‘Knobby terrain’ a sign of Mars’ explosive past

figure-4The 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…. 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. [A paper published in Geophysical Research Letters by Jun Huang and Long Xiao (China University of Geosciences, Wuhan) now contributes much more evidence.]

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… [More at link]

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