Lava Formation at Howells Point - Amazing Geology
Overview
Howells Point in New Zealand is a fascinating place to explore the region's impressive geology. Particularly striking are the well-preserved lava formations, which provide a unique insight into the Earth's volcanic past. This EarthCache offers the opportunity to better understand the formation of this particular lava form and to explore different types of lava.
LOG CONDITIONS
To log this Earthcache, go to the coordinates given in the listing and answer the questions below. Please send your answers directly by email or via the message center.
- Describe the striking characteristics of the lava formations you see at Howells Point. Pay particular attention to shape, color, and texture.
- Using the described characteristics, identify which type of lava is visible here and explain your decision.
- What geological conditions led to the formation of this lava and why can we see it today?
- Mandatory: Take a photo of yourself or a personal item at the given coordinates, without spoiling any information or answering the questions asked.
Introduction: Magma, Lava, and Pyroclasts
Magma is molten rock found beneath the Earth's crust. Magma has temperatures exceeding 1000°C and can also solidify within the Earth's crust. Magma consists of Si, Al, Fe, Mg, Ca, Na, and K oxides, as well as magmatic gases and water.
Once it reaches the Earth's surface and moves there in liquid form, it is called lava. Lava consists primarily of silicate melts with a SiO2 content of 45–70%. The temperature of lava ranges between 800°C (rhyolitic lava) and 1200°C (basaltic lava).
Pyroclasts are solid fragments of magma that are ejected into the air during explosive volcanic eruptions and subsequently deposited. Pyroclasts include ash, lapilli, bombs, and blocks, which are classified according to their size and shape.
There are several types of lava, which differ in their viscosity, surface structure, and formation conditions.
Types of Lava and Their Characteristics
Pāhoehoe lava is formed by slow-flowing, hot, and fluid lava with a relatively low viscosity. These properties allow the lava to flow smoothly across the landscape, forming characteristic smooth, glassy, undulating, or rope-like surfaces (knitted or flat lava). The color of this lava varies from dark gray to black.
ʻAʻā lava, on the other hand, forms from a more viscous magma mass that cools more quickly, developing a sharp-edged, lumpy surface. Due to its higher viscosity, this lava moves more slowly than pāhoehoe lava and breaks into rough, irregular blocks. Its color ranges from dark gray to brown.
Pillow lava forms when lava flows underwater and cools extremely quickly upon contact with the cold water. The resulting flows consist of numerous, elongate, interconnecting fingers, each elliptical to circular in cross-section and 0.2-3 m in diameter that may cover the seafloor as an extensive sheet, or grow into a steep-sided heap of overlapping lobes. They are known as pillow lava because when ancient examples have been pushed up out of the sea and exposed in cliffs, they appear to be composed of a pile of discrete pillow-like forms This leads to the formation of characteristic pillow-shaped structures with a glassy crust. Because this type of lava forms under high pressure and low temperatures, the surface of the lava is often riddled with cracks. The color usually ranges from dark gray to black.
Block lava is formed by very viscous lava, which has low fluidity due to its high silicate content. This form of lava often solidifies into large, irregular blocks with sharp edges. The color of block lava varies between dark gray and brown.
Lava bombs are formed by explosive volcanic eruptions, in which fragments of lava are thrown into the air and cooled during flight. As they rotate in the air, these rock fragments often develop aerodynamic shapes such as spindles or chunks. Their color varies from dark gray to reddish, depending on their chemical composition and the degree of oxidation of the iron they contain.
Sources
Wikipedia
Spektrum
mineralienatlas
Own photos