Features at convergent plate boundaries with subduction the cross section below shows a subduction zone at an ocean-continent convergent boundary the ocean surface is indicated by a dashed line. 1. drow two arrows on each plate showing which way the plates are moving relative to each other. 2. on the diagram, label features that geologists could use to identify this plate boundary 3. for the features listed below, briefly explain how they formed. volcanoes and mountains: ocean trench: 4. subduction of an ocean plate takes many millions of years. if you were examining a map, what would you look for to indicate that subduction is happening, even if you cannot watch? part 2: sketching a cross section of converging plates with subduction 5. sketch one scenario that might occur when two ocean plates move toward each other. label the trench and volcanoes. ocean plate- ocean plate © w. h. freeman and company lecture tutorials for introductory geoscience 39. history of an ocean below are cross sections of an ocean at different stages of its life cycle, from pre-ocean to post-ocean. the ocean surface is indicated by a dashed line. ocean lithosphere continental lithosphere 1. describe the one plate boundary shown in b. is the ocean growing or shrinking? 2. describe the two plate boundaries shown in e. is the ocean growing or shrinking? 3. arrange the five diagrams in sequential order from pre-ocean to post-ocean. write your order below. youngest oldest 4. two students are debating the order of the stages of an ocean. student 1: i put the cross sections in order from the smallest ocean to the biggest: c-a-d-e-b. i did this because the ocean is growing bigger over time. student 2: but you need to look at the plate boundaries for clues. e has subduction happening, so that means the ocean is shrinking, and that means it was once bigger. with which student do you agree? why? © w. h. freeman and company lecture tutorials for introductory geoscience 40. history of an ocean people often think about the goe of somethina watching changes over time leg. pictures of you as a baby, child, and adult). however, this technique does not work in geology because we cannot watch something change over milions of years. one way to solve this problem os it relates to oceans is to look at the oceans and put them in order of how old they are today (eg, compare a foddler in one city to o teen in another city) 5. match the diagrams from the previous page, which illustrate the stages of an ocean, to the five locations listed below. place the letter next to the stage of ocean formation east african rift atlantic ocean himalayas red sea atlantic ocean ocean pacific ocean - african pacific ocean 6. take your answers to questions 3 and 5 and place the locations on earth in order from the youngest to the oldest in the life cycle of an ocean. youngest oldest 7. two students are debating the locations on earth and their order in the stages of an ocean. student 1: t think the himalayas are the very end of an ocean. they formed as a result of a convergent boundary, so the plates are coming together, which means the ocean that was once there completely shrunk away into nothing. student 2: no. i think the himalayas are the very beginning of an ocean because they are the highest, and then the crust would get thinner and thinner until it becomes an ocean, and the ocean would then grow bigger. with which student do you agree? why? 8. revise the order of your ocean stages in questions 3 and 6 if necessary 9. predict what the red sea will look like in 100 million years. 10. predict what the east coast of the united states could look like in 100 million years. w. h. freeman and company lecture tutorials for introductory geoscience