. Inflation continues but has slowed over the past several weeks.