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This week from AGU: Iceberg sounds, underground water reserves, volcanoes on Mars

American Geophysical Union

From AGU's blogs: Distinctive sounds announce iceberg births (+ video)

Underwater sounds can be used to detect different ways glaciers lose ice as they flow into the ocean, giving scientists new insight into these poorly understood events, according to new research.

Scientists used underwater microphones aboard buoys to record a variety of iceberg births at the Hans Glacier in Svalbard, Norway during three days in August 2013. These recordings were combined with time-lapse photos of the glacier during the same time period.

By synchronizing the sound recordings with the photographs, the researchers discovered that different types of ice loss are associated with distinct rumbles, snaps and splashes, according to a new study accepted for publication in Geophysical Research Letters. See a video of the events here.

From Eos.org: Underground Water Reserves Found in Hawaii's High Country

The newly discovered groundwater resource could be a source of geothermal energy in a place where electricity rates are the highest in the United States.

From AGU's journals: "Knobby terrain" a sign of Mars's explosive past

The Red Planet's upper crust is brittle and weak. Planetary geologists often attribute this to effusive eruption--lava pouring out of a volcano onto the ground--early in Mars's history with later modifications. However, some have suggested that the friable materials were created by widespread ash-laden explosive volcanoes that were eroded by geologic processes over the course of Martian history.

Scientists have a tough time sorting out these different origin theories because ancient volcanoes were ultimately buried by lava from more recent eruptions. However, several volcanic regions have been identified in recent years that are home to some of the Red Planet's oldest volcanoes. These ancient regions, Circum-Hellas and Arabia Terra, also hint at a history of explosive eruptions.

Huang and Xiao identified 75 additional ancient volcanoes across Mars's surface. Using high-resolution satellite images and heat-sensing instruments, the researchers found a unique knobby terrain in 17 of those volcanoes. The pair also noticed similarities to eroded features on Earth called ignimbrites, which form as a result of huge explosions of pyroclastic ash and rock flowing down volcanic slopes. The comparison is supported by spacecraft data showing that the features are made of a fine-grain material. Spectral data also indicate that the knobby features were eroded by liquid at some point in the past.

The scientists interpret their observations as a sign that these knobby features formed in pyroclastic explosions early on Mars and were later eroded. If the finding is correct, it would lend support to the theory that explosive volcanism was common on Mars in the distant past.

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