The Cheakamus Valley basalts are a sequence of

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic lava flows along the Cheakamus River in southwestern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. They are part of the

Garibaldi Giuseppe Maria Garibaldi ( , ;In his native Ligurian language, he is known as ''Gioxeppe Gaibado''. In his particular Niçard dialect of Ligurian, he was known as ''Jousé'' or ''Josep''. 4 July 1807 – 2 June 1882) was an Italian general, patr ...

section of the

Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern Calif ...

and were produced during an episode of volcanic eruptions from an unknown vent.Floods, faults, and fire: Geological Field Trips in Washington States and Southwest British Columbia
/ref> The latest basaltic eruption deposited wood in lacustrine sediments under the lava flows that have been dated years old. These youngest lavas form isolated ridges above the older glaciated Cheakamus Valley basalts and were described as "esker-like" by Canadian volcanologist

Bill Mathews William Henry Mathews (1919–2003) was a Canadian geologist, volcanologist, engineer, and professor. He is considered a pioneer in the study of subglacial eruptions and volcano-ice interactions in North America. Many of his publications continu ...

Columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar joint ...

is present all through the most recent basalt lava flow and

pillow basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

s exist in the lowermost unit, portions of which are underlain by

hyaloclastite Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin margin ...

breccia. Bill Mathews suggested that these esker-like lava flows were deposited during

subglacial eruption Subglacial eruptions, those of ice-covered volcanoes, result in the interaction of magma with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcan ...

s that traveled away from the vent inside tunnels or trenches melted in the overlying ice sheet. Mathews based his suggestion on the age of the underlying till, the existence of pillow lava close to the bottom of some lavas that indicate subaqueous volcanism, horizontal jointing at the edges of the lavas that indicate rapid cooling, and the absence of apparent paleotopography to explain these features.

References

Garibaldi Volcanic Belt Pacific Ranges Pleistocene volcanism Lava flows Pleistocene British Columbia {{BritishColumbia-geo-stub

See also

References