Geology Bowie Seamount

1 geology

1.1 structure
1.2 eruptive history
1.3 origins

geology
structure

seamounts volcanic mountains rise seafloor. unlimited supply of water surrounding these volcanoes can cause them behave differently volcanoes on land. lava emitted in eruptions @ bowie seamount made of basalt, common gray black or dark brown volcanic rock low in silica content (the lava mafic). when basaltic lava makes contact cold sea water, may cool rapidly form pillow lava, through hot lava breaks form pillow. pillow lava typically fine-grained, due rapid cooling, glassy crust, , has radial jointing.

with height of @ least 3,000 m (10,000 ft) , rising within 24 m (79 ft) of sea surface, bowie seamount shallowest submarine volcano on british columbia coast, in canadian waters, , 1 of shallowest submarine volcanoes in northeast pacific ocean. seamounts found hundreds thousands of metres below sea level, , therefore considered within deep sea. in fact, if bowie seamount on land 600 m (2,000 ft) higher whistler mountain in southwestern british columbia , 800 m (2,600 ft) lower mount robson, highest mountain in canadian portion of rocky mountains.

bowie seamount 55 km (34 mi) long , 24 km (15 mi) wide. flat-topped summit made of weakly consolidated tephra , consists of 2 terraces. lowest terrace 230 m (750 ft) below sea level while highest 80 m (260 ft) below sea level, contains steep-sided secondary summits rise within 25 m (82 ft) below sea level. physical perspective, effective size of submarine volcano considerably large. effects of other submarine volcanoes along pacific northwest, including cobb seamount off coast of washington, can noticed in composition , abundance of tiny floating organisms called plankton 30 km (20 mi) away seamount summit. because of similar size, bowie seamount has similar effect on adjacent waters.

eruptive history

3-d depiction of hodgkins seamount bowie seamount in background

bowie seamount formed submarine eruptions along fissures in seabed throughout last glacial, or wisconsinian , period, began 110,000 years ago , ended between 15,000 , 10,000 years ago. while submarine volcanoes in pacific ocean more 1 million years old, bowie seamount relatively young. base formed less 1 million years ago, summit shows evidence of volcanic activity 18,000 years ago. recent in geological terms, suggesting volcano may yet have ongoing volcanic activity.

close bowie s submerged summit, former coastlines cut wave actions , beach deposits show submarine volcano once have stood above sea level, either single volcanic island or small cluster of shoals have been volcanically active. sea levels during last glacial period, when bowie seamount formed, @ least 100 m (300 ft) lower today.

map of kodiak-bowie seamount chain


origins

there disagreement origin of bowie seamount: geological studies indicate kodiak-bowie seamount chain may have formed above center of upwelling magma called mantle plume. seamounts comprising kodiak-bowie seamount chain formed above mantle plume , carried away mantle plume s magmatic source pacific plate moves in northwesterly direction towards aleutian trench, along southern coastline of alaska.

the volcanic rocks make of seamounts in kodiak-bowie seamount chain unusual in have acid-neutralizing chemical substance typical ocean-island basalts low percentage of strontium found @ mid-ocean ridge basalts. however, strontium-bearing volcanic rocks comprising bowie seamount contain lead. therefore, magma mixtures formed bowie seamount seem have originated varying degrees of partial melting of depleted source in earth s mantle , basalts had distinctly high lead isotopic ratios. estimates during geological studies indicate abundance of depleted-source component ranges 60 80 percent of erupted material.

some aspects of origin of kodiak-bowie seamount chain remain uncertain. volcanic rocks found @ tuzo wilson seamounts south of bowie fresh glassy pillow basalts of recent age, expected if these seamounts located above or close mantle plume south of queen charlotte islands. however, origin of bowie seamount less because though seafloor bowie lies on formed 16 million years ago during late miocene period, bowie s summit shows evidence of recent volcanic activity. if bowie seamount formed above mantle plume @ site presently occupied tuzo wilson seamounts, has been displaced magma source 625 km (390 mi) @ rate of 4 cm (2 in) per year. geologic history of bowie seamount consistent flat-topped eroded summit, source bowie s recent volcanic activity remains uncertain. still others, such dickens seamount , pratt seamount further north of bowie seamount, fall little side of chain s expected trend. hypothesized origin of or seamounts in kodiak-bowie seamount chain formed on top of explorer ridge, divergent tectonic plate boundary west of vancouver island, , have been displaced seafloor spreading.

although of seamounts in kodiak-bowie seamount chain appear follow expected age progression mantle plume trail, others, such denson seamount, older hypothesis suggest. result, kodiak-bowie seamount chain has been proposed geoscientists mix of ridge , mantle plume volcanism.